Is evolution a fact? [closed]

Question

Richard Dawkins in one of his videos says that Evolution is a fact and not just a theory.

He goes on to say that man and chimpanzees both evolve from apes. Is this correct (Is evolution a fact and did humans & chimps evolve from apes)?

Answer 1

A tiny bit of terminology

Fact

• In popular culture, the term fact means "something that is true". I would consider a theory as being the closest concept in science to what is called a fact in the population culture.

• In natural sciences, the term fact is rarely used but would have the same meaning than the one in popular culture. The reason we are not often using this concept is that in science (nor in any other field of knowledge) one can never definitely know the truth. We can only have evidence that are congruent with a hypothesis or body of statements. In such case we talk about theory (see below).

Theory

• In popular culture, "theory" is used to mean what the natural sciences call a "hypothesis."

• In the natural sciences, a theory is a body of thoughts/statements that is very well supported by loads of evidence. In science, a theory is not a hypothesis. For example: Theory of evolution, Theory of general relativity, transition state theory, etc. _{Note by the way that various definitions of theory are in use (ref.). The below answer respects the definition that I gave above.}

The scientific terminology presented above is actually a matter of philosophy and not science. If you need more information about the definitions of "theory", "fact" and other related terms, you may want to ask on Philosophy.SE. Stephen Jay Gould summarized the concepts of theory and facts nicely when saying

[..] facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas that explain and interpret facts.

In the answer below, I am using the scientific terminology.

Your questions

Is evolution true?

Evolution is what is called a theory in natural science (The Theory of Evolution a.k.a. modern evolutionary synthesis), and it is extremely well-supported. Evolution is NOT a hypothesis. In other words, we have a lot of supporting evidence that living beings have evolved and are evolving.

Did both humans and chimpanzees evolve from apes?

Humans and chimpanzees are apes (great apes to be more accurate). Both humans and chimpanzees evolved (and are still evolving) from a common ancestor who already was a great ape. We have a lot of evidence to support this common ancestry.

What does the theory of evolution say?

Understanding Evolution (by UC Berkeley) is a short and introductory course to evolutionary biology. Of course, there exist other good sources of information online such as Evolution and the tree of life by Khan Academy.

We have a number of posts providing book recommendations for

• General biology (Books for beginners and Introductory biology text for an outsider)
• Intro to evolutionary biology (Text Book Recommendation: Organic Evolution and Introductory books about evolution)
• Intro to evolutionary genetics (Books on population or evolutionary genetics?)

You will also find a lot of introductory posts on biology.SE such as for examples:

• Why do some bad traits evolve, and good ones don't?
• Is there a biological mechanism for evolution encoded into our DNA?
• Does it make sense to classify all humans in a single species?
• Why is a heritability coefficient not an index of how “genetic” something is?
• How could humans have interbred with Neanderthals if we're a different species?
• If dinosaurs could have feathers, would they still be reptiles?
• Why does evolution not make our life longer?
• Why don't mammals have more than 4 limbs?
• How to define “evolution”?
• How did some humans evolve to be white?
• Who are humans' closest relatives, after primates?
• Did cats evolve from monkeys ? or vice versa?
• Why do the ancestors of birds still exist?
• How does Natural Selection shape Genetic Variation?

What are the evidence?

Demonstrable and repeatable examples of evolution lists sources that list evidence. There are probably thousands of pieces of evidence listed in total, all explained in lay terms with links to the original article. Of course, this is just a small sample of the evidence we have.

The post Is there any biological evidence that is not suggestive of or seems to disprove evolution? might be of interest too.

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Thanks to @CortAmmon's comment for correcting a very poorly phrased sentence.

Answer 2

A scientific fact is something that is true. A fact cannot be proven false. This is no different from the common usage of the word. However, in science, we often do not definitively know what is true. Therefore, scientific facts tend to be observations based on specific evidence.

A scientific theory is a well-supported and rigorously tested explanation of a phenomenon.

These definitions are consistent with those given by the National Academy of Sciences.

In science, we use a body of facts to arrive at a theory. Science is a discipline of likelihoods, confidences, and uncertainties. We gather evidence to improve our confidence and minimize the uncertainty of a theory. This is how we arrive at a very likely explanation, such as the theory of evolution.

But we do not draw facts from theories - we draw theories from facts.

Answer 3

Tl/dr: No, evolution is not a fact (unless your definition of fact defines evolution to be a fact, in which case it is a fact...). And if that phrase ruffles your feathers, it suggests you should read the rest of this answer. I usually wouldn't put the Tl/Dr here on this particular topic, but apparently people have been unhappy with my answer being burred in it.

Richard Dawkins is a very loud personality who has demonstrated a consistent interest in silencing dissenting opinions.

Evolution is a theory which seeks to explain the world and predict future events. It has entered a special class of theories where we have observed so much evidence to suggest that theory accurately models our world that people find that society operates smoother if we pretend that it is 100.00000% true. In reality it is not. It could be wrong. However, we in society have a choice: we can pretend it is 100% true, or we can acknowledge that there is a tiny shred of doubt that must exist due to the nature of the scientific process. In general, we have found the negative impact of pretending it is "true" is much smaller than the negative impact of people hearing that there's some doubt and presuming there is more doubt than there really is.

In my opinion, what has made evolution so tricky in the political world is that those who understand science well enough to actually understand what is meant by the statistical data captured to support evolution are generally happy "rounding up" evolution to 100% true, because they understand how to use the statistics, and there really hasn't been enough of an advantage to keeping track of the sliver of doubt. Science always has a sliver of doubt, so they're always watching out for it anyways (no scientist is going to say "you can't be alive" to a new species because it didn't fit the model). Those who find enough value in that doubt to take the time and energy to call it out by name typically do not have enough of a science and mathematics background to really comprehend what that level of doubt is, or how to manipulate it, so there is a trend of them doing so poorly and coming to very questionable conclusions. Probability is full of such cruel scenarios, such as the prisoner who runs at a wall repeatedly, once every second, and you may be asked to calculate how long it will take for him to have a 50% probability of quantum tunneling through the wall to escape. Depending on the numbers, that timeframe may be more or less than the heat death of the universe, but the probability is absolutely there, and its never zero! (hint: if you get in prison, try to get out on good behavior... the running at the wall solution isn't the best approach)

In the end, it's all linguistics. An interesting tangent is the use of "fact" in philosophy. In philosophy, "fact" doesn't always mean exactly what you may intuitively think it does. Many philosophers declare that an auditory or visual hallucination is a "fact" because it meets the philosophical definition of "a state of affairs," lending itself to strange phrasings such as "a fact about something which is not real" and other linguistic oddities.

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EDIT

I pose a statistics question to you. Your answer to this statistics question states how you approach the definition of some very key words, so the answer as to whether evolution is true or not will depend on them.

I flip a coin multiple times. There's no reason to presume it's a fair coin, so no reason to presume P(heads) = 50% like in so many coin tossing problems. I flip the coin a million times. It lands heads every time.

I am about to flip the coin again. Is the statement "The coin will land heads up" a true statement?

If you answer "no," because the coin flipping problem is in the domain of statistics, and statistically prior observations do not define the results of the next flip (though they obviously suggest at it), then your answer should be "evolution is not necessarily true," There's an extraordinary body of evidence supporting the claim statistically, so we can certainly make the claim "we are quite confident that evolution is true," but we cannot take the leap to declare it is "true" because we are basing our position in the statistics that form the foundation of modern science.

On the other hand, if you answered "yes," then you may state "evolution is true" to your hearts' content. You have made the presumption that a bunch of evidence is the same as truth. Of course, you make that statement without the backing of mathematics, so you don't actually have any proof to back your statement. You are, in fact, making as religious of a statement as the claims that evolution is false made by creationists. You are declaring something to be true, simply because you believe it to be true.

Why do I make such a big deal about this? Because claims such as "evolution is true" are making it harder and harder for people who do not believe in science religiously to accept the results of science. If I can talk to a creationist about evolution, I can get them to understand our POV in about 5 minutes... but it takes 30-50 minutes of battling them to get there. Why? Its because they have been told over and over a point of view about what science claims which is not technically accurate and conflicts with their beliefs. The overstatement of the confidence in evolution from "very confident" to "100% proof positive without a doubt confident" actually gets in the way.

So please, decide which version of the word "true" you wish to use, the mathematical one or otherwise, and make your statements accordingly. Just know that the mathematical rigor behind the study of evolution is only applicable if you're using mathematic's definition for key concepts like truth.

Answer 4

None of the answers so far have really provided much evidence, so here is a small sample of the peer-reviewed articles, based on genomic information that provides the facts that we know so far that provides us with the evidence to draw the conclusions that we do.

Morris Goodman, The Genomic Record of Humankind's Evolutionary Roots, The American Journal of Human Genetics, Volume 64, Issue 1, January 1999, Pages 31-39, ISSN 0002-9297, http://dx.doi.org/10.1086/302218.

• Provides an overview of the sameness of the Human and Pan (chimpanzee and bonobo) genomes and also goes through other similarities such as extended gestational and postnatal upbringing for humans and Pan. Discusses similarities uncovered through observational studies that "chimpanzees are emotionally complex and intelligent."
• It goes on to discuss phylogeny, different classifications and the history of some of the branching of species.

The Chimpanzee Sequencing and Analysis Consortium, Initial sequence of the chimpanzee genome and comparison with the human genome, Nature 437, 69-87 (1 September 2005) | doi:10.1038/nature04072; Received 21 March 2005; Accepted 20 July 2005 Here the abstract probably best defines the contents of the journal article.

Here we present a draft genome sequence of the common chimpanzee (Pan troglodytes). Through comparison with the human genome, we have generated a largely complete catalogue of the genetic differences that have accumulated since the human and chimpanzee species diverged from our common ancestor, constituting approximately thirty-five million single-nucleotide changes, five million insertion/deletion events, and various chromosomal rearrangements. We use this catalogue to explore the magnitude and regional variation of mutational forces shaping these two genomes, and the strength of positive and negative selection acting on their genes. In particular, we find that the patterns of evolution in human and chimpanzee protein-coding genes are highly correlated and dominated by the fixation of neutral and slightly deleterious alleles. We also use the chimpanzee genome as an outgroup to investigate human population genetics and identify signatures of selective sweeps in recent human evolution.

Feng-Chi Chen, Wen-Hsiung Li, Genomic Divergences between Humans and Other Hominoids and the Effective Population Size of the Common Ancestor of Humans and Chimpanzees, The American Journal of Human Genetics, Volume 68, Issue 2, February 2001, Pages 444-456, ISSN 0002-9297, http://dx.doi.org/10.1086/318206. From this paper we are given evidence of the following

To study the genomic divergences among hominoids and to estimate the effective population size of the common ancestor of humans and chimpanzees, we selected 53 autosomal intergenic nonrepetitive DNA segments from the human genome and sequenced them in a human, a chimpanzee, a gorilla, and an orangutan. The average sequence divergence was only 1.24% ± 0.07% for the human-chimpanzee pair, 1.62% ± 0.08% for the human-gorilla pair, and 1.63% ± 0.08% for the chimpanzee-gorilla pair.

The key to this evidence is this; "we selected 53 autosomal intergenic nonrepetitive DNA segments from the human genome and sequenced them in a human, a chimpanzee, a gorilla, and an orangutan."

The significance of this lies in the fact that intergenic non repetitive DNA has very little, if any, selective pressure on it to maintain its sequence. Assuming that random mutations do not significantly alter gene expression, then there is no reason that there should be such high rates of homology, unless we are closely related to these other species on an evolutionary time scale. That being said, if some of those changes do have modest effects on gene expression, whether they are timing of expression in development, levels of expression, or tissue specific expression, then those can result in the differences we witness in the modern versions of the species alive today.

It would not be too surprising to find this level of homology in coding regions of genes across mammals, especially if we looked at the amino acid homology of the proteins encoded by these genes, as mutations in these genes would be under evolutionarily selective pressure. But to see homology this close in DNA in between genes suggests a very close relationship.

Philipp Khaitovich, Wolfgang Enard, Michael Lachmann & Svante Pääbo, Evolution of primate gene expression, Nature Reviews Genetics 7, 693-702 (September 2006) | doi:10.1038/nrg1940

Finally this paper gives an explanation of how gene expression can account for the evolutionary differences seen between Humans and other primates. It is unfortunately behind a pay wall, but here is the abstract of the article to give a sense of what it has to say on the matter.

It has been suggested that evolutionary changes in gene expression account for most phenotypic differences between species, in particular between humans and apes. What general rules can be described governing expression evolution? We find that a neutral model where negative selection and divergence time are the major factors is a useful null hypothesis for both transcriptome and genome evolution. Two tissues that stand out with regard to gene expression are the testes, where positive selection has exerted a substantial influence in both humans and chimpanzees, and the brain, where gene expression has changed less than in other organs but acceleration might have occurred in human ancestors.

Zoonoses and Host / Viral Pathogen Interactions

I should also add that another way we can gauge evolutionary closeness is through host viral pathogen relationship. Viruses have evolved to have a high degree of specificity in their mode of infection, and what works for a virus in humans may be harmless to dogs or birds or mice because the cell surface proteins that viruses exploit to infect the cells of multicellular organisms have a greater degree of difference the further away species are evolutionarily from the last common ancestor. And while there are cases where there will be intraspecies differences that afford immunity, such as the CXCR4 mutation which provides some level of resistance to HIV-1, for the majority of the species, the virus will be able to infect hosts of that species.

Many zoonoses cannot be transmitted between distantly related species. With that in mind, Chimpanzees can catch most all diseases that humans carry and vice versa. Simian Virus 40 has been implicated in human cancers and research has shown that the Human Immunodeficiency Virus originated in Chimpanzees and is called the Simian Immunodeficiency Virus, though the virus proves to be harmless in Chimpanzees.

In contrast cats have the Feline Leukemia Virus, which is highly contagious and can be passed between cats and cause leukemia, but cannot infect humans. Dogs and cats can be infected with life threatening Parvovirus, but humans are not at risk of this infection.

So if you are skeptical of the genomic evidence, then trust the viruses, because they will tell you how closely related organisms are by how effective they are at infecting different species.

Answer 5

It is easily observed that populations of organisms change over time, both phenotypically and genetically. With some organisms we can observe this over a few days of observation; with others we can use historical records. Therefore, evolution is an observed fact.

However, most people, by "evolution", are actually thinking of "the theory of evolution through natural selection", which is a theory. In fact, there are a number of explanations for why and how populations change over time. These include the theories of natural selection, of neutral and nearly-neutral drift, of sexual selection, and so on. These are of course theories, albeit (for the ones I list here) enormously well-supported theories.

You can compare to gravity. If I drop an apple, it will fall to the ground; if I watch that, it is an observed fact that the apple fell, just as it is an observed fact that the population of viruses I looked at last week changed their genetic composition (that is, evolved) over that period. Newton's theory of gravity is a theoretical attempt to explain why the apple fell. Like Darwin's theory of natural selection, Newton's theory was wrong, but useful, and like natural selection, other theories have come along to improve on Newton. (Unlike Newton, Darwin seems to have been almost entirely right, so that the new theories have supplemented but not replaced his theory.)

So yes, evolution is a fact.

Answer 6

I am not very happy with most of the answers here as they seem to be too ideologically motivated and not so much about scientific reasoning. So I decided to give it another try.

Is Evolution really a fact and not just a theory?

If this is too long for you, let me just say this:

Evolution is an existing phenomenon. There is variation, there is selection and inheritance of traits. This has been studied and there is no scientific doubt that evolution is a process that is happening now and all the time.

Note that I intentionally bolded the word scientific. The rest of may answer will be mostly about science.

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In science just a theory is not meant in a pejorative way. Everything that can be disproved, but scientist have not been able to disprove is a theory. The important part is that it must be possible to disprove theories by scientific methods.

In a way you can think of the principle of gravity also as just a theory. If you happen to find mass that does not get attracted by other mass, you would be able to prove Newton wrong. But the evidence of the existence of gravity is so overwhelming that I would not spend too much energy on that :)

So - from a scientific view evolution is a theory with overwhelming scientific evidence. There is so much evidence that among scientist this debate is settled, just like the theory of gravity. The vast majority of the scientific community accepts the theory of evolution as the theory which is most probable to shape life here on earth.

But the attentive reader may have spotted a problem in the last sentence: There is an unlimited number of theories that can explain how the life shaped to a way that we can admire it today.

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Long ago people realized that the most important part of a scientific theory is that it must be somehow possible to disprove it. Of course we can create a theory that contradicts gravity where a green-yellowish rectangular slime pushes objects together. Scientists will be able to disprove as long as it is falsifiable.

But if we now give the slime the sneaky attribute that it escapes human senses, we have a perfectly valid theory that cannot be disproved. So if someone would ask you if it is 100% sure that Newton's theory of gravity is correct, what would you answer? You cannot simply dismiss the theory of the green slime, can you?

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Okay back to science. Science basically tells you: You can and you even have to dismiss any theory that is not falsifiable. Theories that cannot be disproved are not valid in a scientific sense. Back to your question:

He goes on to say that man and chimpanzees both evolve from apes. Is he 100 % correct?

Is he 100% correct? - Certainly not, we can make a slimy theory that works as well.

Okay, so let's put it in a different way: Is he 100% correct in a scientific sense - This we cannot answer. There may be many now unknown scientific theories that explain life in its current form equally well. But at the moment we only have evolution.

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So why then are scientists so sure? Why does Richard Dawkins tell us all the time that evolution is real?

Well scientists are pretty convinced because of two things: Firstly, a lot of scientific evidence has been collected to support the theory of evolution. There are fossils, there is genetic information, there are experiments that validate certain aspects. But what is even more important: Until now nobody could come up with an experiment disproving the key aspects of the theory of evolution.

There is a second important point here: At the moment we don't have any competing scientific theory. The theory of evolution in science is a little like olympia with just one participant. If someone wants you to bet on the winner, what would you do?

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I acknowledge that there are non-scientific theories that can explain all aspects of existence equally well, but I want to strongly emphasize that these are NOT scientific theories. You do not have to accept science as an important explanatory system. But if you do, I hope I could convince you that scientific reasoning of scientists regarding evolution makes sense and although there is no way to quantify this believe in 90%, 99%, 99.9% or 100%, there is overwhelming evidence that make people like Richard Dawkins such firm proponents of the theory of evolution.

Answer 7

Evolution is most real. Have a look at this Wicked Cool Phylogenetic Tree from wikipedia:

What it implies is that there is one common ancestor.

EDIT:

I remember my professor telling me that phylogenetic trees work like a cot mobile. During our lectures on phylogenetics he would on occasion pick up the chalk and make crude drawings of three fish of dissimilar sizes on the blackboard. Always three fish. He would then tell us about how the bigger fish eat the smaller fish. The way I interpreted this is that natural selection played a role in what we observe today as protein to protein or gene to gene similarities. That is what this phylogenetic tree represents. I think my professor made the analogy to mobiles not because they go in circles but rather because phylogenetic grouping can be monophyletic where an ancestor with all it's descendants are considered a group, paraphyletic where an ancestor but not all it's descendants are considered a group, or polypheltic where the common ancestor is not taken into account. I pasted this phylogenetic tree with a monophyletic view on the matter.