5.2: The States of Matter - Biology

5.2: The States of Matter - Biology

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As described in Section 2.1, a molecule of water is composed of two atoms of hydrogen bonded to one atom of oxygen(H2O). All water molecules are exactly the same (same ratio of elements, same geometric bonding pattern), but we encounter water in three different forms in the world around us. At low temperature, water exists as a solid (ice). As the temperature increases, water exists as a liquid, and at high temperature, as water vapor, a gas. These three forms of water represent the three states of matter: solids, liquids and gases. States of matter are examples of physical properties of a substance. Other physical properties include appearance (shiny, dull, smooth, rough), odor, electrical conductivity, thermal conductivity, hardness and density, to name just a few. We will discuss density in more detail in the next section, but first let’s examine the states of matter and how they differ on an atomic level.

If ice, liquid water and water vapor all consist of identical molecules, then what accounts for the difference in their properties? So far, we have talked about molecules as if they were standing still, but in fact, they are always moving. In chemistry, we often explain the states of matter in terms of the kinetic molecular theory (KMT). The word kinetic refers to motion and the kinetic molecular theory suggests that atoms and molecules are always in motion. The energy associated with this motion is termed kinetic energy. The amount of kinetic energy that a particle has is a direct function of temperature, and it is the kinetic energy of the water molecules under different conditions that determines the different properties of the three states of water.

Atoms and molecules move in different ways under different conditions because of the forces attracting them to each other, called intermolecular forces. Intermolecular forces is a general term describing the fact that all atoms, and molecules share a certain inherent attraction for each other. These attractive forces are much weaker than the bonds that hold molecules together, but in a large cluster of atoms or molecules the sum of all of these attractive forces can be quite significant.

Now, consider a group of molecules or atoms clustered together and held in place by these attractive forces. At low temperature, the molecules or atoms will remain stuck together in a lump of defined shape and structure, like water in the form of an ice cube. This is referred to as the solid phase. At the atomic level, the molecules or atoms in a solid are closely packed, and although they are still all rapidly moving, their movements are so small that they can be thought of as vibrating about a fixed position. As an analogy here, think of a handful of small magnets stuck together in a solid mass. Solids and liquids are the most tightly packed states of matter. Because of the intermolecular forces, solids have a defined shape, which is independent of the container in which they are placed. As energy is added to the system, usually in the form of heat, the individual molecules or atoms acquire enough energy to overcome some of the attractive intermolecular forces between them so that neighboring particles are free to move past or slide over one another. This state of matter is called the liquid phase. As in a solid, in a liquid, the attractive forces are strong enough to hold the molecules or atoms close together so they are not easily compressed and have a definite volume. Unlike in a solid, however, the particles will flow (slide over each other) so that they can assume the shape of their container.

Finally, if enough energy is put into the system, the individual molecules or atoms acquire enough energy to totally break all of the attractive forces between them and they are free to separate and rapidly move throughout the entire volume of their container. This is called the gas phase and atoms or molecules in the gas phase will totally fill whatever container they occupy, taking on the shape and volume of their container. Because there is so much space between the particles in a gas, a gas is highly compressible, which means that the molecules can be forced closer together to fit in a much smaller space. We are all familiar with cylinders of compressed gas, where the compressibility of gasses is exploited to allow a large amount of gas to be transported in a very small space.

Returning to our example of water, at low temperature, water exists as the solid, ice. As the solid is warmed, the water molecules acquire enough energy to overcome the strongest of the attractive forces between them and the ice melts to form liquid water. This transition from the solid phase to the liquid phase happens at a fixed temperature for each substance called the melting point. The melting point of a solid is one of the physical properties of that solid. If we remove energy from the liquid molecules they will slow down enough for the attractive forces to take hold again and a solid will form. The temperature that this happens is called the freezing point and is the same temperature as the melting point.

As more energy is put into the system, the water heats up, the molecules begin moving faster and faster until there is finally enough energy in the system to totally overcome the attractive forces. When this happens, the water molecules are free to fly away from each other, fill whatever container they are occupying and become a gas. The transition from the liquid phase to the gas phase happens at a fixed temperature for each substance and is called the boiling point. Like the melting point, the boiling point is another physical property of a liquid.

Phase transitions for a typical substance can be shown using simple diagram showing the physical states, separated by transitions for melting and boiling points. For example, if you are told that a pure substance is 15˚ C above its boiling point, you can use the diagram to plot the temperature relative to the boiling point. Because you are above the boiling point, the substance will exist in the gas phase.

There are, however, some exceptions to the rules for changes of state that we have just established,. For example, ice is a solid and the molecules in the interior are held together tightly by intermolecular forces. Surface molecules, however, are exposed and they have the opportunity to absorb energy from the environment (think of a patch of snow on a bright sunny day). If some of these surface molecules absorb enough energy, they can break the attractive forces that are holding them and escape as a gas (water vapor) without ever going through the liquid phase. The transition from a solid directly into a gas is called sublimation. The reverse process, a direct transition from a gas to a solid, is called deposition. Perhaps the most common example of a solid that does not melt, but only sublimes, is dry ice (solid carbon dioxide;CO2). This property of dry ice is what makes it a good refrigerant for shipping perishables. It is quite cold, keeping things well frozen, but does not melt into a messy liquid as it warms during shipment.

Just like surface molecules in solids can move directly into the gas phase, surface molecules in liquids also absorb energy from the environment and move into the gas phase, even though the liquid itself is below the boiling point. This is the process of vaporization (evaporation). The reverse process, a transition from a gas to a liquid, is called condensation. Liquid substances undergo vaporization and the space above any liquid has molecules of that substance in the gas state. This is called the vapor pressure of the liquid, and vapor pressure (at a given temperature) is another of the physical properties of liquid substances.

Summarizing what we know about the different states of matter:

In a gas:

  • the molecules or atoms are highly separated, making a gas highly compressible,
  • attractive forces between the particles are minimal, allowing the gas to take on the shape and volume of its container.

In a liquid:

  • the molecules or atoms are closely spaced, making a liquid much less compressible than a gas,
  • attractive forces between the particles are intermediate, allowing the molecules or atoms to move past, or slide over one another,
  • liquids have a definite volume, but will take on the shape of their container.

In a solid:

  • the attractive forces are strong, keeping the atoms or molecules in relatively fixed positions,
  • the neighboring atoms or molecules are close together, making the solid not compressible and giving it a definite shape that is independent of the shape and size of its container.

The most obvious physical properties of a liquid are its retention of volume and its conformation to the shape of its container. When a liquid substance is poured into a vessel, it takes the shape of the vessel, and, as long as the substance stays in the liquid state, it will remain inside the vessel. Furthermore, when a liquid is poured from one vessel to another, it retains its volume (as long as there is no vaporization or change in temperature) but not its shape. These properties serve as convenient criteria for distinguishing the liquid state from the solid and gaseous states. Gases, for example, expand to fill their container so that the volume they occupy is the same as that of the container. Solids retain both their shape and volume when moved from one container to another.

Liquids may be divided into two general categories: pure liquids and liquid mixtures. On Earth, water is the most abundant liquid, although much of the water with which organisms come into contact is not in pure form but is a mixture in which various substances are dissolved. Such mixtures include those fluids essential to life—blood, for example—beverages, and seawater. Seawater is a liquid mixture in which a variety of salts have been dissolved in water. Even though in pure form these salts are solids, in oceans they are part of the liquid phase. Thus, liquid mixtures contain substances that in their pure form may themselves be liquids, solids, or even gases.

The liquid state sometimes is described simply as the state that occurs between the solid and gaseous states, and for simple molecules this distinction is unambiguous. However, clear distinction between the liquid, gaseous, and solid states holds only for those substances whose molecules are composed of a small number of atoms. When the number exceeds about 20, the liquid may often be cooled below the true melting point to form a glass, which has many of the mechanical properties of a solid but lacks crystalline order. If the number of atoms in the molecule exceeds about 100–200, the classification into solid, liquid, and gas ceases to be useful. At low temperatures such substances are usually glasses or amorphous solids, and their rigidity falls with increasing temperature—i.e., they do not have fixed melting points some may, however, form true liquids. With these large molecules, the gaseous state is not attainable, because they decompose chemically before the temperature is high enough for the liquid to evaporate. Synthetic and natural high polymers (e.g., nylon and rubber) behave in this way.

If the molecules are large, rigid, and either roughly planar or linear, as in cholesteryl acetate or p-azoxyanisole, the solid may melt to an anisotropic liquid (i.e., one that is not uniform in all directions) in which the molecules are free to move about but have great difficulty in rotating. Such a state is called a liquid crystal, and the anisotropy produces changes of the refractive index (a measure of the change in direction of light when it passes from one medium into another) with the direction of the incident light and hence leads to unusual optical effects. Liquid crystals have found widespread applications in temperature-sensing devices and in displays for watches and calculators. However, no inorganic compounds and only about 5 percent of the known organic compounds form liquid crystals. The theory of normal liquids is, therefore, predominantly the theory of the behaviour of substances consisting of simple molecules.

A liquid lacks both the strong spatial order of a solid, though it has the high density of solids, and the absence of order of a gas that results from the low density of gases—i.e., gas molecules are relatively free of each other’s influence. The combination of high density and of partial order in liquids has led to difficulties in developing quantitatively acceptable theories of liquids. Understanding of the liquid state, as of all states of matter, came with the kinetic molecular theory, which stated that matter consisted of particles in constant motion and that this motion was the manifestation of thermal energy. The greater the thermal energy of the particle, the faster it moved.


Personality can be defined as a set of characteristics or traits that drive individual differences in human behavior. From a biological perspective, these traits can be traced back to brain structures and neural mechanisms. However, this definition and theory of biological basis is not universally accepted. There are many conflicting theories of personality in the fields of psychology, psychiatry, philosophy, and neuroscience. A few examples of this are the nature vs. nurture debate and how the idea of a 'soul' fits into biological theories of personality. [1]

Since the time of the ancient Greeks, humankind has attempted to explain personality through spiritual beliefs, philosophy, and psychology. Historically, studies of personality have traditionally come from the social sciences and humanities, but in the past two decades neuroscience has begun to be more influential in the understanding of human personality. [2]

However, the most cited and influential figures in publishing the first biology-based personality theories are Hans Eysenck and Jeffrey Alan Gray. Eysenck used both behavioral and psychophysiological methodologies to test and develop his theories. [3] He published a book in 1947 called Dimensions of Personality, describing the personality dimensions of Extraversion and Neuroticism. Gray, a student of Eysenck, studied personality traits as individual differences in sensitivity to rewarding and punishing stimuli. [3] The significance of Gray's work and theories was his use of biology to define behavior, which stimulated a lot of subsequent research. [4]

In 1951, Hans Eysenck and Donald Prell published an experiment in which identical (monozygotic) and fraternal (dizygotic) twins, ages 11 and 12, were tested for neuroticism. It is described in detail in an article published in the Journal of Mental Science. in which Eysenck and Prell concluded that, "The factor of neuroticism is not a statistical artifact, but constitutes a biological unit which is inherited as a whole. neurotic predisposition is to a large extent hereditarily determined." [5] The study concluded that the neuroticism trait was a result of up to eighty percent of genetics. There was a stronger correlation among identical twins rather than fraternal twins. [6]

The idea of biology-based personality research is relatively new, but growing in interest and number of publications. [7] In August 2004, there was a conference specifically on the topic, called The Biological Basis of Personality and Individual Differences. [8] This allowed for presenting and sharing of ideas between psychologists, psychiatrists, molecular geneticists, and neuroscientists, and eventually gave birth to the book under the same title. [8] The book is a collection of current research (as of 2006) in the field contributed by many authors and edited by Turhan Canli. Recently, psychology professor Colin G. DeYoung has even named the idea as the field of "Personality Neuroscience." [9] Furthermore, a journal devoted to cultivating research investigating the neurobiological basis of personality has recently been established and is called "Personality Neuroscience." [10]

There are many theories of personality that centre on the identification of a set of traits that encompass human personality. Few however, are biologically based. This section will describe some theories of personality that have a biological basis.

Eysenck's three-factor model of personality Edit

Eysenck's three-factor model of personality was a causal theory of personality based on activation of reticular formation and limbic system. The reticular formation is a region in the brainstem that is involved in mediating arousal and consciousness. The limbic system is involved in mediating emotion, behavior, motivation, and long-term memory.

    (E) – degree to which people are outgoing and are interactive with people, which is mediated by the activation of the reticular formation. (N) – degree of emotional instability, which is associated with the limbic system. (P) – degree of aggression and interpersonal hostility.

Gray's reinforcement sensitivity theory Edit

Gray's reinforcement sensitivity theory (RST) is based on the idea that there are three brain systems that all differently respond to rewarding and punishing stimuli. [3]

    (FFFS) – mediates the emotion of fear (not anxiety) and active avoidance of dangerous situations. The personality traits associated with this system is fear-proneness and avoidance. (BIS) – mediates the emotion of anxiety and cautious risk-assessment behavior when entering dangerous situations due to conflicting goals. The personality traits associated with this system is worry-proneness and anxiety. (BAS) – mediates the emotion of 'anticipatory pleasure,' resulting from reactions to desirable stimuli. The personality traits associated with this system are optimism, reward-orientation, and impulsivity.

Cloninger model of personality Edit

This model of personality is based on the idea that different responses to punishing, rewarding, and novel stimuli the main characteristics of the human mind is caused by an interaction of the three dimensions below:

    (NS) – degree to which people are impulsive, correlated with low dopamine activity. (HA) – degree to which people are anxious, correlated with high serotonin activity. (RD) – degree to which people are approval seeking, correlated with low norepinephrine activity.

Five factor model of personality Edit

The five factor model (also known as the Big Five) is a widely used personality assessment that describes five core traits that a person possesses:

    – degree to which people enjoy experiencing new stimuli – degree to which people are dutiful and goal-oriented – degree to which people seek stimuli outside of themselves – degree to which people aim to cooperate and please others – degree to which people are emotionally unstable

There is large body of research relating the Big Five traits to individual differences in the brain's structure and function, as measured by MRI-based techniques. A selection of these findings are outlined in the "Brain imaging basis of personality" section below.

Two factor model of personality Edit

A higher-order factor structure can be derived from the Big Five traits, as these traits have often been found to be correlated. Agreeableness, Conscientiousness, and Neuroticism (reversed) can be distilled into a single factor α, or the Stability factor. On the other hand, Extraversion and Openness can be distilled into a single factor β, or the Plasticity factor. [11] [12] These two meta-traits have been shown to be significantly heritable using behavior genetic analysis, [13] which suggests a neurobiological basis that is unique and specific to these meta-traits. Indeed, a growing body of evidence demonstrates that serotonin is associated with Stability and dopamine is associated with Plasticity. [11] [12] [14]

There are many experimental techniques for measuring the biology of the brain, but there are five main methods used to investigate the biological basis of personality. [15] The biological data from these methods are commonly correlated with personality traits. These personality traits are often determined by personality questionnaires. However, personality questionnaires may be biased because they are self-reported. As a result, scientists emphasize using several different measures of personality, [15] [16] rather than solely self-reported measures of personality. For example, another measure of personality traits is observation of behavior. Both humans and animals have been observed to measure personality traits, but animals are particularly useful for studying the long-term behavioral-biological relationship of personality. [17]

Another interesting method that has become more sophisticated and affordable to researchers is the method of whole genome expression analysis. This method involves collecting data for a large number of genes simultaneously which provides many advantages in studying personality. In an article written by Alison M. Bell and Nadia Aubin-Horth, they describe the advantages very clearly by stating, "For one, it is probable that the genetic basis of personality is polygenic, so it makes sense to simultaneously study many genes. In addition, gene products rarely act alone. Instead, they perform their function by interacting together in pathways and networks. As a result, the molecular changes that characterize a phenotype are frequently not based on a single marker or gene, but rather on an entire pathway. Whole genome expression profiling therefore has the potential to reveal new candidates genes and pathways." [18]

Method Function Significance
Electroencephalography (EEG) This method measures electrical activity on the surface of the brain through the scalp, and has the high temporal resolution. [15] Before the advent of brain imaging technology, the only method to measure brain activity was electroencephalography (EEG). [15]
Brain Imaging Brain imaging can refer to either structural or functional imaging. Structural imaging allows for analysis using structural characteristics of the brain, whereas functional imaging involves measuring brain activity. Structural imaging of the brain can be accomplished by using Magnetic Resonance Imaging (MRI). Examples of functional imaging methods include Positron Emission Tomography (PET) and functional MRI (fMRI). PET scans measure the metabolism associated with brain activity, and fMRI measures the flow of blood in the brain, which reflects local brain activity. MRI has particularly high spatial resolution and is entirely non-invasive, whereas PET scans require the injection of radioactive tracers. Brain imaging has catalyzed research of the neurobiological correlates of personality. [3]
Molecular genetics This method is used to analyze a gene-trait link, by measuring the structure and function of genes in the brain. [15] The use of molecular genetics in biology-based personality research is expected to grow. [7]
Molecular assays This method is used to analyze the amount of psychoactive substances, such as hormones and neurotransmitters. Together, these two methods can specifically quantify, define, and manipulate the effects of brain molecules on behavior and personality traits. This has great clinical significance for treatment of personality disorders.
Pharmacological Manipulation This method is used to alter the levels of biochemicals, and observe the effects on behavior.

Neurotransmitters Edit

The biology-based personality theories (discussed below) are based on correlating personality traits with behavioral systems related to motivation, reward, and punishment. On a broad level, this involves the autonomic nervous system, fear-processing circuits in the amygdala, the reward pathway from the ventral tegmental area (VTA) to the nucleus accumbens and prefrontal cortex. All of these circuits heavily rely on neurotransmitters and their precursors, but there has been the most research support for dopamine and serotonin pathways:

    : Dopamine is a monoamine neurotransmitter that has been found to promote exploratory behavior. [19] Dopaminergic pathways have been specifically correlated with the extraversion trait of the Five Factor Model of Personality. [15] The monoamine oxidase (MAO) enzyme has a preferential affinity for dopamine, and its levels are inversely correlated with sensation seeking. [16] : Serotonin is a monoamine neurotransmitter, and has been found to promote avoidance behavior through inhibitory pathways. [19] Specifically, serotonin has been associated with Neuroticism, Agreeableness, and Conscientiousness (traits defined by the Five Factor Model of Personality). [15]

Genes Edit

Previous studies show that genes account for at most 50 percent of a given trait. [1] However, it is widely accepted that variance in gene sequence affect behavior, and genes are a significant risk factor for personality disorders. [20] With the growing interest in using molecular genetics in tracing the biological basis of personality, [8] there may be more gene-trait links found in the future.

Varying polymorphisms and sequence repeats in the gene for dopamine receptor D4 and serotonin transporter gene 5-HTTLPR, have both been found to influence the extraversion trait in adults. Specifically, study participants with at least one copy of the 7-repeat variant of the dopamine receptor D4 gene had higher scores of self-reported extraversion. [8] This suggests that dopamine and serotonin interact to regulate the conflicting behavioral traits of careless exploration vs. cautious inhibition. [19]

Synaptic plasticity Edit

Synaptic plasticity refers to the ability of neurons to strengthen or weaken the connections between them. According to Hebbian theory, these connections are strengthened and maintained through repeated stimulation between neurons. Specifically, there is an emphasis on long-term potentiation (LTP), which is the prolonged strengthening of synaptic connections that facilitate learning from experience.

On a larger scale, there are many pathways and brain regions that are interdependent and contribute to a cohesive, stable personality. For example, the amygdala and hippocampus of the limbic system mediate emotional intensity and consolidate memory of these experiences. But the basic mechanism by which these pathways and brain regions perform these functions, is synaptic plasticity. Ultimately, it boils down to this feature of neurons that allows the brain to learn from repeated experiences, retain memories, and ultimately maintain personality. [21] Joseph LeDoux, an award-winning neuroscientist, asserts that although humans share the same brain systems, it is the unique wiring of neurons that is different in each person and makes their personality. [21]

Over the past two decades, structural magnetic resonance imaging (sMRI) and functional magnetic resonance imaging (fMRI) techniques have been used to study associations between neural activations in the brain and personality traits and other cognitive, social, and emotional processes that characterize personality. Using MRI-based methods for such studies has become increasingly popular due to the non-invasive nature of MRI and the high resolution of MRI.

Structural magnetic resonance imaging Edit

The use of structural magnetic resonance imaging (sMRI) to understand the neurobiological basis of personality and sociocognitive functioning involves assessing the relationship between individual differences in these factors and individual differences in measures of brain structure, such as gray matter volume, cortical thickness, or structural integrity of white matter tracts.

Studies have shown that brain volume is meaningfully correlated with four of the Big Five personality measures. Extraversion was associated with increased volume of medial orbitofrontal cortex, a region associated with processing reward-related stimuli. Conscientiousness was associated with increased volume in the lateral prefrontal cortex, a region involved in planning and the voluntary control of behavior. Agreeableness was associated with increased volume in regions involved in mentalizing, which is the ability to infer the intentions and mental states of other individuals. Neuroticism was associated with increased volume of brain regions associated with threat, punishment, and negative emotions. Openness/Intellect was not significantly correlated with the volume of any brain structures. [22] In another study, neuroticism was negatively correlated with the gray matter volume of the right amygdala, whereas extraversion was positively correlated with gray matter volume of the left amygdala. [23] A separate study also reported a significant association between neuroticism scores and gray matter volume of the left amygdala. [24] In one MRI study, [25] Novelty Seeking correlated with increased grey matter volume in regions of the cingulate cortex, Harm Avoidance correlated with decreased grey matter volume in the orbitofrontal, occipital, and parietal cortex. Reward Dependence correlated with decreased grey matter volume in the caudate nucleus.

A separate but similar line of research has used diffusion tensor imaging to measure the structural integrity of white matter in the brain. One study has shown that neuroticism is negatively correlated with the structural integrity of white matter tracts that connect various brain regions, such as the prefrontal cortex, parietal cortex, amygdala, and other regions in the subcortex. On the other hand, Openness and Agreeableness are positively associated with the structural integrity of these white matter tracts. Openness was also positively associated with the structural integrity of white matter interconnecting dorsolateral prefrontal cortex in both hemispheres. [26]

Functional magnetic resonance imaging Edit

Functional magnetic resonance imaging (fMRI) involves the indirect measurement of neural activity by measuring disturbances in local magnetic fields in the brain. These local disturbances are linked to differential amounts of blood flow to the brain, which is linked to neural activity. Early work using fMRI has studied whether individual differences in personality traits and sociocognitive functioning are associated with individual differences in neural activations in certain brain regions during certain tasks. Such studies have demonstrated associations between single brain regions’ neural responses to certain tasks and individual differences in a wide range of sociocognitive functioning, such as approach/avoidance behavior, [27] sensitivity to rejection, [28] conceptions of the self, [29] [30] and susceptibility to persuasive messages. [31] A small collection of fMRI studies have also demonstrated a significant relationship between brain responses to certain tasks and personality survey measures, such as extraversion and neuroticism. [32] [33]

Over time, neuroscience researchers have recognized that brain regions do not operate in isolation. In fact, the synchronization of firing rates of neurons across different brain regions helps mediate the integration and processing of information across the brain. [34] [35] Thus, studies relating neural activation in single regions to personality measures and associated sociocognitive functioning ignore information about how personality and sociocognitive functioning relate to neural activations across multiple regions in the brain. For example, it is unlikely that neural activation in a single brain region is unilaterally associated with individual differences in personality measures, such as the tendency to down-regulate negative emotions. However, the functional connectivity, or the synchronization of neural activity, between two brain regions can be related to individual differences in personality and sociocognitive functioning. For example, one study found that in an emotion regulation task, coupling of neural responses in the amygdala and the prefrontal cortex was significantly associated with more successful regulation of negative emotions. [36] Other studies shown that neuroticism is associated with relatively low functional connectivity between amygdala and anterior cingulate cortex during a variety of tasks, such as viewing negative emotional stimuli [37] [38] and during a classical conditioning reward task. [39]

Resting-state functional connectivity Edit

Functional connectivity can also be measured at rest, during which individuals are not explicitly engaged in any task. [40] These resting-state functional connectivities can also be related to personality measures and other sociocognitive functioning. For instance, one study found that functional connectivity patterns originating from the amygdala are predictive of neuroticism and extraversion scores. [41] However, personality measures and sociocognitive functioning are not subserved solely by the functional connectivity between two given brain regions. Indeed, examining functional connectivity across the brain may shed more light on the neurobiological basis of personality and sociocognitive functioning. [42] For example, a recent line of research has demonstrated that individual differences in functional connectomes, which are characterized by patterns of spontaneous synchronization of neural activations across the entire brain, are predictive of individual differences in personality and sociocognitive functioning, such as openness to experience, [43] fluid intelligence, [44] and trait levels of paranoia. [45] The use of functional connectomes to predict individual differences is known as “functional connectome fingerprinting” and allows researcher to construct models of personality and sociocognitive functioning based on neural activity across the whole brain rather than within single regions (if using neural activations) or single pairs of regions (if using functional connectivity). [46]


Philosophy in classical Greece is the ultimate origin of the Western conception of the nature of things. [12]

According to Aristotle, the philosophical study of human nature itself originated with Socrates, who turned philosophy from study of the heavens to study of the human things. [16] Though leaving no written works, Socrates is said to have studied the question of how a person should best live. It is clear from the works of his students, Plato and Xenophon, and also from the accounts of Aristotle (Plato's student), that Socrates was a rationalist and believed that the best life and the life most suited to human nature involved reasoning. The Socratic school was the dominant surviving influence in philosophical discussion in the Middle Ages, amongst Islamic, Christian, and Jewish philosophers.

The human soul in the works of Plato and Aristotle has a nature that is divided in a specifically human way. One part is specifically human and rational, being further divided into (1) a part which is rational on its own and (2) a spirited part which can understand reason. Other parts of the soul are home to desires or passions similar to those found in animals. In both Aristotle and Plato, spiritedness (thumos) is distinguished from the other passions (epithūmíā). [17] The proper function of the "rational" was to rule the other parts of the soul, helped by spiritedness. By this account, using one's reason is the best way to live, and philosophers are the highest types of humans.

Aristotle Edit

Aristotle—Plato's most famous student-made some of the most famous and influential statements about human nature. In his works, apart from using a similar scheme of a divided human soul, some clear statements about human nature are made:

  • Man is a conjugal animal: An animal that is born to couple in adulthood. In doing so, man builds a household (oikos) and, in more successful cases, a clan or small village still run upon patriarchal lines. [18]
  • Man is a political animal: An animal with an innate propensity to develop more complex communities (i.e. the size of a city or town), with systems of law-making and a division of labor. This type of community is different in kind from a large family, and requires the special use of human reason. [19]
  • Man is a mimetic animal: Man loves to use his imagination, and not only to make laws and run town councils: "[W]e enjoy looking at accurate likenesses of things which are themselves painful to see, obscene beasts, for instance, and corpses.… [The] reason why we enjoy seeing likenesses is that, as we look, we learn and infer what each is, for instance, 'that is so and so. ' " [20]

For Aristotle, reason is not only what is most special about humanity compared to other animals, but it is also what we were meant to achieve at our best. Much of Aristotle's description of human nature is still influential today. However, the particular teleological idea that humans are "meant" or intended to be something has become much less popular in modern times. [21]

Theory of four causes Edit

For the Socratics, human nature, and all natures, are metaphysical concepts. Aristotle developed the standard presentation of this approach with his theory of four causes, whereby every living thing exhibits four aspects, or "causes:"

For example, an oak tree is made of plant cells (matter) grows from an acorn (effect) exhibits the nature of oak trees (form) and grows into a fully mature oak tree (end). According to Aristotle, human nature is an example of a formal cause. Likewise, our 'end' is to become a fully actualized human being (including fully actualizing the mind). Aristotle suggests that the human intellect ( νοῦς , noûs), while "smallest in bulk", is the most significant part of the human psyche and should be cultivated above all else. [22] The cultivation of learning and intellectual growth of the philosopher is thereby also the happiest and least painful life.

Confucianism Edit

Human nature is a central question in Chinese philosophy. [23] From the Song dynasty, the theory of potential or innate goodness of human beings became dominant in Confucianism. [24]

Mencius Edit

Mencius argues that human nature is good, [23] [25] understanding human nature as the innate tendency to an ideal state that's expected to be formed under the right conditions. [26] Therefore, humans have the capacity to be good, even though they are not all good. [26]

According to Mencian theory, human nature contains four beginnings ( 端 duan ) of morality: [27]

  1. a sense of compassion that develops into benevolence ( 仁 ren )
  2. a sense of shame and disdain that develops into righteousness ( 義 yi )
  3. a sense of respect and courtesy that develops into propriety ( 禮 li ) and
  4. a sense of right and wrong that develops into wisdom ( 智 zhi ). [25][27]

The beginnings of morality are characterized by both affective motivations and intuitive judgments, such as what's right and wrong, deferential, respectful, or disdainful. [27]

In Mencius' view, goodness is the result of the development of innate tendencies toward the virtues of benevolence, righteousness, wisdom, and propriety. [25] The tendencies are manifested in moral emotions for every human being. [25] Reflection ( 思 si ) upon the manifestations of the four beginnings leads to the development of virtues. [25] It brings recognition that virtue takes precedence over satisfaction, but a lack of reflection inhibits moral development. [27] In other words, humans have a constitution comprising emotional predispositions that direct them to goodness. [25]

Mencius also addresses the question why the capacity for evil is not grounded in human nature. [25] If an individual becomes bad, it is not the result of his or her constitution, as their constitution contains the emotional predispositions that direct to goodness, but a matter of injuring or not fully developing his or her constitution in the appropriate direction. [25] He recognizes desires of the senses as natural predispositions distinct from the four beginnings. [27] People can be misled and led astray by their desires if they do not engage their ethical motivations. [25] He therefore places responsibility on people to reflect on the manifestations of the four beginnings. [27] Herein, it is not the function of ears and eyes but the function of the heart to reflect, as sensory organs are associated with sensual desires but the heart is the seat of feeling and thinking. [28] Mencius considers core virtues—benevolence, righteousness, propriety, and wisdom—as internal qualities that humans originally possess, so people can not attain full satisfaction by solely pursuits of self-interest due to their innate morality. [29] Wong (2018) underscores that Mencius' characterization of human nature as good means that "it contains predispositions to feel and act in morally appropriate ways and to make intuitive normative judgments that can with the right nurturing conditions give human beings guidance as to the proper emphasis to be given to the desires of the senses." [27]

Mencius sees ritual (i.e., the standard for how humans should treat and interact with each other) as an outward expression of the inherent moral sense in human nature. [29]

Xunzi Edit

Mencius' view of ritual is in contrast to Xunzi, who does not view moral sense as an innate part of human nature. [30] Rather, a moral sense is acquired through learning, in which one engages in and reflects upon a set of ritual practices. [30] Xunzi's claim that human nature is bad, according to Ivanhoe (1994), means that humans do not have a conception of morality and therefore must acquire it through learning, lest destructive and alienating competition inevitably arises from human desire. [30]

Xunzi understands human nature as the basic faculties, capacities, and desires that people have from birth. [26] He argues that human nature is evil and that any goodness is the result of human activity. [23] [31] It is human nature to seek profit, because humans desire for sensory satisfaction. [31] Xunzi states that "Now the nature of man is evil. It must depend on teachers and laws to become correct and achieve propriety and righteousness and then it becomes disciplined." [23] He underscores that goodness comes from the traits and habits acquired through conscious actions, which he calls artifice ( 偽 wei ). [26] Therefore, morality is seen as a human artifice but not as a part of human nature. [32]

Legalism Edit

Human nature is one of the major pillars of Legalism in China. [33] However, Legalists do not concern themselves with whether human goodness or badness is inborn, and whether human beings possess the fundamental qualities associated with that nature. [33]

Legalists see the overwhelming majority of human beings as selfish in nature. [33] They hold the view that human nature is evil, in which individuals are driven by selfishness. [34] Therefore, people are not expected to always behave morally. [33] For instance, due to the corrupt nature of humans, Legalists did not trust that officials would carry out their duties in a fair and impartial manner. [35] There is a perpetual political struggle, characterized by conflict among contending human actors and interests, where individuals are easily tempted due to their selfish nature at the expense of others. [34]

According to Legalism, selfishness in human nature can not be eliminated or altered by education or self-cultivation. [33] [36] It dismisses the possibility that people can overcome their selfishness and considers the possibility that people can be driven by moral commitment to be exceptionally rare. [33] Legalists do not see the individual morality of both the rulers or the ruled as an important concern in a political system. [33] Instead, Legalist thinkers such as Han Fei emphasize clear and impersonal norms and standards (such as laws, regulations, and rules) as the basis to maintain order. [33]

As human nature has an unchanging selfish but satiable core, Han Fei argues that competition for external goods during times of scarcity produces disorder, while times of abundance simply mean that people do not fall back into chaos and conflict but not that they are necessarily nice. [36] Additionally, Han Fei argues that people are all motivated by their unchanging selfish core to want whatever advantage they can gain from whomever they can gain such advantage, which especially comes to expression in situations where people can act with impunity. [36]

Legalists posit that human selfishness can be an asset rather than a threat to a state. [33] It is axiomatic in Legalism that the government can not be staffed by upright and trustworthy men of service, because every member of the elite—like any member of society—will pursue their own interests and thus must be employed for their interests. [33] Herein, individuals must be allowed to pursue their selfish interests exclusively in a manner that benefits rather than contradicts the needs of a state. [33] Therefore, a political system that presupposes this human selfishness is the only viable system. [33] In contrast, a political system based on trust and respect (rather than impersonal norms and standards) brings great concern with regard to an ongoing and irresolvable power struggle. [33] Rather, checks and controls must be in place to limit the subversion of the system by its actors (such as ministers and other officials). [33] Legalists view the usage of reward and punishment as effective political controls, as it is in human nature to have likes and dislikes. [34] For instance, according to the Legalist statesman Shang Yang, it is crucial to investigate the disposition of people in terms of rewards and penalties when a law is established. [33] He explains that a populace can not be driven to pursuits of agriculture or warfare if people consider these to be bitter or dangerous on the basis of calculations about their possible benefits, but people can be directed toward these pursuits through the application of positive and negative incentives. [33] As an implication of the selfish core in human nature, Han Fei remarks that "Those who act as ministers fear the penalties and hope to profit by the rewards." [36]

In Han Fei's view, the only realistic option is a political system that produces equivalents of junzi (君子, who are virtuous exemplars in Confucianism) but not junzi. [36] This does not mean, however, that Han Fei makes a distinction between seeming and being good, as he does not entertain the idea that humans are good. [36] Rather, as human nature is constituted by self-interest, he argues that humans can be shaped behaviorally to yield social order if it is in the individual's own self-interest to abide by the norms (i.e., different interests are aligned to each other and the social good), which is most efficiently ensured if the norms are publicly and impartially enforced. [36]

In Christian theology, there are two ways of "conceiving human nature:" The first is "spiritual, Biblical, and theistic" and the second is "natural, cosmical, and anti-theistic". [37] : 6 The focus in this section is on the former. As William James put it in his study of human nature from a religious perspective, "religion" has a "department of human nature". [38]

Various views of human nature have been held by theologians. However, there are some "basic assertions" in all "biblical anthropology:" [39]

  1. "Humankind has its origin in God, its creator."
  2. "Humans bear the 'image of God'."
  3. Humans are "to rule the rest of creation".

The Bible contains no single "doctrine of human nature". Rather, it provides material for more philosophical descriptions of human nature. [40] For example, Creation as found in the Book of Genesis provides a theory on human nature. [41]

Catechism of the Catholic Church, under the chapter "Dignity of the human person", provides an article about man as image of God, vocation to beatitude, freedom, human acts, passions, moral conscience, virtues, and sin. [42]

Created human nature Edit

As originally created, the Bible describes "two elements" in human nature: "the body and the breath or spirit of life breathed into it by God". By this was created a "living soul", meaning a "living person". [43] According to Genesis 1:27, this living person was made in the "image of God". [44] From the biblical perspective, "to be human is to bear the image of God." [45] : 18

Genesis does not elaborate the meaning of "the image of God", but scholars find suggestions. One is that being created in the image of God distinguishes human nature from that of the beasts. [46] Another is that as God is "able to make decisions and rule" so humans made in God's image are "able to make decisions and rule". A third is that mankind possesses an inherent ability "to set goals" and move toward them. [45] : 5, 14 That God denoted creation as "good" suggests that Adam was "created in the image of God, in righteousness". [47]

Adam was created with ability to make "right choices", but also with the ability to choose sin, by which he fell from righteousness into a state of "sin and depravity". [45] : 231 Thus, according to the Bible, "humankind is not as God created it." [48]

Fallen human nature Edit

By Adam's fall into sin, "human nature" became "corrupt", although it retains the image of God. Both the Old Testament and the New Testament teach that "sin is universal." [45] : 17, 141 For example, Psalm 51:5 reads: "For behold I was conceived in iniquities and in sins did my mother conceive me." [49] Jesus taught that everyone is a "sinner naturally" because it is mankind's "nature and disposition to sin". [37] : 124–5 Paul, in Romans 7:18, speaks of his "sinful nature". [50]

Such a "recognition that there is something wrong with the moral nature of man is found in all religions." [45] : 141 Augustine of Hippo coined a term for the assessment that all humans are born sinful: original sin. [51] Original sin is "the tendency to sin innate in all human beings". [52] The doctrine of original sin is held by the Catholic Church and most mainstream Protestant denominations, but rejected by the Eastern Orthodox Church, which holds the similar doctrine of ancestral fault.

"The corruption of original sin extends to every aspect of human nature": to "reason and will" as well as to "appetites and impulses". This condition is sometimes called "total depravity". [53] Total depravity does not mean that humanity is as "thoroughly depraved" as it could become. [54] Commenting on Romans 2:14, John Calvin writes that all people have "some notions of justice and rectitude . which are implanted by nature" all people. [55]

Adam embodied the "whole of human nature" so when Adam sinned "all of human nature sinned." [56] The Old Testament does not explicitly link the "corruption of human nature" to Adam's sin. However, the "universality of sin" implies a link to Adam. In the New Testament, Paul concurs with the "universality of sin". He also makes explicit what the Old Testament implied: the link between humanity's "sinful nature" and Adam's sin [57] In Romans 5:19, Paul writes, "through [Adam's] disobedience humanity became sinful." [58] Paul also applied humanity's sinful nature to himself: "there is nothing good in my sinful nature." [59] [60]

The theological "doctrine of original sin" as an inherent element of human nature is not based only on the Bible. It is in part a "generalization from obvious facts" open to empirical observation. [61]

Empirical view Edit

A number of experts on human nature have described the manifestations of original (i.e., the innate tendency to) sin as empirical facts.

  • Biologist Richard Dawkins, in his The Selfish Gene, states that "a predominant quality" in a successful surviving gene is "ruthless selfishness". Furthermore, "this gene selfishness will usually give rise to selfishness in individual behavior." [62]
  • Child psychologist Burton L. White finds a "selfish" trait in children from birth, a trait that expresses itself in actions that are "blatantly selfish". [63][64]
  • Sociologist William Graham Sumner finds it a fact that "everywhere one meets "fraud, corruption, ignorance, selfishness, and all the other vices of human nature". [65] He enumerates "the vices and passions of human nature" as "cupidity, lust, vindictiveness, ambition, and vanity". Sumner finds such human nature to be universal: in all people, in all places, and in all stations in society. [66]
  • Psychiatrist Thomas Anthony Harris, on the basis of his "data at hand", observes "sin, or badness, or evil, or 'human nature', whatever we call the flaw in our species, is apparent in every person." Harris calls this condition "intrinsic badness" or "original sin". [67]

Empirical discussion questioning the genetic exclusivity of such an intrinsic badness proposition is presented by researchers Elliott Sober and David Sloan Wilson. In their book, Unto Others: The Evolution and Psychology of Unselfish Behavior, they propose a theory of multilevel group selection in support of an inherent genetic "altruism" in opposition to the original sin exclusivity for human nature. [68]

20th century Liberal Theology Edit

Liberal theologians in the early 20th century described human nature as "basically good", needing only "proper training and education". But the above examples document the return to a "more realistic view" of human nature "as basically sinful and self-centered". Human nature needs "to be regenerated . to be able to live the unselfish life". [69]

Regenerated human nature Edit

According to the Bible, "Adam's disobedience corrupted human nature" but God mercifully "regenerates". [70] "Regeneration is a radical change" that involves a "renewal of our [human] nature". [71] Thus, to counter original sin, Christianity purposes "a complete transformation of individuals" by Christ. [72]

The goal of Christ's coming is that fallen humanity might be "conformed to or transformed into the image of Christ who is the perfect image of God", as in 2 Corinthians 4:4. [73] The New Testament makes clear the "universal need" for regeneration. [74] A sampling of biblical portrayals of regenerating human nature and the behavioral results follow.

  • being "transformed by the renewing of your minds" (Romans 12:2) [75]
  • being transformed from one's "old self" (or "old man") into a "new self" (or "new man") (Colossians 3:9-10) [76]
  • being transformed from people who "hate others" and "are hard to get along with" and who are "jealous, angry, and selfish" to people who are "loving, happy, peaceful, patient, kind, good, faithful, gentle, and self-controlled" (Galatians 5:20-23) [77]
  • being transformed from looking "to your own interests" to looking "to the interests of others" (Philippians 2:4) [78]

One of the defining changes that occurred at the end of the Middle Ages was the end of the dominance of Aristotelian philosophy, and its replacement by a new approach to the study of nature, including human nature. [ citation needed ] In this approach, all attempts at conjecture about formal and final causes were rejected as useless speculation. [ citation needed ] Also, the term "law of nature" now applied to any regular and predictable pattern in nature, not literally a law made by a divine lawmaker, and, in the same way, "human nature" became not a special metaphysical cause, but simply whatever can be said to be typical tendencies of humans. [ citation needed ]

Although this new realism applied to the study of human life from the beginning—for example, in Machiavelli's works—the definitive argument for the final rejection of Aristotle was associated especially with Francis Bacon. Bacon sometimes wrote as if he accepted the traditional four causes ("It is a correct position that "true knowledge is knowledge by causes." And causes again are not improperly distributed into four kinds: the material, the formal, the efficient, and the final") but he adapted these terms and rejected one of the three:

But of these the final cause rather corrupts than advances the sciences, except such as have to do with human action. The discovery of the formal is despaired of. The efficient and the material (as they are investigated and received, that is, as remote causes, without reference to the latent process leading to the form) are but slight and superficial, and contribute little, if anything, to true and active science. [79]

This line of thinking continued with René Descartes, whose new approach returned philosophy or science to its pre-Socratic focus upon non-human things. Thomas Hobbes, then Giambattista Vico, and David Hume all claimed to be the first to properly use a modern Baconian scientific approach to human things.

Hobbes famously followed Descartes in describing humanity as matter in motion, just like machines. He also very influentially described man's natural state (without science and artifice) as one where life would be "solitary, poor, nasty, brutish and short". [80] Following him, John Locke's philosophy of empiricism also saw human nature as a tabula rasa. In this view, the mind is at birth a "blank slate" without rules, so data are added, and rules for processing them are formed solely by our sensory experiences. [81]

Jean-Jacques Rousseau pushed the approach of Hobbes to an extreme and criticized it at the same time. He was a contemporary and acquaintance of Hume, writing before the French Revolution and long before Darwin and Freud. He shocked Western civilization with his Second Discourse by proposing that humans had once been solitary animals, without reason or language or communities, and had developed these things due to accidents of pre-history. (This proposal was also less famously made by Giambattista Vico.) In other words, Rousseau argued that human nature was not only not fixed, but not even approximately fixed compared to what had been assumed before him. Humans are political, and rational, and have language now, but originally they had none of these things. [82] This in turn implied that living under the management of human reason might not be a happy way to live at all, and perhaps there is no ideal way to live. Rousseau is also unusual in the extent to which he took the approach of Hobbes, asserting that primitive humans were not even naturally social. A civilized human is therefore not only imbalanced and unhappy because of the mismatch between civilized life and human nature, but unlike Hobbes, Rousseau also became well known for the suggestion that primitive humans had been happier, "noble savages". [83]

Rousseau's conception of human nature has been seen as the origin of many intellectual and political developments of the 19th and 20th centuries. [84] He was an important influence upon Kant, Hegel, and Marx, and the development of German idealism, historicism, and romanticism.

What human nature did entail, according to Rousseau and the other modernists of the 17th and 18th centuries, were animal-like passions that led humanity to develop language and reasoning, and more complex communities (or communities of any kind, according to Rousseau).

In contrast to Rousseau, David Hume was a critic of the oversimplifying and systematic approach of Hobbes, Rousseau, and some others whereby, for example, all human nature is assumed to be driven by variations of selfishness. Influenced by Hutcheson and Shaftesbury, he argued against oversimplification. On the one hand, he accepted that, for many political and economic subjects, people could be assumed to be driven by such simple selfishness, and he also wrote of some of the more social aspects of "human nature" as something which could be destroyed, for example if people did not associate in just societies. On the other hand, he rejected what he called the "paradox of the sceptics", saying that no politician could have invented words like " 'honourable' and 'shameful,' 'lovely' and 'odious,' 'noble' and 'despicable ' ", unless there was not some natural "original constitution of the mind". [85]

Hume—like Rousseau—was controversial in his own time for his modernist approach, following the example of Bacon and Hobbes, of avoiding consideration of metaphysical explanations for any type of cause and effect. He was accused of being an atheist. He wrote:

We needn't push our researches so far as to ask "Why do we have humanity, i.e. a fellow-feeling with others?" It's enough that we experience this as a force in human nature. Our examination of causes must stop somewhere. [85]

After Rousseau and Hume, the nature of philosophy and science changed, branching into different disciplines and approaches, and the study of human nature changed accordingly. Rousseau's proposal that human nature is malleable became a major influence upon international revolutionary movements of various kinds, while Hume's approach has been more typical in Anglo-Saxon countries, including the United States. [ citation needed ]

According to Edouard Machery, the concept of human nature is an outgrowth of folk biology and in particular, the concept of folk essentialism - the tendency of ordinary people to ascribe essences to kinds. Machery argues that while the idea that humans have an "essence" is a very old idea, the idea that all humans have a unified human nature is relatively modern for a long time, people thought of humans as "us versus them" and thus did not think of human beings as a unified kind. [86]

The concept of human nature is a source of ongoing debate in contemporary philosophy, specifically within philosophy of biology, a subfield of the philosophy of science. Prominent critics of the concept – David L. Hull, [87] Michael Ghiselin, [88] and David Buller [89] see also [5] [6] [7] – argue that human nature is incompatible with modern evolutionary biology. Conversely, defenders of the concept argue that when defined in certain ways, human nature is both scientifically respectable and meaningful. [5] [6] [7] [90] [91] [92] Therefore, the value and usefulness of the concept depends essentially on how one construes it. This section summarizes the prominent construals of human nature and outlines the key arguments from philosophers on both sides of the debate.

Criticism of the concept of human nature (Hull) Edit

Philosopher of science David L. Hull has influentially argued that there is no such thing as human nature. Hull's criticism is raised against philosophers who conceive human nature as a set of intrinsic phenotypic traits (or characters) that are universal among humans, unique to humans, and definitive of what it is to be a member of the biological species Homo sapiens. In particular, Hull argues that such "essential sameness of human beings" is "temporary, contingent and relatively rare" in biology. [87] He argues that variation, insofar as it is the result of evolution, is an essential feature of all biological species. Moreover, the type of variation which characterizes a certain species in a certain historical moment is "to a large extent accidental" [87] He writes: [87] : 3

Periodically a biological species might be characterized by one or more characters which are both universally distributed among and limited to the organisms belonging to that species, but such states of affairs are temporary, contingent and relatively rare.

Hull reasons that properties universally shared by all members of a certain species are usually also possessed by members of other species, whereas properties exclusively possessed by the members of a certain species are rarely possessed by all members of that species. For these reasons, Hull observes that, in contemporary evolutionary taxonomy, belonging to a particular species does not depend on the possession of any specific intrinsic properties. Rather, it depends on standing in the right kind of relations (relations of genealogy or interbreeding, depending on the precise species concept being used) to other members of the species. Consequently, there can be no intrinsic properties that define what it is to be a member of the species Homo sapiens. Individual organisms, including humans, are part of a species by virtue of their relations with other members of the same species, not shared intrinsic properties.

According to Hull, the moral significance of his argument lies in its impact on the biologically legitimate basis for the concept of "human rights". While it has long been argued that there is a sound basis for "human rights" in the idea that all human beings are essentially the same, should Hull's criticism work, such a basis – at least on a biological level – would disappear. Nevertheless, Hull does not perceive this to be a fundamental for human rights, because people can choose to continue respecting human rights even without sharing the same human nature. [87]

Defences of the concept of human nature Edit

Several contemporary philosophers have attempted to defend the notion of human nature against charges that it is incompatible with modern evolutionary biology by proposing alternative interpretations. They claim that the concept of human nature continues to bear relevance in the fields of neuroscience and biology. Many have proposed non-essentialist notions. Others have argued that, even if Darwinism has shown that any attempt to base species membership on "intrinsic essential properties" is untenable, essences can still be "relational" – this would be consistent with the interbreeding, ecological, and phylogenetic species concepts, which are accepted by modern evolutionary biology. [93] These attempts aim to make Darwinism compatible with a certain conception of human nature which is stable across time.

"Nomological" account (Machery) Edit

Philosopher of science Edouard Machery has proposed that the above criticisms only apply to a specific definition (or "notion") of human nature, and not to "human nature in general". [91] He distinguishes between two different notions:

  • An essentialist notion of human nature - "Human nature is the set of properties that are separately necessary and jointly sufficient for being a human." These properties are also usually considered as distinctive of human beings. They are also intrinsic to humans and inherent to their essence. [91]
  • A nomological notion of human nature - "Human nature is the set of properties that humans tend to possess as a result of the evolution of their species." [91]

Machery clarifies that, to count as being "a result of evolution", a property must have an ultimate explanation in Ernst Mayr's sense. It must be possible to explain the trait as the product of evolutionary processes. Importantly, properties can count as part of human nature in the nomological sense even if they are not universal among humans and not unique to humans. In other words, nomological properties need not be necessary nor sufficient for being human. Instead, it is enough that these properties are shared by most humans, as a result of the evolution of their species – they "need to be typical". [94] Therefore, human nature in the nomological sense does not define what it is to be a member of the species Homo sapiens. Examples of properties that count as parts of human nature on the nomological definition include: being bipedal, having the capacity to speak, having a tendency towards biparental investment in children, having fear reactions to unexpected noises. [91] Finally, since they are the product of evolution, properties belonging to the nomological notion of human nature are not fixed, but they can change over time. [94]

Machery agrees with biologists and others philosophers of biology that the essentialist notion of human nature is incompatible with modern evolutionary biology: we cannot explain membership in the human species by means of a definition or a set of properties. However, he maintains that this does not mean humans have no nature, because we can accept the nomological notion which is not a definitional notion. Therefore, we should think of human nature as the many properties humans have in common as a result of evolution. [91]

Machery argues that notions of human nature can help explain why that, while cultures are very diverse, there are also many constants across cultures. For Machery, most forms of cultural diversity are in fact diversity on a common theme for example, Machery observes that the concept of a kinship system is common across cultures but the exact form it takes and the specifics vary between cultures. [95]

Problems with the nomological account Edit

Machery also highlights potential drawbacks of the nomological account. [91] One is that the nomological notion is a watered-down notion that cannot perform many of the roles that the concept of human nature is expected to perform in science and philosophy. The properties endowed upon humans by the nomological account do not distinguish humans from other animals or define what it is to be human. Machery pre-empts this objection by claiming that the nomological concept of human nature still fulfils many roles. He highlights the importance of a conception which picks out what humans share in common which can be used to make scientific, psychological generalizations about human-beings. [94] One advantage of such a conception is that it gives an idea of the traits displayed by the majority of human beings which can be explained in evolutionary terms.

Another potential drawback is that the nomological account of human nature threatens to lead to the absurd conclusion that all properties of humans are parts of human nature. According to the nomological account, a trait is only part of human nature if it is a result of evolution. However, there is a sense in which all human traits are results of evolution. For example, the belief that water is wet is shared by all humans. However, this belief is only possible because we have, for example, evolved a sense of touch. It is difficult to separate traits which are the result of evolution and those which are not. Machery claims the distinction between proximate and ultimate explanation can do the work here: only some human traits can be given an ultimate explanation, he argues.

According to the philosopher Richard Samuels [92] the account of human nature is expected to fulfill the five following roles:

  • an organizing function that demarks a territory of scientific inquiry
  • a descriptive function that is traditionally understood as specifying properties that are universal across and unique to human being
  • a causal explanatory function that offers causal explanation for occurring human behaviours and features
  • a taxonomic function that specifies possessing human nature as a necessary and sufficient criterion for belonging to the human species
  • Invariances that assume the understanding that human nature is to some degree fixed, invariable or at least hard to change and stable across time.

Samuels objects that Machery's nomological account fails to deliver on the causal explanatory function, because it claims that superficial and co-varying properties are the essence of human nature. Thus, human nature cannot be the underlying cause of these properties and accordingly cannot fulfill its causal explanatory role.

Philosopher Grant Ramsey also rejects Machery's nomological account. For him, defining human nature with respect to only universal traits fails to capture many important human characteristics. [90] Ramsey quotes the anthropologist Clifford Geertz, who claims that "the notion that unless a cultural phenomenon is empirically universal it cannot reflect anything about the nature of man is about as logical as the notion that because sickle-cell anemia is, fortunately, not universal, it cannot tell us anything about human genetic processes. It is not whether phenomena are empirically common that is critical in science. but whether they can be made to reveal the enduring natural processes that underly them." [96] Following Geertz, Ramsey holds that the study of human nature should not rely exclusively on universal or near-universal traits. There are many idiosyncratic and particular traits of scientific interest. Machery's account of human nature cannot give an account to such differences between men and women as the nomological account only picks out the common features within a species. In this light, the female menstrual cycle which is a biologically an essential and useful feature cannot be included in a nomological account of human nature. [90]

Ramsey [90] also objects that Machery uncritically adopts the innate-acquired dichotomy, distinguishing between human properties due to enculturation and those due to evolution. Ramsey objects that human properties do not just fall in one of the two categories, writing that "any organismic property is going to be due to both heritable features of the organism as well as the particular environmental features the organism happens to encounter during its life." [90]

"Causal essentialist" account (Samuels) Edit

Richard Samuels, in an article titled "Science and Human Nature", proposes a causal essentialist view that "human nature should be identified with a suite of mechanisms, processes, and structures that causally explain many of the more superficial properties and regularities reliably associated with humanity." [92] This view is "causal" because the mechanisms causally explain the superficial properties reliably associated with humanity by referencing the underlying causal structures the properties belong to. For example, it is true that the belief that water is wet is shared by all humans yet it is not in itself a significant aspect of human nature. Instead, the psychological process that lead us to assign the word "wetness" to water is a universal trait shared by all human beings. In this respect, the superficial belief that water is wet reveals an important causal psychological process which is widely shared by most human beings. The explanation is also "essentialist" because there is a core set of empirically discoverable cognitive mechanism that count as part of the human nature. According to Samuels, his view avoids the standard biological objections to human nature essentialism.

Samuels argues that the theoretical roles of human nature includes: organizing role, descriptive functions, causal explanatory functions, taxonomic functions, and invariances.

In comparison with traditional essentialist view, the "causal essentialist" view does not accomplish the taxonomic role of human nature (the role of defining what it is to be human). He claims however, that no conception could achieve this, as the fulfillment of the role would not survive evolutionary biologists’ objections (articulated above by in "Criticisms of the concept of human nature"). In comparison with Machery's nomological conception, Samuels wants to restore the causal-explanatory function of human nature. He defines the essence of human nature as causal mechanisms and not as surface-level properties. For instance, on this view, linguistic behaviour is not part of human nature, but the cognitive mechanisms underpinning linguistic behaviour might count as part of human nature.

"Life-history trait cluster" account (Ramsey) Edit

Grant Ramsey proposes an alternative account of human nature, which he names the "life-history trait cluster" account. [90] This view stems from the recognition that the combination of a specific genetic constitution with a specific environment is not sufficient to determine how a life will go, i.e., whether one is rich, poor, dies old, dies young, etc. Many ‘life histories’ are possible for a given individual, each populated by a great number of traits. Ramsey defines his conception of human nature in reference to the “pattern of trait clusters within the totality of extant possible life-histories”. [90] In other words, there are certain life histories, i.e., possible routes one's life can take, for example: being rich, being a PhD student, or getting ill. Ramsey underlines the patterns behind these possible routes by delving into the causes of these life histories. For example, one can make the following claim: “Humans sweat when they get exhausted" or one can also propose neurological claims such as “Humans secrete Adrenaline when they are in flight-fight mode.” This approach enables Ramsey to go beyond the superficial appearances and understand the similarities/differences between individuals in a deeper level which refers to the causal mechanisms (processes, structures and constraints etc.) which lie beneath them. Once we list all the possible life-histories of an individual, we can find these causal patterns and add them together to form the basis of individual nature.

Ramsey's next argumentative manoeuvre is to point out that traits are not randomly scattered across potential life histories there are patterns. “These patterns” he states “provide the basis for the notion of individual and human nature”. [90] : 987 While one's ‘individual nature’ consists of the pattern of trait clusters distributed across that individual's set of possible life histories, Human Nature, Ramsey defines as “the pattern of trait clusters within the totality of extant human possible life histories”. [90] : 987 Thus, if we were to combine all possible life histories of all individuals in existence we would have access to the trait distribution patterns that constitute human nature.

Trait patterns, on Ramsey's account, can be captured in the form of conditional statements, such as "if female, you develop ovaries" or "if male, you develop testes." These statements will not be true of all humans. Ramsey contends that these statements capture part of human nature if they have a good balance of pervasiveness (many people satisfy the antecedent of the conditional statement), and robustness (many people who satisfy the antecedent go on to satisfy the consequent).

Human nature and human enhancement Edit

The contemporary debate between so-called “bioconservatives” and “transhumanists” is directly related to the concept of human nature: transhumanists argue that "current human nature is improvable through the use of applied science and other rational methods." [97] Bioconservatives believe that the costs outweigh the benefits: in particular, they present their position as a defense of human nature which, according to them, is threatened by human enhancement technologies. Although this debate is mainly of an ethical kind, it is deeply rooted in the different interpretations of human nature, human freedom, and human dignity (which, according to bioconservatives, is specific to human beings, while transhumanists think that it can be possessed also by posthumans). As explained by Allen Buchanan, [98] the literature against human enhancement is characterized by two main concerns: that "enhancement may alter or destroy human nature" and that "if enhancement alters or destroys human nature, this will undercut our ability to ascertain the good," as "the good is determined by our nature." [98]

Bioconservatives include Jürgen Habermas, [99] Leon Kass, [100] Francis Fukuyama, [101] and Bill McKibben. [97] Some of the reasons why they oppose (certain forms of) human enhancement technology are to be found in the worry that such technology would be “dehumanizing” (as they would undermine the human dignity intrinsically built in our human nature). For instance, they fear that becoming “posthumans” could pose a threat to “ordinary” humans [102] or be harmful to posthumans themselves. [103] [97]

Jürgen Habermas makes the argument against the specific case of genetic modification of unborn children by their parents, referred to as “eugenic programming” by Habermas. His argument is two-folded: The most immediate threat is on the “ethical freedom” of programmed individuals, and the subsequent threat is on the viability of liberal democracy. Reasoning of the former can be formulated as the following: Genetic programming of desirable traits, capabilities and dispositions puts restrictions on a person's freedom to choose a life of his own, to be the sole author of his existence. A genetically-programmed child may feel alienated from his identity, which is now irreversibly co-written by human agents other than himself. This feeling of alienation, resulted from“contingency of a life's beginning that is not at [one's] disposal,” makes it difficult for genetically-modified persons to perceive themselves as moral agents who can make ethical judgement freely and independently - that is, without any substantial or definitive interference from another agent. Habermas proposes a second threat - the undermining power of genetic programming on the viability of democracy. The basis of liberal democracy, Habermas rightfully claims, is the symmetrical and independent mutual recognition among free, equal and autonomous persons. Genetic programming jeopardizes this condition by irreversibly subjecting children to permanent dependence on their parents, thus depriving them of their perceived ability to be full citizens of the legal community. This fundamental modification to human relationship erodes the foundation of liberal democracy and puts its viability in danger. [104]

The most famous proponent of transhumanism, on the other hand, is Oxford Swedish philosopher Nick Bostrom. According to Bostrom, "human enhancement technologies should be made widely available," [97] as they would offer enormous potential for improving the lives of human beings, without "dehumanizing" them: for instance, improving their intellectual and physical capacities, or protecting them from suffering, illnesses, aging, and physical and cognitive shortcomings. [97] In response to bioconservatives, transhumanists argue that expanding a person's "capability set" would increase her freedom of choice, rather than reducing it. [97]

Allen Buchanan has questioned the relevance of the concept of human nature to this debate. In "Human Nature and Enhancement", he argued that good but also bad characteristics are part of human nature, and that changing the "bad" ones does not necessarily imply that the "good" ones will be affected. Moreover, Buchanan argued that the way we evaluate the good is independent of human nature: in fact, we can "make coherent judgements about the defective aspects of human nature, and if those defects were readied this need not affect our ability to judge what is good". [98] Buchanan's conclusion is that the debate on enhancement of human beings would be more fruitful if it was conducted without appealing to the concept of human nature. [98]

Tim Lewens presented a similar position: since the only notions of human nature which are compatible with biology offer "no ethical guidance in debates over enhancement", we should set the concept of human nature aside when debating about enhancement. On the other hand, "folk", neo-Aristotelian conceptions of human nature seem to have normative implications, but they have no basis in scientific research. [105] Grant Ramsey replied to these claims, arguing that his "life-history trait cluster" account allows the concept of human nature "to inform questions of human enhancement". [106]

Appeals to nature often fall foul of the naturalistic fallacy, whereby certain capacities or traits are considered morally 'good' in virtue of their naturalness. The fallacy was initially introduced by G. E. Moore in 1903, who challenged philosopher's attempts to define good reductively, in terms of natural properties (such as desirable). Reliance on 'the natural' as a justification for resisting enhancement is criticised on several grounds by transhumanists, against the bioconservative motivation to preserve or protect 'human nature'.

For example, Nick Bostrom asserts "had Mother Nature been a real parent, she would have been in jail for child abuse and murder" [107] thus not worthy of unqualified protection. Similarly, Arthur Caplan opposes naturalistic objections to life extension enhancements, by claiming that: [108]

The explanation of why ageing occurs has many of the attributes of a stochastic or chance phenomenon. And this makes ageing unnatural and in no way an intrinsic part of human nature. As such, there is no reason why it is intrinsically wrong to try to reverse or cure ageing.

Instinctual behaviour Edit

Instinctual behaviour, an inherent inclination towards a particular complex behaviour, has been observed in humans. Emotions such as fear are part of human nature (see Fear § Innate fear for example). However they are also known to have been malleable and not fixed (see neuroplasticity and Fear § Inability to experience fear).

Congenital fear of snakes and spiders was found in six-month-old babies. [109] Infant cry is a manifestation of instinct. The infant cannot otherwise protect itself for survival during its long period of maturation. The maternal instinct, manifest particularly in response to the infant cry, has long been respected as one of the most powerful. Its mechanism has been partly elucidated by observations with functional MRI of the mother’s brain. [110]

The herd instinct is found in human children and chimpanzee cubs, but is apparently absent in the young orangutans. [111]

Squeamishness and disgust in humans is an instinct developed during evolution to protect the body and avoid infection by various diseases. [112]

Hormones can affect instinctual behaviour.

Hormones Edit

Testosterone (main male sex hormone) primes several instincts, especially sexuality also dominance, manifest in self-affirmation, the urge to win over rivals (see competitiveness), to dominate a hierarchy (see dominance hierarchy), and to respond to violent signals in men (see aggression), with weakening of empathy. [113] In men, a decrease in testosterone level after the birth of a child in the family was found, so that the father’s energies are more directed to nurturing, protecting and caring for the child. [114] [115] Unduly high levels of this hormone are often associated in a person with aggressiveness, illegal behavior, violence against others, such phenomena as banditry, etc. [ citation needed ] This is confirmed by studies conducted in prisons. [116] [117] The amount of testosterone in men may increase dramatically in response to any competition. [118] In men, the level of testosterone varies depending on whether it is susceptible to the smell of an ovulating or non-ovulatory woman (see menstrual cycle). Men exposed to the odors of ovulating women maintained a stable level of testosterone, which was higher than the level of testosterone in men exposed to non-ovulatory signals. This is due to the fact that an ovulating woman is capable of conceiving, and therefore a man who feels the smell of an ovulating woman is given a signal to sexual activity. [119]

Socioeconomic context Edit

The socioeconomic environment of humans are a context which affect their brain development. [120] It has been argued that H. sapiens is unsustainable by nature – that unsustainability is an inevitable emergent property of his unaltered nature. [121] It has also been argued that human nature is not necessarily resulting in unsustainability but is embedded in and affected by a socioeconomic system that is not having an inevitable structure [122] [ additional citation(s) needed ] – that the contemporary socioeconomic macrosystem affects human activities. [123] A paper published in 1997 concluded that humanity suffer consequences of a "poor fit" between inherited natures and "many of the constructed environments in organizational society". [124] Designing a "cultural narrative" explicitly for living on a finite planet may be suitable for overriding "outdated" innate tendencies. [121]

Human nature – which some have argued to vary to some extent per individual and in time, not be static and, at least in the future, to some extent be purposely alterable [125] – is one of the factors that shape which, how and when human activities are conducted. The contemporary socioeconomic and collective decision-making mechanisms are structures that may affect the expression of human nature – for instance, innate tendencies to seek survival, well-being, respect and status that some consider fundamental to humans [126] may result in varying product-designs, types of work, public infrastructure-designs and the distribution and prevalence of each. As with the nature versus nurture debate, which is concerned whether – or to which degrees – human behavior is determined by the environment or by a person's genes, scientific research is inconclusive about the degree to which human nature is shaped by and manageable by systemic structures as well as about how and to which degrees these structures can and should be purposely altered swiftly globally.

Emergence in Solid State Physics and Biology

There has been much controversy over weak and strong emergence in physics and biology. As pointed out by Phil Anderson in many papers, the existence of broken symmetries is the key to emergence of properties in much of solid state physics. By carefully distinguishing between different types of symmetry breaking and tracing the relation between broken symmetries at micro and macro scales, I demonstrate that the emergence of the properties of semiconductors is a case of strong emergence. This is due to the existence of quasiparticles such as phonons. Furthermore time dependent potentials enable downward causation as in the case of digital computers. Additionally I show that the processes of evolutionary emergence of living systems is also a case of strong emergence, as is the emergence of properties of life out of the underlying physics. A useful result emerges: standard physics theories and the emergent theories arising out of them are all effective theories that are equally valid.

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Investigate Matter Changing States

All stations, but the PLAY and WATCH stations include a reading passage. All reading passages also include audio versions that can be streamed to any device with internet access or loaded on via an MP3.

After students read the passage, they can do a hands-on experiment. In this experiment, students observe how coconut oil changes states as it is heated and cooled.

Here are some photographs of the coconut oil in different states and with the included worksheet filled out.

Also included are differentiated responses. Here is an example of the short answer worksheet.

Learning Standards

Next Generation Science Standards

MS-LS4-2 Apply scientific ideas to construct an explanation for the anatomical similarities and differences among modern organisms and between modern and fossil organisms to infer evolutionary relationships.

Disciplinary Core Ideas – LS4.A: Evidence of Common Ancestry and Diversity
 Anatomical similarities and differences between various organisms living today and between them and organisms in the fossil record, enable the reconstruction of evolutionary history and the inference of lines of evolutionary descent.

NGSS Evidence Statement – Reasoning – Students use reasoning to connect the evidence to support an explanation. Students describe the following chain of reasoning for the explanation… Changes over time in the anatomical features observable in the fossil record can be used to infer lines of evolutionary descent by linking extinct organisms to living organisms through a series of fossilized organisms that share a basic set of anatomical features.

Benchmarks for Science Literacy, American Association for the Advancement of Science

Students should begin to extend their attention from external anatomy to internal structures and functions. Patterns of development may be brought in to further illustrate similarities and differences among organisms. Also, they should move from their invented classification systems to those used in modern biology… A classification system is a framework created by scientists for describing the vast diversity of organisms, indicating the degree of relatedness between organisms, and framing research questions.

Evolution and diversity: Origin of life, evidence of evolution, patterns of evolution, natural selection, speciation, classification and diversity of organisms.

Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.

Life Science (Biology), Grades 6–8.
Classify organisms into the currently recognized kingdoms according to characteristics that they share. Be familiar with organisms from each kingdom.

Biology, High School
5.2 Describe species as reproductively distinct groups of organisms. Recognize that species are further classified into a hierarchical taxonomic system (kingdom, phylum, class, order, family, genus, species) based on morphological, behavioral, and molecular similarities.

Science Projects for Kids: States of Matter

Trying to comprehend the science of matter may seem complicated, but Science Projects for Kids: States of Matter makes understanding it easy and interesting. Explore transitions between solid and liquid by making ice pops and rock candy.

See what happens to soda pop gas in a balloon, and make a cloud in a bottle. Learn about the concept of surface tension by blowing soap bubbles, stretching the surface of water, and cutting and connecting water drops.

You'll be surprised at how much you can learn about states of matter with these simple experiments. Gather a few materials from around the house, round up the kids, and have some science fun.

Follow the links below to get started with science projects for kids that explain the states of matter:

One of the easiest ways to understand how states of matter change is to make yummy ice pops.

Enjoy the sweet rewards of this evaporation test.

Create a very simple water purification system.

Before drinking that soda, see what happens when the gas leaves the bottle.

Create your very own piece of the sky with this project.

Have fun blowing bubbles while learning about surface tension.

See how far you can stretch the surface of water.

Try your luck at splicing and reconnecting water.

Go to the next page to explore changes in states of matter -- and make something good to eat.

For more fun science projects for kids, check out:

Watch the transition from solid to liquid to solid in this science project for kids on states of matter -- and make something good to eat. Solids can change into liquids, and liquids can change into solids. Make ice pops with orange juice, and you can see both transformations.

What You'll Need:

  • Can of frozen orange juice
  • Pitcher
  • Large spoon
  • Water
  • Paper cups
  • Wooden craft sticks

Step 1: Open a can of frozen orange juice, and spoon it into a large pitcher. Touch the frozen juice to feel that it is both solid and cold.

Step 2: Add water according to the package directions to make orange juice.

Step 3: Fill several paper cups about 2/3 of the way with orange juice.

Step 4: Put a craft stick into the liquid in each paper cup.

Step 5: Being careful not to spill, put the cups of juice into the freezer.

Step 6: Check them after two hours. Can you gently pull out the craft stick, or has the liquid orange juice frozen solid around the stick?

Step 7: Once the orange juice has frozen, peel off the paper cups. You and your friends can enjoy a frozen treat!

See the next page to learn how to conduct a science experiment that always has sweet results.

For more fun science projects for kids, check out:

Sugar Crystals on a String

Sugar crystals on a string can be fun to watch grow and delicious to eat. When liquids evaporate into gases, they can leave material behind. That material can be very tasty, as shown by this science project for kids on states of matter. But note that this project requires adult supervision!

What You'll Need:

  • Pan
  • Water
  • Stove
  • Sugar
  • Measuring spoon
  • String
  • Pencil
  • Glass
  • Scissors
  • Button

Step 1: Bring a small pan of water to a boil on the stove, and turn off the heat.

Step 2: Add one tablespoon of sugar, and stir until it dissolves.

Step 3: Continue adding sugar, one tablespoon at a time, letting each tablespoonful dissolve completely before adding the next. When no more sugar will dissolve in the water, allow the saturated solution to cool.

Step 4: Tie a string to the middle of a pencil, and set the pencil across the rim of a glass. Cut the string so that it just touches the bottom of the glass. Tie a button onto the bottom of the string.

Step 5: Pour the cooled sugar water into the glass. Rest the pencil across the rim of the glass so that the string and button are in the solution.

Step 6: Allow the glass to sit in a warm place without being disturbed for several days so that the water evaporates. As the water evaporates, it will leave sugar crystals on the string. You've just made rock candy.

Go to the next page to learn how you can make a simple water purification system.

Joint Statement by the mediators and the observers in the Permanent Conference on Political Issues in the Framework of the Negotiation Process on the Transdniestrian Settlement in the 5+2 format following their 3-4 June 2021 visit to Chisinau and Tiraspol

CHISINAU, 4 June 2021 — The mediators and observers in the Permanent Conference on Political Issues in the Framework of the Negotiation Process on the Transdniestrian Settlement in the 5+2 format visited Chisinau and Tiraspol on 3-4 June 2021 for talks with the Moldovan and Transdniestrian leaderships.

During their visit, the mediators and observers met in Chisinau with Moldovan President, Maia Sandu, Acting Prime Minister, Aureliu Ciocoi, as well as Acting Deputy Prime Minister for Reintegration and Chief Negotiator, Olga Cebotari. In Tiraspol, they met with Transdniestrian leader, Vadim Krasnoselsky, and Chief Negotiator, Vitaly Ignatiev.

The mediators and observers welcomed the dialogue between both Sides on the level of political representatives and joint expert working groups the enhanced co-ordination and interaction of the Sides in addressing the challenges of the COVID-19 pandemic, in particular the distribution of vaccines as well as the recent steps taken towards the restoration of freedom of movement between both banks.

At the same time, they underlined the need for a continued, intensive and constructive dialogue aimed at further strengthening the dynamic in the settlement process. In this respect, they encouraged the Sides to address, as a matter of priority, outstanding technical and practical issues with respect to the joint registration of vehicles from Transdniestria.

The mediators and observers urged the Sides to work towards the full and continuous implementation of the “Berlin-plus” package and encouraged them to develop, based on the progress made in this respect, joint proposals on further confidence-building measures as well as to intensify their dialogue on and efforts with regard to the protection of human rights.

The mediators and observers welcomed in this respect the readiness of both Sides to work towards holding a result-oriented meeting in the 5+2 format in Stockholm this autumn. The mediators and observers further welcomed the readiness of both Sides to address selected priority issues from the joint expert working groups in a retreat in Bavaria, Germany to be organized by the OSCE Mission to Moldova by the end of this year.

Talks in the 5+2 format include representatives of the Sides: Moldova and Transdniestria, the mediators from the OSCE, the Russian Federation and Ukraine, as well as the observers from the European Union and the United States of America.

Exploring the Biological Contributions to Human Health: Does Sex Matter? (2001)

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Exploring the Biological Contributions to Human Health Does Sex Matter? Committee on Understanding the Biology of Sex and Gender Differences Theresa M. Wizemann and Mary-Lou Pardue, Editors Board on Health Sciences Policy INSTITUTE OF MEDICINE NATIONAL ACADEMY PRESS Washington, D.C.

NATIONAL ACADEMY PRESS · 2101 Constitution Avenue, N.W. · Washington, DC 20418 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. Support for this project was provided by the U.S. Department of Health and Human Services (Office on Women's Health, National Institutes of Health Office of Research on Women's Health, National Institute of Environmental Health Sciences, National Institute on Drug Abuse, National Institute of Mental Health, U.S. Food and Drug Administration, Centers for Disease Control and Prevention), the National Science Foundation, the Environ- mental Protection Agency, the National Aeronautics and Space Administration, the Society for Women's Health Research, the Research Foundation for Health and Environmental Effects, Ortho-McNeil/Johnson & Johnson, and the Unilever United States Foundation. The views presented in this report are those of the Committee on Understanding the Biology of Sex and Gender Differences and are not necessarily those of the funding organizations. Library of Congress Cataloging-in-Publication Data Institute of Medicine (U.S.

. Committee on Understanding the Biology of Sex and Gender Differences. Exploring the biological contributions to human health: does sex matter? / Committee on Understanding the Biology of Sex and Gender Differences Theresa M. Wizemann and Mary-Lou Pardue, editors. p. cm. Includes bibliographical references and index. ISBN 0-309-07281-6 (hardcover) 1. Sex differences. 2. Sex factors in disease. [DNLM: 1. Sex Factors. 2. Genetics, Biochemical. 3. Health. 4. Research Design standards. 5. Sex Characteristics. QZ 53 I59e 2001] I. Wizemann, Theresa M. II. Pardue, Mary Lou. III. Title. QP81.5 .156 2001 616'.001� dc21 2001002537 Additional copies of this report are available for sale from the National Academy Press, 2101 Constitution Avenue, N.W., Box 285, Washington, DC 20055. Call (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area), or visit the NAP's home page at The full text of this report is available at For more information about the Institute of Medicine, visit the IOM home page at Copyright 2001 by the National Academy of Sciences. All rights reserved. Printed in the United States of America Cover photograph: Human X and Y Chromosomes (magnified 35,000 times). Source: Biophoto Associates, Photo Researchers, Inc.

"I(nowing is not enough we invest apply. Willing is not enough we invest do." Goethe . . -.-- .-.- . . . .. . . . I NSTITUTE OF MEDICI N E Shaping the Future for Health

National Acaclemy of Sciences National Acaclemy of Engineering Institute of Meclicine National Research Council The National Academy of Sciences is a private, nonprofit, self-perpetuating soci- ety of distinguished scholars engaged in scientific and engineering research, dedi- cated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its mem- bers, sharing with the National Academy of Sciences the responsibility for advis- ing the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sci- ences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal gov- ernment. Functioning in accordance with general policies determined by the Acad- emy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering commu- nities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council.

COMMITTEE ON UNDERSTANDING THE BIOLOGY OF SEX AND GENDER DIFFERENCES MARY-LOU PARDUE (Chair), Boris Magasanik Professor, Department of Biology, Massachusetts Institute of Technology, Cambridge DANIEL L. AZARNOFF, President, D. L. Azarnoff Associates, and Senior Vice President, Clinical/Regulatory Affairs, Cellegy Pharmaceuticals, South San Francisco SHERI BERENBAUM, Professor, Department of Physiology, Southern Illinois University School of Medicine, Carbondale KAREN I. BERKLEY, McKenzie Professor, Program in Neuroscience, Florida State University, Tallahassee ANNE FAUSTO-STERLING, Professor of Biology and Women's Studies, Senior Fellow, Francis Wayland Collegium, Brown University, Providence DANIEL D. FEDERMAN, Senior Dean for Alumni Relations and Clinical Teaching, Carl W. Walter Professor of Medicine and Medical Education, Harvard Medical School, Boston BARBARA ANN GILCHREST, Professor and Chairman, Department of Dermatology, Boston University, Boston MELVIN M. GRUMBACH, Edward B. Shaw Professor of Pediatrics, University of California San Francisco School of Medicine, San Francisco SHIRIKI KUMANYIKA, Associate Dean, Health Promotion and Disease Prevention, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia JUDITH H. LaROSA, Professor, Department of Preventive Medicine and Community Health, State University of New York Downstate Medical Center at Brooklyn, Brooklyn MICHAEL D. LOCKSHIN, Director, Barbara Volcker Center for Women and Rheumatic Disease, Hospital for Special Surgery, and Professor of Medicine, Weill College of Medicine of Cornell University, New York JILL PANETTA, Senior Research Scientist, Research Manager, Lilly Center for Women's Health, Eli Lilly & Company, Indianapolis CARMEN SAPIENZA, Professor of Pathology, Temple University School of Medicine, Philadelphia SALLY E. SHAYWITZ, Professor of Pediatrics, Yale University School of Medicine, New Haven JOHN G. VANDENBERGH, Professor, Department of Zoology, North Carolina State University, Raleigh v

HUNTINGTON F. WILLARD, President and Director, Research Institute of University Hospitals of Cleveland Director, Center for Human Genetics, University Hospitals of Cleveland and Professor, Department of Genetics, Case Western Reserve University, Cleveland Board on Health Sciences Policy Liaison MARY WOOLLEY, President, Research!America, Washington, D.C. IOM Project Staff THERESA M. WIZEMANN, Study Director THELMA COX, Project Assistant SARAH PITLUCK, Research Associate (through rune 2000) IOM Staff ANDREW POPE, Director, Board on Health Sciences Policy ALDEN CHANG, Administrative Assistant DALIA GILBERT, Senior Project Assistant CARLOS GABRIEL, Financial Associate MICHAEL EDINGTON, Managing Editor (through February 2001) Copy Editor MICHAEL K. HAYES Consultant KATHI MANNA Al

Reviewers This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with pro- cedures approved by the National Research Council's (NRC's) Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report: LESLIE Z. BENET, Professor, Department of Biopharmaceutical Sciences, University of California, San Francisco DAVID P. CREWS, Ashbel Smith Professor of Zoology and Psychology, University of Texas at Austin ALICE EAGLY, Professor, Department of Psychology, Northwestern University, Evanston, IL SHERINE E. GABRIEL, Director, Center for Patient Oriented Research, Mayo Clinic, Rochester, MN JANET S. HYDE, Chair, Department of Psychology, University of Wisconsin at Madison ELEANOR E. MACCOBY, Professor Emeritus, Department of Psychology, Stanford University, Stanford v''

V111 REVIEWERS BRUCE S. MCEWEN, Alfred E. Mirsky Professor, Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, New York RUTH B. MERKATZ, Director/Team Leader Pfizer Women's Health, Pfizer Inc., New York, Associate Clinical Professor, Albert Einstein College of Medicine, New York HARRY OSTRER, Associate Professor and Director of Human Genetics Program, Department of Pediatrics, New York University School of Medicine, New York ORA H. PESCOVITZ, Section Director of Pediatrics, Edwin Letzter Professor of Pediatrics, Indiana University, Indianapolis DAVID S. PISETSKY, Professor of Medicine and Professor of Immunology, Duke University Medical Center, Durham, NC CHRISTINE E. SEIDMAN, Professor, Department of Genetics, Harvard Medical School, Boston CAROLINE C. WHITACRE, Professor and Chair, Department of Molecular Virology, Immunology and Medical Genetics, Ohio State University, Columbus Although the reviewers listed above have provided many construc- tive comments and suggestions, they were not asked to endorse the con- clusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by ELIZABETH BARRETT-CONNOR, Professor and Chief, Division of Epidemiology, University of California, San Diego, appointed by the Institute of Medi- cine, and BARBARA CALEEN HANSEN, Professor of Physiology and Director, Obesity and Diabetes Research Center, University of Maryland School of Medicine at Baltimore, appointed by the NRC's Report Review Committee, who were responsible for making certain that an indepen- dent examination of this report was carried out in accordance with insti- tutional procedures and that all review comments were carefully consid- ered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

Preface Does sex matter? Almost anyone would answer "yes" to this simple question. However, subsumed within this question are two much more difficult questions: When does sex matter? and How does sex matter? These two questions define the task undertaken by the Committee on Understanding the Biology of Sex and Gender Differences. This commit- tee was charged with evaluating the current scientific understanding of the answers to these questions with respect to their influence on human health. Specifically, the committee was charged with considering biology at the cellular, developmental, organ, organismal, and behavioral levels. The goal, as in all studies of biology, is to understand the organism in terms of all of the interactions that occur between levels within the organism as well as the mutual interactions between the organism and its environ- ment. This was a broad charge, which required a committee made up of individuals drawn from a wide range of subfields of biology and medi- cine. We have learned much from each other and from a number of in- vited speakers specializing in fields in which the committee did not have expertise. We also made an extensive survey of the relevant literature. The most obvious and best-studied differences between the sexes are in the reproductive systems. Much less work has been done on sex differ- ences in nonreproductive areas of biology, and this is where the commit- tee has focused its efforts. Differences are much less expected in nonre- productive areas of biology, but differences do occur, and some of these differences have important consequences. Understanding these differ- IX

x PREFACE ences makes it possible to design health care more effectively for indi- viduals, both males and females. An additional and more general reason for studying differences be- tween the sexes is that these differences, like other forms of biological variation, can offer important insights into underlying biological mecha- nisms. An often-quoted piece of advice to those studying biology is to "cherish your exceptions." These exceptions traditionally include organ- isms with mutations and organisms from different species that accom- plish the same goal in slightly modified ways. Only relatively recently has it been recognized that sexual variations are as important as these excep- tions in providing similarities and contrasts that can reveal important details about the processes involved. This is an especially opportune time to take stock of what is known about differences and similarities in the basic biology of the sexes, be- cause in the last few years biological research has acquired an arsenal of powerful tools that can be used to answer new questions. Reviews like the one presented in this report juxtapose knowledge from different sub- fields, create new connections between subfields, and inevitably, raise new questions. The arsenal of new tools enables us to answer questions that only a short time ago seemed impossible to answer. The picture that emerges from the study described in this report shows that there are numerous sex differences in nonreproductive tis- sues. Some of these differences can be explained by what we now know. Some are unexplained and point to important questions for future study. Some are large and have known effects on the health of individuals these differences have immediate consequences in terms of health care. Some of the differences are small, with no known effects on health, but they may provide clues that can be used to solve new biological questions. This report provides a broad view of the research and issues that the commit- tee considered. It is, of necessity, a summary with a small number of examples chosen to illustrate the points that we make and to convey the interesting science that is being done in these areas. Sex does matter. It matters in ways that we did not expect. Undoubt- edly, it also matters in ways that we have not begun to imagine. Mary-Lou Pardue, Ph.D. Chair

Acknowledgments The committee is indebted to the experts in many scientific disci- plines who presented informative talks to the committee and participated in lively discussions (see Appendix A). In addition, the committee is grate- ful to the members of the scientific community who made themselves available by phone and e-mail for consultation and technical advice. The committee also wishes to thank the Institute of Medicine staff who contributed to the report. Theresa Wizemann has done a superb job as study director. Thelma Cox has taken very good care of the committee, in spite of severe weather conditions at two of the meetings that pre- sented challenges to her management skills. Sarah Pitluck provided able assistance in the early part of the study and Dalia Gilbert assisted in the later stages. Kathi Hanna, Michael Hayes, and Michael Edington pro- vided helpful style guidance and technical editing. Valerie Setlow helped guide the early development stages of the project. The committee thanks Andrew Pope, Director of the Board on Health Sciences Policy for his continuing interest in this work and guidance throughout the process. Many thanks go to Bruce Alberts, President of the National Academy of Sciences and Chair of the National Research Council, and Ken Shine, President of the Institute of Medicine, for advice and guidance in focusing the task. Thanks also go to the staff of the National Research Council Board on Biology for helpful suggestions and nominations of committee members and reviewers. This report was made possible by the generous support of 14 spon- sors: U.S. Department of Health and Human Services (Office on Women's Health, National Institutes of Health Office of Research on Women's Xl

X11 ACKNOWLEDGMENTS Health, National Institute of Environmental Health Sciences, National Institute on Drug Abuse, National Institute of Mental Health, U.S. Food and Drug Administration, Centers for Disease Control and Prevention), the National Science Foundation, the Environmental Protection Agency, the National Aeronautics and Space Administration, the Society for Women's Health Research, the Research Foundation for Health and Envi- ronmental Effects, Ortho-McNeil/Iohnson & Johnson, and the Unilever United States Foundation. Special thanks go to Phyllis Greenberger of the Society for Women's Health Research, Vivian Pinn of the National Insti- tutes of Health Office of Research on Women's Health, and Susan Wood, formerly of the Office on Women's Health of the U.S. Department of Health and Human Services for their persistence and vision in develop- ing the proposal for this study.

Contents ABSTRACT EXECUTIVE SUMMARY 1 INTRODUCTION Scope of the Report, 14 Sex Differences Beyond the Reproductive System, 19 Evolving Research Policy, 21 Organization of Report, 26 2 EVERY CELL HAS A SEX Sex and the Human Genome, 29 Basic Molecular Genetics: What Is the Potential for Differences Between the Sexes?, 32 Effects of Parental Imprinting on the Expression of Genetic Information, 40 Unexpected or Nonobvious Sex Differences, 41 Genetics as a Tool, 42 Findings and Recommendations, 44 3 SEX BEGINS IN THE WOMB Biology of Sex, 46 Early Development, 50 Puberty, 62 Adulthood, 72 Findings and Recommendations, 77 . . . x''' ax 1 13 28 45

xIv 4 SEX AFFECTS BEHAVIOR AND PERCEPTION Sex Differences in Behavior and Cognitive Abilities, 79 Effects of Hormones on Behavior and Cognition, 89 Sex Differences in Perception of Pain, 105 Animal Models of Cerebrovascular and Cardiovascular Diseases, 112 Findings and Recommendations, 115 5 SEX AFFECTS HEALTH Sex Differences in Response to Therapeutic Agents: Diagnostic and Therapeutic Interventions, 118 Metabolism, Lifestyle, and Physical Performance, 130 Sex Differences in Autoimmune Conditions, 142 A Spectrum of Sex Differences Across a Disease: Coronary Heart Disease, 158 Findings and Recommendations, 170 CONTENTS 79 117 6 THE FUTURE OF RESEARCH ON BIOLOGICAL SEX DIFFERENCES: CHALLENGES AND OPPORTUNITIES 173 Terminology, 174 Research Tools and Resources, 176 Interdisciplinary and Collaborative Research, 181 Non-Health-Related Implications of Research on Sex Differences in Health, 183 REFERENCES APPENDIXES A Data Sources and Acknowledgments B Physiological and Pharmacological Differences Between the Sexes C Glossary D Committee and Staff Biographies INDEX TABLES, FIGURES, AND BOXES Tables 3-1 Some Genes Involved in Human Sex Determination, 53 3-2 Selected Examples of Variations in Sexual Differentiation, 63 185 229 233 239 243 255

CONTENTS 3-3 Life Expectancy at Birth, Age 65, and Age 75 Years, United States, All Races, 1998, 75 xv Sex Prevalence of Some Common Painful Syndromes and Potential Contributing Causes, 106 A Growing List of Therapies for Pain, 110 Sex-Specific Responses to an Experimental Traumatic or Ischemic Cerebral Insult, 113 5-1 Factors Affecting Absorption of Chemicals, 120 5-2 Differences in Drug Concentrations Between the Mother and Fetus and Between Males and Females, 124 5-3 Receptor, Enzyme, and Structural Differences Between Males and Females, 128 5-4 Obesity Prevalence Data for Selected U.S. Adults, by Sex, 135 5-5 Sex Differences in Immunocytes as Determined in Representative Recent Studies, 145 5-6 Sex Differences in Immunization, 146 5-7 Sex Differences in Viral Infections in Humans, 148 5-8 Sex Differences in Mycobacterial, Fungal, and Parasitic Diseases, 149 5-9 Female/Male Ratios Associated with Common Autoimmune Diseases, 150 5-10 Autoimmune Diseases in Which Environmental Triggers Are Prominent, 151 5-11 Peak Ages of Various Autoimmune Diseases, 154 5-12 Animal Models of Human Autoimmune Diseases, 156 5-13 Estimated Risk of Symptoms of Coronary Heart Disease and Death from Myocardial Infarction in Heterozygotes at Different Ages, 160 5-14 Smoking Prevalence by Race and Sex, 1998, 163 5-15 Complications of Acute Myocardial Infarctions, by Sex, 167 5-16 Male: Female Odds Ratios for Use of Diagnostic Procedures for Coronary Heart Disease, 169 Figures 2-1 Schematic representations of two general models used to explain sex differences in gene expressions, 30 Comparison of gene content and gene organization on the X and Y chromosomes, 33 Schematic representation of X-chromosome inactivation in female somatic cells, 36

Xƍt1 Van i CONTENTS 3-1 From genotype to phenotype: a diagrammatic representation of hu- man sex determination and differentiation, 52 Hypothetical diagrammatic representation of the cascade of sex chromosomal and autosomal genes involved in testis determination and the hormones involved in male sex differentiation (representa- tion 1), 56 Hypothetical diagrammatic representation of the cascade of sex chromosomal and autosomal genes involved in testis determination (A) and the hormones involved in male sex differentiation (B) (rep- resentation 2), 57 3-4 Comparison of the pattern of change of serum testosterone (T) levels and hCG and serum pituitary LH (LER-960) and FSH (LER-869) levels in the human male fetus during gestation with morphological changes in the fetal testis, 59 3-5 Adolescent growth spurts in girls and boys (growth velocity curves), 69 3-6 Life expectancy at birth for males and females in several U.S. ethnic groups (data are from 1989 to 1994), 76 Life expectancy at birth for males and females, selected years be- tween 1900 and 1998, United States, all races, 76 Frequency distribution of scores on a hypothetical cognitive test plotted separately by sex, 85 Behavioral development in rodents, 96 Composite images of the distribution of activations upon perfor- mance of rhyme-case tasks (phonological processing) for 19 males and 19 females, 103 5-1 Schematic representation of absorption, distribution, metabolism, and excretion of drugs, 119 5-2 The major affecters of body fat, 132 5-3 Death rates for diseases of the heart by age and sex, 1995-1997, 161 5-4 Age-adjusted high serum cholesterol levels (>240 mg/dl) among individuals ages 20 to 74 years by sex and race, 1988-1994, 163 5-5 Non-age-adjusted high serum cholesterol levels (>240 mg/dl) by sex and age, 164 5-6 5-7 Mortality from coronary heart disease and diabetes in men and women ages 25 to 64, 166 External agents, 171

CONTENTS . . XVII Boxes 1 Summary of Barriers to Progress in Research on Sex Differences, 10 2 Summary of Recommendations, 11 Definitions, 17 Examples of Sex Differences Beyond the Reproductive System, 22 2-1 Genetic Factors That May Differentially Affect the Basic Biochemis- try of Male and Female Cells, 31 Sex Differences in the Relationship of Onset of Pubertal Growth Spurt to Sexual Maturation in Girls and Boys, 67 Sex Differences in the Timing of the Onset of Estrogen Synthesis in Girls and Boys, 68 5-1 Definitions, 118 5-2 Levels and Types of Models for Study of Infection and Inflammation, 143

Abstract One of the most compelling reasons for looking at what is known about the biology of sex differences is that there are striking differences in human disease that are not explained at this time. Being male or female is an important basic human variable that affects health and illness throughout the life span. Differences in health and illness are influenced by individual genetic and physiological constitutions, as well as by an individual's interaction with environmental and experiential factors. The incidence and severity of diseases vary between the sexes and may be related to differences in exposures, routes of entry and the process- ing of aforeign agent, and cellular responses. Although in many cases these sex differences can be traced to the direct or indirect effects of hormones associated with reproduction, differences cannot be solely attributed to hor- mones. Therefore, sex should be considered when designing and analyzing studies in all areas and at all levels of biomedical and health-related re- search. The study of sex differences is evolving into a mature science. There is now sufficient knowledge of the biological basis of sex differences to validate the scientific study of sex differences and to allow the generation of hypoth- eses with regard to health. The next step is to move from the descriptive to the experimental phase and establish the conditions that must be in place to facilitate and encourage the scientific study of the mechanisms and origins of sex differences. Naturally occurring variations in sex differentiation can provide unique opportunities to obtain a better understanding of basic differences and similarities between and within the sexes.

xx ABSTRACT Barriers to the advancement of knowledge about sex differences in health and illness exist and must be eliminated. Scientists conducting research on sex differences are confronted with an array of barriers to progress, includ- ing ethical,financial, sociological, and scientific factors. The committee provides scientific evidence in support of the conclusions presented above and makes recommendations to advance the understand- ing of sex differences and their effects on health and illness.

Florida State Standards for Science: Grade 4

SC.4.N.1.1. Raise questions about the natural world, use appropriate reference materials that support understanding to obtain information (identifying the source), conduct both individual and team investigations through free exploration and systematic investigations, and generate appropriate explanations based on those explorations. 5
Suggested Titles for Florida Science State Standard SC.4.N.1.1.

SC.4.N.1.2. Compare the observations made by different groups using multiple tools and seek reasons to explain the differences across groups. 2
Suggested Titles for Florida Science State Standard SC.4.N.1.2.

SC.4.N.1.3. Explain that science does not always follow a rigidly defined method (''the scientific method'') but that science does involve the use of observations and empirical evidence. 4
Suggested Titles for Florida Science State Standard SC.4.N.1.3.

SC.4.N.1.4. Attempt reasonable answers to scientific questions and cite evidence in support. 4
Suggested Titles for Florida Science State Standard SC.4.N.1.4.

SC.4.N.1.5. Compare the methods and results of investigations done by other classmates. 4
Suggested Titles for Florida Science State Standard SC.4.N.1.5.

SC.4.N.1.6. Keep records that describe observations made, carefully distinguishing actual observations from ideas and inferences about the observations. 2
Suggested Titles for Florida Science State Standard SC.4.N.1.6.

SC.4.N.1.7. Recognize and explain that scientists base their explanations on evidence. 4
Suggested Titles for Florida Science State Standard SC.4.N.1.7.

SC.4.N.1.8. Recognize that science involves creativity in designing experiments. 1
Suggested Titles for Florida Science State Standard SC.4.N.1.8.

SC.4.N.2. The Characteristics of Scientific Knowledge - A: Scientific knowledge is based on empirical evidence, and is appropriate for understanding the natural world, but it provides only a limited understanding of the supernatural, aesthetic, or other ways of knowing, such as art, philosophy, or religion. B: Scientific knowledge is durable and robust, but open to change. C: Because science is based on empirical evidence it strives for objectivity, but as it is a human endeavor the processes, methods, and knowledge of science include subjectivity, as well as creativity and discovery.

SC.4.N.2.1. Explain that science focuses solely on the natural world. 2
Suggested Titles for Florida Science State Standard SC.4.N.2.1.

SC.4.N.3. The Role of Theories, Laws, Hypotheses, and Models - The terms that describe examples of scientific knowledge, for example ''theory,'' ''law,'' ''hypothesis,'' and ''model'' have very specific meanings and functions within science.

SC.4.N.3.1. Explain that models can be three dimensional, two dimensional, an explanation in your mind, or a computer mode. 1
Suggested Titles for Florida Science State Standard SC.4.N.3.1.

FL.SC.4.E. Earth and Space Science

SC.4.E.5. Earth in Space and Time - Humans continue to explore Earth's place in space. Gravity and energy influence the formation of galaxies, including our own Milky Way Galaxy, stars, the Solar System, and Earth. Humankind's need to explore continues to lead to the development of knowledge and understanding of our Solar System.

SC.4.E.5.1. Observe that the patterns of stars in the sky stay the same although they appear to shift across the sky nightly, and different stars can be seen in different seasons. 8
Suggested Titles for Florida Science State Standard SC.4.E.5.1.

SC.4.E.5.2. Describe the changes in the observable shape of the moon over the course of about a month. 6
Suggested Titles for Florida Science State Standard SC.4.E.5.2.

SC.4.E.5.3. Recognize that Earth revolves around the Sun in a year and rotates on its axis in a 24-hour day. 4
Suggested Titles for Florida Science State Standard SC.4.E.5.3.

SC.4.E.5.4. Relate that the rotation of Earth (day and night) and apparent movements of the Sun, Moon, and stars are connected. 1
Suggested Titles for Florida Science State Standard SC.4.E.5.4.

SC.4.E.5.5. Investigate and report the effects of space research and exploration on the economy and culture of Florida. 3
Suggested Titles for Florida Science State Standard SC.4.E.5.5.

SC.4.E.6. Earth Structures - Humans continue to explore the composition and structure of the surface of Earth. External sources of energy have continuously altered the features of Earth by means of both constructive and destructive forces. All life, including human civilization, is dependent on Earth's water and natural resources.

SC.4.E.6.1. Identify the three categories of rocks: igneous, (formed from molten rock) sedimentary (pieces of other rocks and fossilized organisms) and metamorphic (formed from heat and pressure). 5
Suggested Titles for Florida Science State Standard SC.4.E.6.1.

SC.4.E.6.2. Identify the physical properties of common earth-forming minerals, including hardness, color, luster, cleavage, and streak color, and recognize the role of minerals in the formation of rocks. 5
Suggested Titles for Florida Science State Standard SC.4.E.6.2.

SC.4.E.6.3. Recognize that humans need resources found on Earth and that these are either renewable or nonrenewable. 7
Suggested Titles for Florida Science State Standard SC.4.E.6.3.

SC.4.E.6.4. Describe the basic differences between physical weathering (breaking down of rock by wind, water, ice, temperature change, and plants) and erosion (movement of rock by gravity, wind, water, and ice). 3
Suggested Titles for Florida Science State Standard SC.4.E.6.4.

SC.4.E.6.5. Investigate how technology and tools help to extend the ability of humans to observe very small things and very large things. 10
Suggested Titles for Florida Science State Standard SC.4.E.6.5.

SC.4.E.6.6. Identify resources available in Florida (water, phosphate, oil, limestone, silicon, wind, and solar energy). 12
Suggested Titles for Florida Science State Standard SC.4.E.6.6.

FL.SC.4.P. Physical Science

SC.4.P.8. Properties of Matter - A. All objects and substances in the world are made of matter. Matter has two fundamental properties: matter takes up space and matter has mass. B. Objects and substances can be classified by their physical and chemical properties. Mass is the amount of matter (or ''stuff'') in an object. Weight, on the other hand, is the measure of force of attraction (gravitational force) between an object and Earth. The concepts of mass and weight are complicated and potentially confusing to elementary students. Hence, the more familiar term of ''weight'' is recommended for use to stand for both mass and weight in grades K-5. By grades 6-8, students are expected to understand the distinction between mass and weight, and use them appropriately.

SC.4.P.8.1. Measure and compare objects and materials based on their physical properties including: mass, shape, volume, color, hardness, texture, odor, taste, attraction to magnets. 4
Suggested Titles for Florida Science State Standard SC.4.P.8.1.

SC.4.P.8.2. Identify properties and common uses of water in each of its states. 6
Suggested Titles for Florida Science State Standard SC.4.P.8.2.

SC.4.P.8.3. Explore the Law of Conservation of Mass by demonstrating that the mass of a whole object is always the same as the sum of the masses of its parts. 6
Suggested Titles for Florida Science State Standard SC.4.P.8.3.

SC.4.P.8.4. Investigate and describe that magnets can attract magnetic materials and attract and repel other magnets. 3
Suggested Titles for Florida Science State Standard SC.4.P.8.4.

SC.4.P.9. Changes in Matter - A. Matter can undergo a variety of changes. B. Matter can be changed physically or chemically.

SC.4.P.9.1. Identify some familiar changes in materials that result in other materials with different characteristics, such as decaying animal or plant matter, burning, rusting, and cooking. 4
Suggested Titles for Florida Science State Standard SC.4.P.9.1.

SC.4.P.10. Forms of Energy - A. Energy is involved in all physical processes and is a unifying concept in many areas of science. B. Energy exists in many forms and has the ability to do work or cause a change.

SC.4.P.10.1. Observe and describe some basic forms of energy, including light, heat, sound, electrical, and the energy of motion. 17
Suggested Titles for Florida Science State Standard SC.4.P.10.1.

SC.4.P.10.2. Investigate and describe that energy has the ability to cause motion or create change. 9
Suggested Titles for Florida Science State Standard SC.4.P.10.2.

SC.4.P.10.3. Investigate and explain that sound is produced by vibrating objects and that pitch depends on how fast or slow the object vibrates. 4
Suggested Titles for Florida Science State Standard SC.4.P.10.3.

SC.4.P.10.4. Describe how moving water and air are sources of energy and can be used to move things. 3
Suggested Titles for Florida Science State Standard SC.4.P.10.4.

SC.4.P.11. Energy Transfer and Transformations - A. Waves involve a transfer of energy without a transfer of matter. B. Water and sound waves transfer energy through a material. C. Light waves can travel through a vacuum and through matter.

SC.4.P.11.1. Recognize that heat flows from a hot object to a cold object and that heat flow may cause materials to change temperature. SC.4.P.11.2 Identify common materials that conduct heat well or poorly. 3
Suggested Titles for Florida Science State Standard SC.4.P.11.1.

SC.4.P.12. Motion of Objects - A. Motion is a key characteristic of all matter that can be observed, described, and measured. B. The motion of objects can be changed by forces.

SC.4.P.12.1. Recognize that an object in motion always changes its position and may change its direction. 6
Suggested Titles for Florida Science State Standard SC.4.P.12.1.

SC.4.P.12.2. Investigate and describe that the speed of an object is determined by the distance it travels in a unit of time and that objects can move at different speeds. 6
Suggested Titles for Florida Science State Standard SC.4.P.12.2.

FL.SC.4.L. Life Science

SC.4.L.16. Heredity and Reproduction - A. Offspring of plants and animals are similar to, but not exactly like, their parents or each other. B. Life cycles vary among organisms, but reproduction is a major stage in the life cycle of all organisms.

SC.4.L.16.1. Identify processes of sexual reproduction in flowering plants, including pollination, fertilization (seed production), seed dispersal, and germination. 6
Suggested Titles for Florida Science State Standard SC.4.L.16.1.

SC.4.L.16.2. Explain that although characteristics of plants and animals are inherited, some characteristics can be affected by the environment. 3
Suggested Titles for Florida Science State Standard SC.4.L.16.2.

SC.4.L.16.3. Recognize that animal behaviors may be shaped by heredity and learning. 20
Suggested Titles for Florida Science State Standard SC.4.L.16.3.

SC.4.L.16.4. Compare and contrast the major stages in the life cycles of Florida plants and animals, such as those that undergo incomplete and complete metamorphosis, and flowering and nonflowering seed-bearing plants. 16
Suggested Titles for Florida Science State Standard SC.4.L.16.4.

SC.4.L.17. Interdependence - A. Plants and animals, including humans, interact with and depend upon each other and their environment to satisfy their basic needs. B. Both human activities and natural events can have major impacts on the environment. C. Energy flows from the sun through producers to consumers.

SC.4.L.17.1. Compare the seasonal changes in Florida plants and animals to those in other regions of the country. 4
Suggested Titles for Florida Science State Standard SC.4.L.17.1.

SC.4.L.17.2. Explain that animals, including humans, cannot make their own food and that when animals eat plants or other animals, the energy stored in the food source is passed to them. 16
Suggested Titles for Florida Science State Standard SC.4.L.17.2.

SC.4.L.17.3. Trace the flow of energy from the Sun as it is transferred along the food chain through the producers to the consumers.

SC.4.L.17.4. Recognize ways plants and animals, including humans, can impact the environment. 8
Suggested Titles for Florida Science State Standard SC.4.L.17.4.

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