How many different species have existed on Earth?

How many different species have existed on Earth?

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NOTE: Someone else asked this same question a few years back, but it was incorrectly marked as a duplicate and so the question may not have been answered satisfactorily. I'm asking it again, in hopes of getting a stronger answer (if there is one). Please do not mark as a duplicate; I really appreciate it!

(Original question: How many species have existed on earth?, incorrectly marked as a duplicate of: How many organisms have ever lived on Earth?)

QUESTION: How many species have ever existed on Earth, throughout the entirety of Earth's history? For clarity, I'm not asking about the number of individual organisms (answered in 2nd link above), nor about the number of living species estimated to exist today (also cited in an answer in the 2nd link above). All species, ever (never answered in any link, to my knowledge).

From Raup (1986).

Up to 4 billion species of plants and animals are estimated to have lived at some tlme m the geologic past (2), most of these in the last 600 million years (Phanerozoic time). Yet there are only a few million species living today. Thus, extinction of species has been almost as common as origination.

I am not sure how exactly has it been estimated. Read the paper for more details.

In 1991, Raup comments:

Countless species of plants and animals have existed in the history of life on Earth. Estimates of the total progeny of evolution range from 5 to 50 billion species. Yet, only an estimated 5 to 50 million species are alive today - a rather poor survival record. With, at the most, only one in every thousand species surviving, what happened to the others?

Mora et al. (2011) predict ~8.7 million extant eukaryotic species. So I would guess that there are >5 billion (extinct + existing) species on earth.

I guess there will be many more prokaryotes. We don't know anything about ancient prokaryotic species because there are no fossils records. I would say that it would be nearly impossible to estimate the number of prokaryotic species: even now we do not have a very reliable method of typing microbial species (people mostly rely on 16S rRNA sequencing). See What defines a microbial species?

6.24: Biodiversity

  • Contributed by CK-12: Biology Concepts
  • Sourced from CK-12 Foundation

What is biodiversity?

How many species exist? We don't really know for sure. But all those species together, from the smallest bacteria, the deadliest protist, the most bizarre fungi, the prettiest plant, and the biggest mammal, compile the diversity of life, or biodiversity.

A new estimate of biodiversity on Earth

The pie on the left shows a traditional estimate of the relative richness of different groups of organisms based on numbers of described species (Wilson 1992), the middle shows an estimate based on projected richness of different groups (Mora et al. 2011), and the pie on the right shows estimates based on the projected richness of different groups in the present study. Credit: Brendan B. Larsen, Elizabeth C. Miller, Matthew K. Rhodes, and John J. Wiens

Anyone who has studied biology, watched a nature documentary, or, for that matter, simply enjoyed time in the outdoors, has likely been amazed by the variety of plant and animal life on our planet.

To date, about 1.5 million species have been formally described in the scientific literature, most of them insects. Proportionally, bacteria comprise less than 1% of all described species.

Scientists generally agree that many more species exist than are formally described, but they disagree about how many there really are. Some studies have estimated 2 million or fewer, whereas others suggest as many as 12 million (one recent study even suggested the planet could be home to a trillion species).

In a new paper published in The Quarterly Review of Biology (September 2017), researchers from the University of Arizona have estimated that there are roughly 2 billion living species on Earth, over a thousand times more than the current number of described species.

In coming up with their estimate, the researchers took advantage of the fact that many estimates now agree on the projected number of insect species, around 6.8 million. They incorporated new estimates of species boundaries revealed by DNA sequences, which suggest there might be six times as many insect species, increasing the total to 40 million for insect species alone.

They then reviewed all groups of organisms associated with insects as parasites or symbionts. They found that each insect species most likely hosts a unique species of mite, roundworm (nematode), a one-celled fungus called a microsporidian, and a one-celled organism called an apicomplexan protist (which cause malaria in humans).

Most importantly, the researchers estimated that each insect species is likely to host at least 10 bacterial species found nowhere else. Based on these estimates, they deduce that there should be around 2 billion species on Earth.

The authors also suggest that the diagram of which taxonomic groups contain the most species, or the "Pie of Life," is very different from traditional estimates. Rather than being dominated by insects, as traditionally shown, their estimates show a pie dominated by bacteria (70 to 90% of all species), with insects (and animals in general) having a much smaller slice.

Number of species on Earth tagged at 8.7 million

Most precise estimate yet suggests more than 80% of species still undiscovered.

There are 8.7 million eukaryotic species on our planet — give or take 1.3 million. The latest biodiversity estimate, based on a new method of prediction, dramatically narrows the range of 'best guesses', which was previously between 3 million and 100 million. It means that a staggering 86% of land species and 91% of marine species remain undiscovered.

Camilo Mora, a marine ecologist at the University of Hawaii at Manoa, and his colleagues at Dalhousie University in Halifax, Canada, have identified a consistent scaling pattern among the different levels of the taxonomic classification system (order, genus, species and so on) that allows the total number of species to be predicted. The research is published in PLoS Biology 1 today.

Mora argues that knowing how many species there are on Earth is one of the most important questions in science. "Finding this number satisfies a basic scientific curiosity," he says.

Bob May, a zoologist at the University of Oxford, UK, who wrote a commentary on the work 2 , agrees. "Knowing how many plants and animals there are on the planet is absolutely fundamental," he says. He also highlights the practical significance: "Without this knowledge, we cannot even begin to answer questions such as how much diversity we can lose while still maintaining the ecosystem services that humanity depends upon."

But the unstinting efforts of field taxonomists are not going to provide the number any time soon. In the more than 250 years since Swedish biologist Carl Linnaeus began the science of taxonomy, 1.2 million species have been identified and classified — less than 15% of Mora's new total. At this pace, May estimates that it will take another 480 years to complete the job of recording all species.

The catalogue of life

Instead, scientists have tried to predict the total number of species from the number already known. Some of the estimates amount to little more than educated guesses. "These predictions are unverifiable and experts change their mind," says Mora. Other approaches use assumptions that he describes as "unreliable and easy to break".

Mora's method is based on an analysis of the taxonomic classification for all 1.2 million species currently catalogued. Linnaeus's system forms a pyramid-like hierarchy — the lower the category, the more entities it contains. There are more species than genera, more genera than families, more families than orders and so on, right up to the top level, domain.

Mora and his colleagues show that a consistent numerical trend links the numbers in each category, and that this can be used to predict how many entities there should be in poorly catalogued levels, such as species, from the numbers in higher levels that are much more comprehensively described.

However, the method does not work for prokaryotes (bacteria and archaea) because the higher taxonomic levels are not well catalogued as is the case for eukaryotes. A conservative 'lower bound' estimate of about 10,000 prokaryotes is included in Mora's total but, in reality, they are likely to number in the millions.

"The unique thing about this approach is that we are able to validate it," he says. "By testing the predictions against well catalogued groups such as mammals, birds, reptiles and amphibians, we were able to show that we could predict the correct number of species."

The analysis also reveals that some groups are much better known than others. For example, some 72% of the predicted 298,000 plant species on land have already been documented, in comparison with only 12% of predicted land animal species and 7% of predicted land fungi species.

May is impressed. "I like this approach. Not only is it imaginative and novel, but the number it comes up with is within the range of my own best estimate!"

Explorations Through Time - Life Has a History

1. How many different species of living things exist today? ___________________
2. Which group of animals has the largest number of species? _______________________
3. How many mammal species exist today? ______________

4. Number the organisms from 1 (most abundant) to 8 (least abundant)
____ Mammals ____ Molluscs___ Roundworms ____ Arthropods ____ Flatworms

5. What is biodiversity (click on the purple links for definitions): _______________________________

6. 470 Million Years Ago (click circle for a "closer look" at the period)
What was the name of the period? ________________________
What was the dominant predator? ____________________________
What was the first arthropod? ________________________

7. 160 Million Years Ago
What was the name of the period? _____________________________
What large marine reptile existed? _____________________________

8. How old is the earth? _______________________
9. Fill in the blanks of the timeline

10. The best source of evidence for determining events in earth's history is ______________
11. What is a paleontologist? __________________________

12. Identify three fossils from the image. Name them and point to them with an arrow

13. What features are found in therapods? _____________________________________
14. What is a cladogram? ________________________________________
15. What is divergence? _____________________________________

16. To which animal are the crane and eagle most closely related? _______________________
17. What other data (besides physical features) do scientists use to find if organisms are related? List 3 things. _______________________________________
18. What birds on the Galapagos islands were adapted to different regions? ________________
19. The beaks of the birds vary with what? ___________________________________
20. What would happen if the environment changed and only plants with larger, harder seeds survived.How do you think that might affect the population of Geospiza fortis finches? _____________________________________
21. What is geographic isolation? _____________________________________________
22. Identify the extinct creature. _________________________________________
23. Name two animals that have gone extinct since humans have been present? ________________________

/>This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.

Did another advanced species exist on Earth before humans?

Our Milky Way galaxy contains tens of billions of potentially habitable planets, but we have no idea whether we’re alone. For now Earth is the only world known to harbor life, and among all the living things on our planet we assume Homo sapiens is the only species ever to have developed advanced technology.

But maybe that’s assuming too much.

In a mind-bending new paper entitled “The Silurian Hypothesis” — a reference to an ancient race of brainy reptiles featured in the British science fiction show "Doctor Who" — scientists at NASA’s Goddard Institute for Space Studies and the University of Rochester take a critical look at the scientific evidence that ours is the only advanced civilization ever to have existed on our planet.

“Do we really know we were the first technological species on Earth?” asks Adam Frank, a professor of physics and astronomy at Rochester and a co-author of the paper. “We’ve had an industrial society for only about 300 years, but there’s been complex life on land for nearly 400 million years.”

If humans went extinct today, Frank says, any future civilization that might arise on Earth millions of years hence might find it hard to recognize traces of human civilization. By the same token, if some earlier civilization existed on Earth millions of years ago, we might have trouble finding evidence of it.

In search of lizard people

The discovery of physical artifacts would certainly be the most dramatic evidence of a Silurian-style civilization on Earth, but Frank doubts we’ll ever find anything of the sort.

“Our cities cover less than one percent of the surface,” he says. Any comparable cities from an earlier civilization would be easy for modern-day paleontologists to miss. And no one should count on finding a Jurassic iPhone it wouldn't last millions of years, Gorilla Glass or no.

Finding fossilized bones is a slightly better bet, but if another advanced species walked the Earth millions of years ago — if they walked — it would be easy to overlook their fossilized skeletons — if they had skeletons. Modern humans have been around for just 100,000 years, a thin sliver of time within the vast and spotty fossil record.

For these reasons, Frank and Gavin Schmidt, a climatologist at Goddard and the paper's co-author, focus on the possibility of finding chemical relics of an ancient terrestrial civilization.

Using human technology as their guide, Schmidt and Frank suggest zeroing in on plastics and other long-lived synthetic molecules as well as radioactive fallout (in case factions of ancient lizard people waged atomic warfare). In our case, technological development has been accompanied by widespread extinctions and rapid environmental changes, so those are red flags as well.

After reviewing several suspiciously abrupt geologic events of the past 380 million years, the researchers conclude that none of them clearly fit a technological profile. Frank calls for more research, such as studying how modern industrial chemicals persist in ocean sediments and then seeing if we can find traces of similar chemicals in the geologic record.

He argues that a deeper understanding of the human environmental footprint will also have practical consequences, helping us recognize better ways to achieve a long-term balance with the planet so we don't end up as tomorrow's forgotten species.

Then again, he’s also a curious guy who's interested in exploring more far-out ideas for finding Silurian-style signatures: “You could try looking on the moon,” he says.

Lunar archaeology

The moon is a favored target of Penn State University astronomer Jason Wright, one of a handful of other researchers now applying serious scientific thinking to the possibility of pre-human technological civilizations.

“Habitable planets like Earth are pretty good at destroying unmaintained things on their surfaces,” Wright says. So he’s been looking at the exotic possibility that such a civilization might have been a spacefaring one. If so, artifacts of their technology, or technosignatures, might be found elsewhere in the solar system.


Mach Space aliens could have died out long ago, scientist says

Wright suggests looking for such artifacts not just on the lunar surface, but also on asteroids or buried on Mars — places where such objects could theoretically survive for hundreds of millions or even billions of years.

SpaceX’s recent launch of a Tesla Roadster into space offers an insight into how such a search might go. Several astronomers pointed their telescopes at the car and showed that, even if you had no idea what you were looking at, you’d still quickly pick it out as one weird-looking asteroid.

Finding technosignatures in space is an extreme long shot, but Wright argues that the effort is worthwhile. “There are lots of other reasons to find peculiar structures on Mars and the moon, and to look for weird asteroids,” he says. Such studies might reveal new details about the history and evolution of the solar system, for instance, or about resources that might be useful to future spacefarers.

If the efforts turn up a big black obelisk somewhere, so much the better.

Three human-like species lived side-by-side in ancient Africa

The findings underline a growing understanding that the present-day situation, where one human species dominates the globe, may be unusual compared with the evolutionary past.

The new evidence comes from efforts to date bones uncovered at a cave complex near Johannesburg.

The new work also revealed the earliest known example of Homo erectus, a species thought to be a direct ancestor of modern humans (Homo sapiens).

The three groups of hominins (human-like creatures) belonged to Australopithecus (the group made famous by the "Lucy" fossil from Ethiopia), Paranthropus and Homo - better known as humans.

Andy Herries, from LaTrobe University in Melbourne, Australia, and colleagues evaluated remains found at the Drimolen Cave Complex using three different scientific dating techniques: electron spin resonance, palaeomagnetism and uranium-lead dating.

"We collated all of the dates from each of these techniques and together they showed that we had a very precise age. We now know that the Drimolen Main Quarry and all of the fossils in it are dated from 2.04 to 1.95 million years ago," said co-author Stephanie Baker, from the University of Johannesburg.

The Drimolen complex has produced multiple ancient fossils over the years, including those of ancient hominins.

But a few years ago, researchers uncovered two new skullcaps. One of these belonged to the relatively primitive species Paranthropus robustus. The other was more modern in appearance and was identified as Homo erectus. They named the H. erectus skullcap DNH 134.

Homo erectus is one of our direct human ancestors and may have been the first early human species to migrate out of Africa into the rest of the world. Not only is this the earliest example of the species anywhere in the world, but it's the only specimen known from South Africa.

"Until this find, we always assumed Homo erectus originated from eastern Africa. But DNH 134 shows that Homo erectus, one of our direct ancestors, possibly comes from southern Africa instead," said Stephanie Baker.

"That would mean that they later moved northwards into East Africa. From there they went through North Africa to populate the rest of the world."

We once thought of human evolution as a linear progression, with modern humans emerging at the end as the pinnacle of evolutionary development. But everywhere we look, it's increasingly clear the real picture was much messier.

As a case in point, another study published this week in Nature journal used modern techniques to date a well-preserved skull found in a quarry at Kabwe, Zambia, in 1921. The skull which is more primitive than those of modern humans, but more advanced than Homo erectus, was considered to be around 500,000 years old based on its anatomy.

It is considered by many researchers to belong to a species called Homo heidelbergensis - a common ancestor of modern humans and Neanderthals.

But scientists who have dated small samples of bone and teeth from the skull,as well as other material associated with the specimen, have shown that it is much younger - between 324,000 and 276,000 years old.

Lead author Prof Chris Stringer, from the Natural History Museum in London, UK, said: "This is surprisingly young, as a fossil at about 300,000 years old would be expected to show intermediate features between H. heidelbergensis and H. sapiens. But Broken Hill shows no significant features of our species."

The discovery implies that at least three different Homo species co-existed at this time in Africa.

Prof Stringer added: "Previously, the Broken Hill skull was viewed as part of a gradual and widespread evolutionary sequence in Africa from archaic humans to modern humans. But now it looks as if the primitive species Homo naledi survived in southern Africa, H. heidelbergensis was in south-central Africa, and early forms of our species existed in regions like Morocco and Ethiopia."

In yet another important human evolution study this week, researchers analysed ancient proteins from 1.9-million-year-old Homo erectus fossils found at Dmanisi in Georgia and from a species known as Homo antecessor, which is thought to have been present in Spain from 1.2 million years ago to 800,000 years ago.

The protein analysis helped establish relationships between the two species and other hominins for which we have DNA data. The use of proteins is helping extend our knowledge of evolutionary relationships beyond the ages at which it becomes difficult to obtain DNA evidence, because of the breakdown of the molecule over time.

The study showed that H. antecessor, whose validity as a separate species has been questioned in the past, is a close sister lineage to modern humans and other recent Homo species, such as Neanderthals and Denisovans.

Question: why are there so many different species of animals on earth?

The emotional and human answer is – why not? Isn’t it great?

But let’s be scientific. A species exists if it can. If the conditions are right – there is food, it’s the right temperature, it can produce babies and so on. The set of conditions that’s right for a species is called a “niche”. As the conditions change (e.g. as the world becomes warmer or colder) so will the species change. Elephants might grow hair and evolve into mammoths if we hit an ice age. The idea is that nothing is ever constant. Evolution is happening all around us and we don’t “see” it because it takes a long time.

So the number of species you see around you is what the world can sustain. Maybe a few more or a few less might be possible, but basically we’re seeing a kind of steady state – the species we see all have “niches” and they’re fine. They are able to exploit their surroundings to live. There are relatively few places on the earth that can’t support life. The middle of the desert or right at the bottom of the ocean. But there are some extreme places that still do. Those animals are there because they’re able to be – they are able to live and have kids. That’s all you need. So a species exists because the animals are able to breed.

We have to worry about any big disturbances – that might destroy where a species lives. Then we destroy its niche and we could wipe out the species. The world has existed for a lot longer than we have, and if we start losing a lot of species that might have bad unintended consequences, besides making the world a lot less interesting to live in. So cutting down forests and polluting rivers is a bad idea.

Life first evolved in a warm soupy pool of water (or at the very depths of the ocean) somewhere on earth about 3.8 billion years ago. When that first type of life emerged, there was only one species. But as this life form multiplied, each individual was slightly different to the next one. This is because little errors can occur when DNA copies itself during cell division.

Some of these life forms might have been different so that they could live in a slightly warmer temperature, so they might have moved to a warmer part of the pool (or the ocean). If these “warm” life forms lived away from the others for long enough, soon the two groups would be so different that they would be different species. This is the process of evolution by speciation (how different species form).

This is just an example of speciation, but it happens with all different plants, animals and bacteria. If a group of animals can live in a different place or under different conditions to another group of animals in the same species, it means they don’t need to compete for space and food anymore. There are so many different places and conditions for animals to live in, and by evolution, they have changed into different species to be able to live in all these places

Because there are so many different types of environment on Earth.

In order to survive, each species needs to find a habitat which provides it with enough food, space and shelter to live and reproduce. There is a huge difference in the conditions of the ocean compared to the desert and a forest compared to a lake. Most species can survive in one of these environments but not another.

If all the animals on Earth could live in a rainforest but nowhere else, then there would be all these other areas of the Earth without anyone to fight for territory or food, or to eat you. The animals in the rainforest, meanwhile, are all be competing with each other for survival, which does not lead to a pleasant and prosperous lifestyle. If one of these species developed a mutation (a change in the DNA) which allowed it to live outside the rainforest (eg. better lung capacity so it can live at high altitude, or longer fur so it can live in cold climates) then it could move to the new area. There would be nothing else eating its food or trying to eat it, and the species could get busy multiplying itself.

This is basically what happened during evolution. We all started out as single-celled swamp-dwellers. After becoming multi-cellular fish type things which could live in these lakes, some of the fish-things mutated so they could live on land. Nothing else could live on land so they had a huge advantage. After a bit longer different types of land-dwellers would have emerged as more mutations occurred, allowing the different species to spread to new environments.
After a very long time there would have been millions of species in millions of different environments which each was specially suited to. Many of these have since died as the conditions changed and the species was no longer successful, which leaves a gap for a new species to emerge.

All of this is still happening now, but very slowly, so we couldn’t see it within our lifetime. Or even the lifetime of your entire traceable family tree. What we are seeing is the extinction of many species as their unique habitats are destroyed and they are not adapted to live anywhere else.

Earth's species have more in common than previously believed

Credit: CC0 Public Domain

The Earth hosts an abundance of life forms—from well-known animals and plants to small, more hardy life forms such as archaea, viruses and bacteria. These life forms are fundamentally different all the way down to the cell level—or so scientists thought.

Now, an international team of researchers has analyzed the proteins found in 100 species—from bacteria and archaea to plants and humans. It is the largest protein mapping ever to be conducted across different species.

They have learned that these life forms have a number of common characteristics. The study is a collaboration between researchers in Professor Matthias Mann's group in the Novo Nordisk Foundation Center for Protein Research and the Max Planck Institute of Biochemistry. It has been published in the top scientific journal Nature.

"We have mapped the proteins, together called the proteome, of 100 different species. And it is obvious that they are extremely different. At the same time, though, they have more in common than we thought. In all these life forms, a large share of the proteins focus on metabolism and on maintaining a protein balance," says Professor Matthias Mann.

Doubling of Experimentally Confirmed Proteins

Previously, researchers were mainly interested in the DNA of various organisms, for example, how much genetic material humans share with different animals. However, with advancements in the technology used for studying organisms at molecular level, researchers have turned to proteins, the workhorses of the cell.

"A common characteristic of all these life forms is the fact that a high percentage of their proteomes focus on maintaining a sort of balance, what is called as homeostasis. Another common characteristic is the fact that a large share of the proteins help to generate energy. Even though the ways in which this is done differ—from photosynthesis to carbohydrate burning," says Alberto Santos Delgado who during the studies was employed at the Novo Nordisk Foundation Center for Protein Research.

The researchers have used an advanced technology called mass spectrometry to study all 100 species. The technology enabled them to double the number of proteins confirmed experimentally.

Previous research has predicted how many and which proteins exist based only on the genetic code and bioinformatic calculations. However, the new protein mapping has provided actual data on the existence of a very large number of new proteins.

Machine Learning Can Reveal New Correlations

"Our work connecting quantitative mass spectrometry-based proteomics with database resources has resulted in a data set of eight million data points with 53 million interconnections. We made all the data publicly available, enabling other researchers to use it to identify new correlations. New technologies enabled by machine learning are on the rise and we expect those to benefit from the large and uniform dataset we provide publicly," says Ph.D. Student Johannes Mueller from the Max Planck Institute of Biochemistry.

The researchers at the University of Copenhagen focussed on data processing and bioinformatics analysis, while the researchers at the Max Planck Institute of Biochemistry in Munich focussed on mass spectrometry.

On the website Proteomes of Life, the researchers will make all data from the project publicly available.


  1. Mum

    It is a pity that I cannot speak now - I have to leave.I will be back - I will definitely express my opinion on this issue.

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  6. Gunther

    I can't take part in the discussion right now - there is no free time. I'll be back - I will definitely express my opinion.

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