Freedom had been hunted round the globe; reason was considered as rebellion; and the slavery of fear had made men afraid to think. But such is the irresistible nature of truth, that all it asks, and all it wants, is the liberty of appearing.
~ Thomas Paine, Rights of Man, 1791 ~

Sunday, November 20, 2016

What is the evidence for evolution, and why do people believe it?

In this article I want to list some of the reasons why so many people, including the vast majority of scientists, believe in evolution.

Even if you are a creationist, it's important to understand not only what other people believe, but also why they find it compelling. If you cannot fathom how any sane, rational person could believe in evolution, then maybe what you call 'evolution' is not actually what people believe. Maybe they believe something else, instead.

So let's take a look at some lines of evidence...


Fact: Fossils are found in layers of sedimentary rock, but not all fossils are found in all layers. Deeper layers generally indicate an earlier time period and vice versa. Less complex fossils are always found in earlier layers, while more complex fossils are always found in more recent layers. This is the same for fossils of plants as well as animals. Most of the fossils in earlier layers belong to species that are now extinct.

Fossils are a fascinating subject all of their own. Paleontologists study fossils to learn about what the world looked like in the past. We understand how fossils are formed, and we can determine a great deal of information from not only the fossils themselves, but also where they were located.

One of the most striking facts about the fossil record is in the way fossils are layered in sedimentary rock. Due to the way these sediments were laid down, we can conclude that, generally speaking, lower layers formed before higher ones. The study of these geological layers is called Stratigraphy.

What we find everywhere in the fossil record is that the more recent layers contain fossils of more complex life forms, while older layers contain fossils of less complex life forms. This presents an immediate puzzle. What does this tell us about the history of life on earth?

The most natural explanation is that earlier life forms were indeed less complex and that living organisms became more complex over time. Not individually of course, but rather successive generations of organisms became gradually more complex than the last. We can also work out roughly when each sedimentary layer was formed, and thus calculate a rough timeline of the development (or, 'evolution') of life on earth. When scientists talk about fossils being millions or billions of years old, these are not wild guesses. They are actual measurements using very precise techniques. More on that later.

For creationists, however, the difficulty is clear. At a minimum, they must reject any notion of a long timeline of events (depending on their view of creation). Some suggest that the layers were all laid down during Noah's flood. They suggest that the layers were formed through cataclysmic events, and that the reason for the layering of fossils from least to most complex is due to the more complex creatures being more able to reach higher ground during the early stages of the flood.

The shortcomings of this answer should be fairly obvious, but I'll list just two major flaws. Perhaps you can find more. Firstly, studies of the Grand Canyon reveal nearly 40 layers, including signs of erosion between some layers. This can only be explained by many separate geological events, over a very long period of time, with additional long periods in between. Secondly, it's simply absurd to think that dinosaurs (including ones that could fly) failed to beat sloths to higher ground. But in case you do think it's plausible, I'll leave you to ponder how all of the plants and trees managed to pull off the very same feat. Then there's the fact that fossils of Kangaroos are only found in Australia...

Radiometric Dating

Fact: Despite what creationists may tell you, Radiometric Dating methods, including Carbon Dating, are reliable. We know this because they have been tested extensively on samples of known age, and also compared against other methods such as ice cores and tree rings. Not only do scientists know they work, they understand how they work, and the limitations of each method.

Fact: Most fossils are not dated using Carbon Dating. This is because Carbon Dating is only reliable for biological organisms up to 50,000 years old. It is not used on rocks, and organisms older than 50,000 years old, because they don't contain any (original) carbon.

One common tactic of creationists is to insist that while we have a huge array of evidence from the fossil record, we have no way of knowing how old each fossil really is. This is quite simply dishonest. You've probably already heard of Carbon Dating and if you're a creationist, you probably already "know" that it's not reliable. But if so I'd like to ask you to reconsider, and I will present what I think is some pretty compelling evidence.

The first thing to point out is that, despite what you may have heard, Carbon Dating has been rigorously tested, including against samples of known age. Scientists are not stupid. Further, in almost all cases, several samples are collected from different parts of an organism. If Carbon Dating produced wildly inaccurate or random results, it would be difficult to explain how the results from multiple samples agree. Most (if not all) of the creationist claims about unreliable results from Carbon Dating are a result of contamination or creationists who didn't know what they were doing.

The second thing to point out is that Carbon Dating only works for samples up to around 50,000 years old. How do we know that? Well, because again scientists test it extensively to determine how accurate it is, and where it can or cannot be used. They also understand how and why it works, and they can predict how long it takes for the original Carbon-14 in an organism to decay.

What does this mean? Well, for the majority of fossils, Carbon Dating isn't used. That's because for fossils that are millions of years old, there's none of the original carbon left in them. But how do we know they are millions of years old? Well, we can determine when the surrounding sedimentary rock layer was laid down.

One method is Radiometric Dating, which works similar to Carbon Dating but using other isotopes that decay more slowly. Has it been thoroughly tested? Yes.

Is it reliable? Consider this. Radiometric Dating can be used with several different isotopes, all with different decay rates. Yet all of the methods agree, not only with each other but also with other methods as appropriate, including ice cores, and tree rings.

Some Christians have argued that something may be slowly changing with time so all the ages look older than they really are. The only two quantities in the exponent of a decay rate equation are the half-life and the time. So for ages to appear longer than actual, all the half-lives would have to be changing in sync with each other.
Radiometric Dating: A Christian Perspective

Have radioactive isotopes been changing? No, they haven't.

The simple fact is that scientists don't just cherry-pick data and use random methods to arrive at some desired conclusion. That's just not how science works. The various dating methods do rely on some assumptions, but even those assumptions can be (and are) tested. We know the methods work, and we also know their limitations. I'd encourage you to research this directly from the scientific sources, rather than creationist websites. By all means read the creationist websites as well, but check all of their claims against the data. You'll even find plenty of responses to creationist claims within the scientific literature.

By the way, the age of the Dead Sea Scrolls was determined via Carbon Dating.


Fact: Humans share at least 95% of our DNA with chimpanzees.

Fact: Some viruses insert their DNA at random positions in the genome of the host, which, if it affects the germ cells, can be passed on to descendants. There are several instances of such viral insertions in exactly the same locations in both the human and chimpanzee genomes.

Fact: By comparing the DNA of various animals and using markers such as insertions of viral DNA, scientists can plot the family tree of these animals. When they do this, it matches almost exactly with the relationship structure that had already been determined via comparative morphology. Such a match is difficult to explain if all animals do not share common ancestry.

The evidence just from fossils is probably enough on its own, but there is another significant piece of evidence that points strongly to evolution. Our DNA. Our genome consists of genes, which are contained in long strands of DNA called chromosomes. These genes and other molecular codes in our DNA determine how an organism grows, from a single cell into something far more complex.

Since the Human Genome Project was completed in 2003, we now have a map of the entire human genome. Since then several other genomes have also been sequenced, from chimpanzees to mice, and even bacteria. We now know that humans are all 99.9% alike in their DNA. That is, the many differences between all humans comprises only 0.1% of our genome.

In contrast, humans share about 95% of our DNA with chimpanzees (or more, depending on how it's compared). The more distantly related the animal, the less DNA we share in common.

The similarity between genomes on its own is not sufficient to prove common descent. Creationists like to appeal to a common designer to explain this detail, arguing that God would have reused components in creating each species.

But there is some evidence in the genome that makes common design extremely unlikely.

There are mistakes in our genome, caused by ERVs (Endogenous Retro Viruses) and transposons (similar to viruses, but they only replicate in the genome of the host). These result in viral DNA being transcribed into the genome essentially in a random location. If they happen to occur in germ cells, they are passed on to offspring, including subsequent generations.

As explained above, finding the same transposon in the same chromosomal location in two different organisms is strong direct evidence of common ancestry, since they insert fairly randomly and generally cannot be transmitted except by inheritance. In addition, once a common ancestor has been postulated that contains a certain transposition, all the descendants of this common ancestor should also contain the same transposition. A possible exception is if this transposition were removed due to a rare deletion event; however, deletions are never clean and usually part of the transposon sequence remains. Using the same principles behind DNA fingerprinting, biologists have used transposons, pseudogenes, and endogenous retroviruses to demonstrate that many species are genetically related, such as humans and other primates.
Most importantly, in the human α-globin cluster there are seven Alu elements, and each one is shared with chimpanzees in the exact same seven locations (Sawada et al. 1985).
29+ Evidences for Macro Evolution

This last part cannot be overstated. Scientists understand the mechanism for how these retro-viral insertions end up in the genome. They can identify several of them in the same locations in both chimpanzees and humans (and likewise there are such similarities between other closely-related species). The same methods can and have been used in paternity cases and in criminal forensics. The natural explanation is that we share these same viral DNA sequences in the same locations because both chimpanzees and humans descended from an earlier ancestor that was infected by the virus. Scientists can even use these genetic markers to trace different lineages, including human ones.

All a creationist can do in the face of this evidence for common descent is claim that "God just happened to do it that way". And indeed the same could be said for any evidence, which makes creationism unfalsifiable, and therefore unscientific.

One last, but significant piece of genetic evidence comes from what we find when we use the genetic similarities to map relationships between species. When all of the sequenced genomes are fed into a computer and analysed, the resulting family tree corresponds almost exactly with what had already been determined through earlier methods such as morphology. Charles Darwin, who published the theory of evolution, had no knowledge of DNA, and yet more than 100 years after his work was published, evolution has been confirmed yet again in spectacular detail.

It is difficult to imagine how all of the above could be true, if we were all specially created by an intelligent designer. At the very least we would need to accept the idea that the designer just happened to create all species in such a way as to make them appear to have evolved through common ancestry.

The far simpler, and more natural explanation is that we really did evolve through common ancestry, whether there was any designer behind it or not.

Other Evidence

I've barely scratched the surface of the available evidence for evolution. However even just what I've outlined above is enough in my view to demonstrate that evolution has occurred. We could talk about the proposed mechanisms by which it has taken place, but that's a separate discussion. Scientists have a good understanding of the basic mechanisms behind evolution, including how and why it works, but there is still a lot we don't know. But the fact that it has occurred is undeniable given the copious available evidence.

Some creationists try to point to gaps in our understanding as evidence that evolution isn't true, but this reasoning is flawed. You may not understand how an aircraft works, but seeing one flying through the air is enough to conclude that it does. Likewise even if we don't understand every minute detail about how evolution works in every case, we can see the evidence of change over time (or 'descent with modification') and conclude that it really did happen.

If you do want to see a more comprehensive list of evidences for evolution, I highly recommend reading this article: 29+ Evidences for Macro Evolution.

Has speciation been observed in the lab? Yes, it has.
Has speciation been observed in nature? Yes, it has.

Are there any transitional fossils? Yes, there are. And here's another list.

You can also find many answers to creationist claims here: Index to Creationist Claims.

In my experience (and indeed this was true for me also) the two main reasons why people deny evolution are (1) a general lack of education on the subject, and/or (2) a prior commitment to (religious) beliefs that were inherited during childhood.

As I mentioned at the beginning of this article, if your view of evolution is such that no sane, rational person could possibly believe it, then I would strongly suggest to you that perhaps no sane, rational person does believe what you think evolution is. Perhaps they believe something else instead. It's time you read some more about what scientists really do believe, and what the evidence shows. You're not going to get that from second-hand sources.

Remember that the truth does not always conform to your existing beliefs. Any good scientist or truth-seeker knows that they should follow the evidence wherever it leads, regardless of whether the conclusion is comfortable. If you've previously accused others of simply believing what they want to believe rather than honestly following the evidence, then it's important that you don't make that same mistake yourself. Lying to others is dishonest. Lying to yourself is stupid.

Good luck in your search for truth.


  1. Easy answer. About 6,000 years ago, the earth was destroyed by some unknown cataclysm and then re-created as given in Gen 1. This is proven in verse 2. Not only does it say "waste and desolate" (cp. Jer 4:23), but it also says, "face of the waters." The waters were present before the Creation. Psa 104:6 describes them as "standing above the mountains." On day 2 and day 3, they evaporated and revealed dry land. So the mountains were also present. The light on Day 1 was probably from the sun, but it was blocked by clouds. It was finally revealed on the fourth day.

    Theory is that whatever existed prior was destroyed and a new earth was created in its place. The animals and even man that were created after the destruction may have existed prior to the destruction and were simply re-created. This is not so far-fetched since there was the flood that pretty much did the same thing. There are also prophecies of a new earth and new heaven after the millennial reign.

    1. I think you need to re-read what you wrote.

      If the earth was destroyed and re-created just 6000 years ago, why do we have evidence of nearly 40 strata in the Grand Canyon?

      Then you said:
      "The animals and even man that were created after the destruction may have existed prior to the destruction and were simply re-created."

      But if there was any such destruction, we'd have no way to tell what existed before. We would only see what exists now. The fossil record suggests a long history of evolutionary change on earth. Those fossils shouldn't exist if the earth was destroyed only 6000 years ago.

      You said "Easy answer" - but I can't see what your comment actually answers. How would it explain the shared genetic defects between humans and chimpanzees, for example? And how would it explain the gradual change over many layers in the fossil record?

      You mentioned the flood. Can you point to which of the layers in the fossil record belongs to this flood?

      And my final question: What evidence would you expect to find if there was no worldwide flood, and if the earth had not been destroyed and re-created 6000 years ago?

  2. Aaron, quoting from a book of fables is hardly concrete evidence to refute the facts of evolution. As science discovers more proof, the religious will become more desperate and perform increasingly complex mental gymnastics to try and explain it all away.
    Surely if you are seeking the truth then you should leave no stone unturned, not just look under the couple that you know will back up what you want to believe.

    1. I'm pretty sure Aaron doesn't think he's quoting from a book of fables. If his view was actually true then quoting the Bible probably makes sense, although quoting it to other people who don't share his view is probably a waste of time.

      In any case I'd still have to question how anyone could possibly determine that (a) a god exists and (b) that it is the author of the Bible. And even if that were true, that wouldn't prove that the Bible was true.

      If there was a god who wrote a book but the book disagreed with basic observations from nature/reality, then the book would still be wrong. There's no way around that.

      But instead we have a book written in the Bronze/Iron age, containing ideas that were popular among many ancient civilisations of that time, including slavery and genocide, and attributing successes in war to their national deity and blaming losses and weather patterns on angry gods. The creation stories (yes, there are multiple, and they disagree) are similar to those of other nations at the same time, and there are human fingerprints all over the book. Those who see divinity in it are those who were already convinced the book was divine. It's no different for any other religion either.

      I do want to reiterate Mark's last sentence. If you are seeking truth, try to understand points of view you disagree with, to see why people hold them. That goes for us as well. It's why I'm always happy to discuss this stuff with believers. They claim to know there's a God, and that the earth was specially created, and I want to know how they know. I also want to know what makes them so sure about their beliefs. It could be that I'm wrong - and if so, I want to find that out and correct my beliefs.

  3. Steve/Aaron
    What Aaron is doing is using that well worn strategy: "But it fits!", to quote from the introduction of Stephen Law's "Believing Bullshit":

    "But It Fits" is a popular strategy for dealing with powerful evidence against what you believe. In fact, "But It Fits!" does a double duty. Not only is it a great immunizing strategy, it can also be used to create the illusion that a ridiculous belief system is not after all ridiculous, but at least as well confirmed as it's rivals".
    What Aaron says is broadly similar to the belief of our Dr Thomas, who himself postulated a pre-creation world, to "fit" with what was being discovered in his day. Such strategies abound amongst the religious.

    1. I agree. So long as it appears self-consistent, it might as well be true, right?

      But even fairy tales can be self-consistent.

      What matters is what the evidence shows. If there's no evidence, then there's no reason to believe.

      I'm aware of most of the various ways creationists try to make the evidence fit a pseudo-literal reading of the Bible. However, I don't think any of them come close to explaining it, for the reasons mentioned in this article.

      The Old Earth, young creation idea fails because the fossil record doesn't support it. If the rocks are old, then the fossils in the rocks are likewise old. Thus the evidence contradicts any notion that all life was a recent creation.

      The day-age idea fails because plants rely on the sun to survive. It also ignores the many symbiotic relationships between animals and plants. It also gets the order of plants and animals wrong - putting seed-bearing plants before marine life, and "all birds" before land animals. Birds are actually descended from dinosaurs, namely Theropods. Marine mammals are descended from land animals.

      The 'prior-creations' idea fails because there is no evidence of the kind of global cataclysm that would result if the world was completely destroyed and re-created. The fossil record shows gradual change over a very long period of time. If anything there is more evidence for evolution in modern animals (shared genetic errors for example), so it doesn't matter where someone tries to draw a line in the fossil record, there's still evidence for evolution since then.

      And then there's the fact that there is no evidence of a global flood any time in the last 10,000 years.

      Basically the only way to salvage creationism at this point is if someone wants to come up with a contrived scenario where God created everything as per the Bible, but then made it look exactly as if everything had evolved. Not exactly an honest assessment of the evidence, if you ask me.

  4. It is also completely untestable, and anything untestable will only ever be a claim (ref: Russell's Teapot). That's not to say it is definitely wrong, just that we will never know.

    Also, I always like to compare the idea of a (re)creation 6000 years ago with a (re)creation, say, 10 minutes ago. On the basis that the (re)creation was given false age, it is equally likely to have been 10 minutes ago based on the physical evidence we have.

    I think we need to keep in mind that physical evidence (e.g tree rings, for which we have dendrochronological records of for over 13,000 years in the northern hemisphere) is stronger than written evidence (e.g. an ancient text saying 'this tree was planted in the year 4004 BC'). It is easier for words to lie than objects, or 'actions speak louder than words' as they say.

    1. Maybe Last Thursdayism will catch on one day...

      Re your last paragraph - I think this is difficult for some Christadelphians to accept. Many of them talk about the Bible as "the word of God", as if that has been somehow verified with 100% certainty. I like to remind them that they just have a book written by people a long time ago. They may believe those people were told what to write by God, but that is yet to be determined, and in fact I think there are many good reasons to doubt that hypothesis.


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