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Why don't we have two hearts?

Why don't we have two hearts?


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The human body is amazing. But there seems to be some evolutionary changes that appear to not make sense regarding redundancy.

While not necessarily the primary reason for their existence, the human body has a great deal of redundancy.

  • Two eyes.

  • Two arms.

  • Two legs
  • Two ears
  • Two nostrils
  • Two lungs
  • Two kidneys
  • Two sets of teeth
  • A very large liver that can work in part.
  • Two brain hemispheres that can (to some degree) do the work of the other.
  • An appendix that is not critical.

But why do we not have two hearts? It would seem like a good idea to have two smaller hearts, together they work above optimally, but survival would be possible with one.


It is not about redundancy. There are evolutionary and developmental reasons why we have two eyes or two legs and one heart. However just to give you short examples, two eyes are better than one because of our binocular vision while we have two legs because of its locomotor energetics.


Meaning of life

The meaning of life, or the answer to the question: "What is the meaning of life?", pertains to the significance of living or existence in general. Many other related questions include: "Why are we here?", "What is life all about?", or "What is the purpose of existence?" There have been many proposed answers to these questions from many different cultural and ideological backgrounds. The search for life's meaning has produced much philosophical, scientific, theological, and metaphysical speculation throughout history. Different people and cultures believe different things for the answer to this question.

The meaning of life as we perceive it is derived from philosophical and religious contemplation of, and scientific inquiries about existence, social ties, consciousness, and happiness. Many other issues are also involved, such as symbolic meaning, ontology, value, purpose, ethics, good and evil, free will, the existence of one or multiple gods, conceptions of God, the soul, and the afterlife. Scientific contributions focus primarily on describing related empirical facts about the universe, exploring the context and parameters concerning the "how" of life. Science also studies and can provide recommendations for the pursuit of well-being and a related conception of morality. An alternative, humanistic approach poses the question, "What is the meaning of my life?"


Single and Double Circulatory Systems

  • The animal transport system consists of:
    • A fluid medium to transport substances (the Blood)
    • A pump to push the fluid around the body
    • Specialised exchange surfaces

    Most transport systems also contain tubes (Blood Vessels) to hold the blood.

    This is the Circulatory System, which is a very efficient transport system.

    • A Single Circulatory System is a simple loop in which blood flows: Heart > Gills > Body > Heart
    • A Double Circulatory System is a double loop in which blood flows: Heart > Lungs > Heart > Body > Heart

    Fish have a single circulatory system, while mammals have a double circulatory system.

    In a double circulatory system, the loop that goes to the lungs is called the Pulmonary Circuit, while the loop that goes to the body is called the Systemic Circuit.

    The double circulatory system is advantageous for active animals since, while in the single circulatory system the blood pressure is limited by the delicate nature of the tiny capillaries in the gills, in the double circulatory system the blood pressure can be high in the systemic circuit while remaining low and safe in the pulmonary circuit. This allows animals with a double circulatory system to be more active, since blood can reach their respiring tissues faster due to the higher pressure.

    Fish are not as active as other animals, so their single circulatory system is sufficient for their needs, while more active animals like mammals need a double circulatory system.


    What is a Sheep Heart Dissection?

    A sheep heart dissection involves cutting into particular areas of a sheep’s heart so that we can see each of the different sections and learn more about what each part of a heart looks and feels like. A sheep’s heart and sheep internal anatomy are very similar to a human, so it gives us an opportunity to learn more about what a human heart might look like on the inside.

    By dissecting into a heart, we can see each different section in detail and can learn how each section helps in pumping blood around the body. Following is a full explanation and sheep heart dissection guide so that you can easily and safely complete a sheep heart dissection yourself in a lab setting.


    "Athlete's Heart"

    Conditioning causes physical and electrical changes in the heart, creating a beneficial condition called "athlete's heart." Aerobic training, such as running or swimming, causes your heart to develop larger heart chambers. Participants in anaerobic sports, such as weightlifting, increase the thickness and strength of their heart muscles. Mixing the two types of training creates both types of heart improvement. During intense exercise, the hearts of highly trained athletes pump as much as twice the volume of blood as the hearts of untrained people.


    Steps in the Scientific Method

    1 – Make an Observation

    You can’t study what you don’t know is there. This is why scientists are so curious—they’re always looking for patterns, trends, questions, and problems that we don’t understand. Once a scientist finds a really interesting pattern that they want to know more about, they move onto the next step.

    For example, let’s say that you notice a lot of people are drinking alkaline water because they think it’s healthier for them, but you’re not sure if it actually is or not.

    Your turn: What’s something that you find very interesting that you wish you knew more about?

    2 – Ask a Question

    Once a scientist finds an interesting thing to study, they need to ask a question that hopefully they can answer.

    A question that you could ask about alkaline water might be, “Does alkaline water actually make people healthier?”

    Your turn: What is a question you’d like the answer to regarding the interesting thing from step one?

    3 – Do Background Research

    To find out the answer to your question, you need to know what potential answers are. That’s where background research comes in, remembering that not everything you read online is true. Use reliable sources, like Google Scholar…and untamedscience.com!

    In our alkaline water example, you could search online for articles or published scientific papers showing how people change when they drink alkaline water. You could look at overall health, or specific thinks like lung function, blood pH, etc…

    Your turn: Spend a minute or two searching online for some possible answers to your question from step two.

    4 – Form a Hypothesis

    A hypothesis is a statement of what you think the answer to your question is. It’s different from the question you formed because it’s answering the question you developed with a specific prediction that you’ll go on to test. A good hypothesis should be falsifiable, meaning that it’s possible to prove it wrong.

    Let’s say that your background research showed there wasn’t much of an effect on overall health. A hypothesis for this might be: “Drinking alkaline water has no effect on how well people feel.”

    Your turn: What is a potential hypothesis that you might have for your question?

    5 – Conduct an Experiment

    How do you find an answer to your hypothesis? You conduct an experiment to test it! Depending on what a scientist is studying, an experiment can be very quick or take years—some experiments have even been going on for hundreds of years!

    Designing a good experiment is a whole industry that some scientists spend their whole careers working on. But any good science experiment must always serve its one main function: to prove or disprove a hypothesis.

    To develop an experiment for the alkaline water example, you’d need a creative way to get people to drink normal and alkaline water, and ask them to rank how well they feel after drinking each.

    Your turn: What is a good experiment that you could set up to test your hypothesis?

    6 – Analyze Results and Draw a Conclusion

    This is what we’ve all been waiting for—what is the answer to the question? In this step, scientists take a step back, look at the data, and decide whether to accept or reject the hypothesis. Sometimes the conclusion is pretty straightforward, but scientists always do statistical tests just to make sure they’re reading the results correctly.

    Now that you’ve collected your data from the alkaline water experiment, let’s say that there is no real difference in how well people feel based on what type of water they drink. In this case, you’d accept (or, fail to reject) your original hypothesis. Alkaline water would just be a scam that didn’t really affect how well people feel.

    Your turn: What would make you think that your hypothesis is correct or incorrect?

    7 – Report Your Results

    You’ve just tested an important piece of information. It’s something that nobody else in the world knows. What good is that knowledge if you keep it to yourself? The final step of the scientific process is to report your results. Scientists generally report their results in scientific journals, where each report has been checked over and verified by other scientists in a process called peer review.

    If your alkaline water study were real, then you’d need to find a relevant journal and submit your article to them for publication.


    What the Science of Girls Falling in Love Says You Should Do

    Knowing about chemicals and attachment styles alone isn’t going to get a woman to fall in love with you. Knowing how love works, however, can increase the chances of finding the right woman for you and creating a meaningful bond in a way that’s healthy and satisfying for both of you.

    The simple act of touching and cuddling can make the two of you feel closer. Knowing what your chemicals are telling you to do unconsciously can help your conscious, rational mind to accelerate or put on the brakes as needed. Understanding her attachment style can help you give her what she needs in a relationship, or decide to find someone else if your attachment styles don’t match.

    The science of what makes girls fall in love isn’t a magic spell or a Jedi mind trick. It’s the simple act of paying attention to habits, behaviors, and preferences with an eye toward the role science plays in affairs of the heart. You can’t hack into her brain and make her fall in love with you, but you can use your knowledge of how the brain works to nurture and deepen attraction that’s already there. Given enough time and the right compatibility, that attraction can blossom into love — in all its strange, unique, exciting complexity.


    Two kidneys better than one?

    Right now, your kidneys are getting rid of all things your body does not need. They do this by “cleaning” your blood.

    All of this waste will exit your body when you go to the toilet to pee. But your kidneys do a lot more than just clean your blood. They help your bones stay healthy, tell your body when to make new blood cells, and even help you stay upright when you’re walking around all day by taking care of your blood pressure.

    With all those important functions, scientist think having two kidneys must be important for our survival.

    Kidneys ‘clean’ your blood and send waste to your bladder, so you can pee it out. Shutterstock


    How’s your heart rate and why it matters?

    When it comes to your heart rate, it's a bit like the speed of your car. What you want is not too fast, not too slow, and not too erratic. In fact, most of the time, heart rhythm and pace are not things you need to think about. And unless something unusual is going on, you're likely completely unaware of what your heart is doing.

    Heart rate is important because the heart's function is so important. The heart circulates oxygen and nutrient-rich blood throughout the body. When it's not working properly, just about everything is affected. Heart rate is central to this process because the function of the heart (called "cardiac output") is directly related to heart rate and stroke volume (the amount of blood pumped out with each beat).

    Normal heart rate

    A normal heart rate is usually stated as 60 to 100 beats per minute. Slower than 60 is bradycardia ("slow heart") faster than 100 is tachycardia ("fast heart"). But some experts believe that an ideal resting heart rate is closer to 50 to 70. Regardless of what is considered normal, it's important to recognize that a healthy heart rate will vary depending on the situation.

    Here's how to determine your heart rate. First, find your pulse. The side of the neck or front of the wrist are the easiest spots. Then, count the number of beats in 30 seconds. Double this number and that's your heart rate.

    In addition to calculating your heart rate, feeling your pulse can give you an idea of whether the rhythm is regular, irregular, or a mix of both.

    Slow heart rate

    Among healthy people, a slow heart rate may be due to:

    • being physically fit
    • a medication, such as propranolol or metoprolol
    • sleep (though heart rate may rise during the REM stage of sleep).

    On the other hand, a slow heart rate can be a sign of disease, such as:

    • heart attack or other heart disease (such as "sick sinus syndrome")
    • certain infections (including Lyme disease or typhoid fever)
    • high levels of potassium in the blood (hyperkalemia)
    • an underactive thyroid gland.

    Fast heart rate

    Healthy people can have a fast heart rate because they are

    • exercising, especially if it's rigorous or associated with dehydration
    • nervous or excited — while a heart rate over 100 might be considered "abnormal," it is entirely expected if a tiger is headed toward you
    • using a stimulant, such as caffeine or cocaine
    • pregnant.

    Diseases associated with a fast heart rate include:

    • most infections or just about any cause of fever
    • heart problems, for example cardiomyopathy (in which the pumping function of the heart is reduced), atrial fibrillation, or ventricular tachycardia
    • certain medications (such as an EpiPen)
    • low levels of potassium in the blood (hypokalemia)
    • an overactive thyroid gland or too much thyroid medication
    • anemia
    • asthma or other breathing trouble.

    Heart rate and exercise

    Exercise guidelines often suggest moderate to rigorous exercise for 20 to 30 minutes per day, but how do you know if your particular exercise qualifies? You can use your heart rate as a measure of exercise intensity.

    Rigorous exercise will raise your heart rate to 70% to 80% of your maximum heart rate. What's your maximum heart rate? Just subtract your age from 220. So, for a 50-year-old person, 170 is the maximum heart rate. Multiply that number by 0.7 to 0.8 to estimate the 70% to 80% range. For this 50-year-old person, the range would be 119 to 136.

    When should you worry about your heart rate?

    Some people never notice the rate or rhythm of their heart, while others notice every minor irregularity (sometimes called a "skipped beat" or early beat, which happens in all of us). In the absence of symptoms (see below), that's not an indication of trouble. An abnormal rate or rhythm may be discovered during a physical exam, ECG, or other testing, even in healthy people who have no symptoms.

    Common symptoms of a slow heart rate include:

    • fatigue
    • dizziness, lightheadedness, fainting or near-fainting
    • confusion
    • an inability to exercise.

    Common symptoms of a fast heart rate include:

    • fatigue
    • dizziness, lightheadedness, fainting or near-fainting
    • palpitations, or a pounding or fluttering sensation in the chest
    • feeling your heart racing
    • shortness of breath
    • chest pain or tightness.

    As you can see, some of these symptoms overlap, and many can be caused by things other than a heart rate problem. If you have questions or concerns about your heart rate, talk to your doctor. She or he can help you sort this out and recommend testing or follow-up if needed.

    — Robert H. Shmerling, MD

    Image: jovanmandic/Getty Images


    The Heart of the Matter

    Earthworm bodies have an outer layer of muscle, epidermis (skin) and cuticle (protective hard layer). They have between 100 and 150 segments and a tube-like shape, which allows the species to easily move through soil. Its innards, as such, also arrange themselves within this cavity. An earthworm's "hearts" sit near the creature's mouth in five pairs, and function much like a human heart, though earthworms breathe oxygen through their skin and require moisture for respiration. These heart-like organs bear a resemblance to arches, hence the name aortic arch. Some species of annelids regulate heartbeat using their muscles, while earthworms use nerve cells, much like vertebrates. In this way, an earthworm's hearts may seem more similar to a proper, human heart than other members of the annelid grouping. Similarly, annelids have closed circulatory systems, meaning their blood stays within vessels rather than free-flowing in the body, as is the case with some other invertebrates like mollusks.

    After an earthworm "breathes" through its skin, its aortic arches pump the oxygenated blood through its body for use using its dorsal and ventral blood vessels. The dorsal blood vessels carry the blood to the front of the worm, while the ventral blood vessels send it to the worm's backside.