Convincing evidence for human evolution

November 2, 2023 • 11:30 am

I occasionally get questions like this one: “What do you consider the most convincing evidence for evolution?”  My answer is usually “the fossil record combined with dating methods,” but I often add that “the evidence from biogeography is so convincing that I’ve never seen a creationist even try to rebut it.” (You can see some of the biogeographic evidence in chapter 4 of Why Evolution is True, and I give the fossil evidence in Chapter 2.)

And if someone asks me, “What’s the most convincing evidence for human evolution?”, I’d also give the first answer above. That’s because the temporally ordered record of human evolution shows a fairly clear progression from the morphology of an ape somewhat like a chimp (i.e., our common ancestor with the chimp and bonobo that lived about 6.4 million years ago).  It’s not a straight line pathway, and we don’t know all the details, for human evolution, like all evolution, is a branching bush, and some branches went extinct.

When I was on a BBC Three show, “Conspiracy Road Trip,” with each of us assigned to convince a group of British creationists of the truth of one bit of evolution (mine was to dispel Noah’s Ark and the great flood scenario), the most convincing evidence to the creationists was the presentation of an evolutionary series of hominin skulls by Tim at White at Berkeley. That bit begins at 42:26 in the video below (I appear earlier).

This week I got a note from an upset parent whose child attended a religious school where the kid was told that humans could not possibly have descended from apes. I responded that humans were apes, and we descended from a common ancestor with chimps (and from other ancestors with other primates)—an ancestor that, I suspect, looked rather chimplike. (It is of course a misconception that we descended from living chimps.)

I tried to help the parent by giving him evidence for human evolution, and that included this photo from the Smithsonian, posted on Talk Origins, Doug Theobald’s site), showing (with the exception of the skull at the top left corner), various hominin skulls laid out in temporal order.  

The key:

Figure 1.4.4. Fossil hominid skulls. Some of the figures have been modified for ease of comparison (only left-right mirroring or removal of a jawbone). (Images © 2000 Smithsonian Institution.)

Note that the skull at upper left is the skull of a modern chimp, so it doesn’t really belong with the others. It’s just there for comparison. But look how things change over time: the face gets pulled back, the teeth get smaller, the brow ridges shrink, and most evident, the braincase gets larger.

Creationists have big trouble with this because they don’t know where to draw the line between “apes” and “humans”. Some maintain that every fossil earlier than some arbitrary one (say a Homo habilis) is an “ape”, while everything after that is simply a human (they might even say “a malformed human”!) But that tactic is so arbitrary and capricious that it’s not convincing even to some of the British creationists above.

I like the photo simply because it’s a wonderful piece of evidence for human evolution, with the skulls laid out in temporal order. (Now they’ve eliminated the “robust” hominins, and that would confuse things a bit though it would be more accurate, for the robust hominins are still hominins. It also leaves out more recently discovered fossils such as Homo floresiensis, the tiny “hobbit” hominin that went extinct about 50,000 years ago.

Also, we don’t know that this is the line of evolution to modern humans (and it probably isn’t), but it does show gradual change over time that’s undoubtedly genetic, and that is what evolution means.  We do not see fossils resembling modern humans 3 million years ago, but we see them now. The earliest hominin skulls we see resemble the skulls of early apes, and gradually evolve into skulls that look like those those of modern humans.  What better evidence of human evolution could we wish for? I’m always amazed that fossils really exist, and also that human fossils are especially rare—yet there are enough of them to provide convincing evidence that our species evolved from a common ancestor with other apes.

Putting the chimp skull in the figure does cause some confusion, as described at  by Kambiz Kamrani:

I have some slight problems with this image, though. The biggest problem, and a common misconception I see in regards to understanding human evolution, is the whole we descended from chimpanzees train of thought. This image compounds it. The lineage of primates that have become the chimpanzees have been evolving independently of the human lineage. And because the non-human primate fossil record is rather spotty — it is hard to see these types of trends and transitions that we see in the above image happen along in chimpanzees.

Working on that note, this composition implies that our ancestral form was a chimp and once the chimp and human lines diverged then humans went through many natural selection events while chimps just remained stagnant as chimps. That’s wrong. Chimps and humans share a common ape ancestor.

But if you point out that the modern chimp skull is simply there for comparison, and that in all likelihood is fairly similar to the skull of our common ancestor with modern chimps, the problem disappears. Still, many people think that we evolved from modern chimps, and it takes some doing to dispel that idea by explaining the branching pattern of evolution and the idea of common ancestry. Those are a bit harder.

32 thoughts on “Convincing evidence for human evolution

  1. IMO the best evidence for human evolution by far is the DNA evidence. Shared ERVs, shared DNA breaks/repairs, shared pseudogenes and shared segmental duplications. This all is explained beautifully in Graeme Finlay’s book on human evolution. I’ve never seen solid evidence for evolution like this and the creationists have no rational answer. Also, he’s a Christian so that’s a plus – a cancer researcher. The easiest to understand and perhaps most elegant is the shared DNA repairs and unique patches. Ya hoo! Best evolution evidence, human evolution, and “macroevolution” evidence I’ve seen in 50 years in the creationist trenches.

    “DNA breaks are random and potentially catastrophic. The molecular details… are yielding to stringent molecular analysis, which have revealed that the telltale messiness of the repair patch is inherent to the repair system. Random breaks are fixed by the desperate co-option of any available DNA… Such patches are sufficient evidence of great ape monophylicity.” ~ Graeme Finlay.

    1. Yes, I should have added, “Evidence that can convince people very quickly.” The DNA evidence is very convincing, but it takes some time to explain to people, and most people don’t know what DNA is (take my word for it, I used to have to explain forensic genetics to juries!) The fossil evidence is grasped rapidly, like by those creationists. Just explaining the DNA evidence would take a lot of time and turn off some people. But you do make a very good point!

    2. That’s my pick. The human genome project (and of so many other species including primates) completely changed the game. It has even corrected and refined the paths and timing of hominid migrations out of Africa and across the globe. It has corrected errors in morphology.

  2. I had not noticed the Chimp skull in the classical figure, which I’ve used in class. But it was possibly put together many years ago. A fair substitute now would be a skull of Ardipithecus, which would be quite similar to the Chimp and a reasonable proxy for our more ape-like ancestor.

    1. A fair substitute now would be a skull of Ardipithecus

      Or “Toumaï” (Sahelanthropus tchadensis).
      The problem is that we don’t have any fossils of the forest-dwelling apes of the mid-late Miocene. And given the typically low pH of tropical forest soils, we’ll be lucky to find such. The fossil record (to date – there’s always a “to date” in palaeontology) starts as [whatever the forest-dwelling apes were] came out of the forests into drier savannah-like environments.
      The search isn’t hopeless (that was one of the reasons for the searches in Chad which yielded “Toumaï” ; and why they’ll be resumed when the security position improves), but to date it has been unsuccessful.
      Going further back into the history of the apes, there are the abundant remains of Proconsul in East Africa (but that’s from 17~21 Myr ago (inconveniently older than Australopithecus at 2~3 Myr) and the much more fragmentary remains of Afropithecus, which is barely younger (16~18 Myr) and … well, fragmentary. But between them and “Toumaï” or sediba, there is an inconvenient gap.
      Which is why people are still looking. Non-creationist people.

      1. The problem is that we don’t have any fossils of the forest-dwelling apes of the mid-late Miocene.

        If there are no fossils, how do we know they existed?

        I know that sounds like a creationist “gotcha” question, but I’m actually interested in the real answer.

        1. Several reasons:
          – A weak reason: The forest biotope is popular among chimps and bonobos.
          – A stronger reason: Both the four extant chimp subspecies and the bonobo species are found in the forest biotope, suggesting some or most of their evolution happened there.
          – A popular reason: The forest biotope would explain the spotty fossil record, as other comments say.

  3. Agree that the above image starting with the modern chimp adds to the problem. Maybe this would be a better visual: 2 rows of photos, each starting with the SAME ‘common ancestor’ skull, as far back as we can. Then every X years, show the changes in parallel, one becoming a modern chimp, and one morphing into modern humans. But keep those 2 rows separate as best as possible, and for Bio 101 simplicity, keep all the branching out of it. I could draw it better than explain it, I think.

    1. That is a great idea, but as far as I know (and I’d be delighted to be corrected), we just don’t have a sequence of chimp-descent fossils that is anywhere nearly as detailed as what we’ve got for hominids (and even that is not comprehensive).

      1. I don’t think we’ve got any fossils that are definitely chimp-not-human ancestors. Not one. I’d be delighted to hear of one. Between Proconsul (link above) and “historical” chimpanzees, nothing. Except possibly the fragmentary Arfopithecus (link also above – why hasn’t the post come up yet? Is the current site code objecting to more than a couple of links in a post? )

      1. Exactly right! I looked into this some time ago. The hot, wet conditions in a rainforest do not provide an easy environment for fossilisation. I seem to remember that someone found a hominid tooth, or teeth, from the chimpanzee line, some years ago now, but as far as I know that’s all we’ve got.

  4. I know nothing about this, but I’m slightly surprised that K and L are categorised as the same sub-species; they look distinctly different to me.

    (Jerry, the Smithsonian links in the “key” give “page not found” errors.)

    1. That’s the classical “long” skull shape versus the “short” shape. And yes, it has been the source of much spilled ink.
      On the other hand, the skulls are nominally 15 kyr apart. 500+ generations. Look at two other skeletons separated by that number of generations and at least one glacial advance, with a high likelihood of population bottle necks, effectively random extinction of lineages and a good chance of random drift becoming fixed.
      “brachycephalic” is one shape, but I’ve forgotten the other. Others : “In anthropology, human populations have been characterized as either dolichocephalic (long-headed), mesocephalic (moderate-headed), or brachycephalic (short-headed).” ( I haven’t descended into the Slough of Phrenology, but I’d be surprised if they didn’t have a long and involved typology of head shapes, but the Neanderthal (and Cro-Magnon) brachy/dolchi discussion was a real thing and probably reflects real population differences. Whether there was any adaptive significance is another question.

  5. Thanks, Jerry. I’ll use this in my ongoing crusade (If I can still use that word) against Facebook creationists, and you are right to point out the difficulty of including chimpanzees in the sequence although I completely understand why it was done – I’ll make that clear. The only problem in my mind with this page is the use of the term “macro-evolution”. I really wish scientists wouldn’t use “macro” and “micro” evolution, it’s a gift to the ID variety of creationists who use it to try and say that micro-evolution is explicable (house cats and lions are related) while large scale macro-evolution (trees and people can’t be related). There is only one evolution, but try telling them that.

  6. I was never in the creationist camp, but for much-younger me, skeletal homology really drove the reality home. It made me wonder how anyone would not be convinced of common ancestry between humans and AT LEAST other vertebrates. I specifically remember two events—first, seeing the giant turtle fossil skeleton at the Yale Peabody Museum (Google: Yale Archelon) and marveling at its similarity to my own skeleton; and second, looking at a bat wing skeleton, with its tiny arm and hand so much like mine.

    1. Many good examples of just that. Compare elbows between a human skeleton and a cat or dog skeleton. The human elbow has various features like the trochlea, capitulum, olecranon fossa, etc etc. etc (an elbow is a complicated hinge joint). Then look at the elbow from the cat or dog, and immediately see that they have the same structures!

    2. When I was five, my creationist mother showed me a cabinet full of hominid skulls, arranged to illustrate a family tree, in a science museum. To her credit, she did not censor the exhibit. But her insistence that evolution was simply “false” and “long discredited” was so unsatisfying that I still remember this incident. Once I could read, I thought, I would figure out the truth.

  7. Creationists do indeed fret about the line between apes and humans. I wonder how they would react if we informed them that there is no line: Humans *are* apes. We are apes with important new characteristics, but we are part of the clade that includes all apes.

    I agree that the most convincing evidence for most lay people is the march of skulls through time, showing the numerous transitional forms. Genetic, morphological, developmental, behavioral, biogeographic and other factors are also definitive—particularly when taken together—but these are all a bit more abstract than the paleontological evidence from skulls. The skulls are so in your face that they can’t be denied.

    1. “Darwinian man, though well-behaved,
      Is at best a monkey shaved.”-W.S. Gilbert

      The idea that humans are apes is a major reason that creationists reject evolution. I don’t think that their objections are really based on, say, the second law of thermodynamics, even if that’s what they say.

    2. The skulls are so in your face that they can’t be denied.

      As a hyper-social species, we are highly face-oriented. We’re good at remembering them (“Hi, George Weasley!”) differentiating between them (“oh, sorry Fred.”), describing them to others (every novel with a description of the chief protagonist before page 2). A large part of our social institutions are based on identifying people by their faces, and not being fooled. “In your face” is indeed why they’re powerful evidence needing very little interpretation.
      In contrast to, say, AGTCAAGCTAGCTTAG [3000 pages deleted for brevity].

  8. It would be interesting to know if any of them have changed their position in the eleven years since that was filmed.

    1. That is a very good question.
      I’d be unsurprised if the original road trippers refused to take part though, if there were a “12 years on” version. (In another window, trying to find contact information for the production people.) Those who hadn’t recanted their religious position are likely to feel attacked for holding that position. Those who have recanted their position may well have lost friends/ family/ social standing for recanting. Either way, not wanting to bring the subject up again is a high-likelihood outcome.
      Ah, the series was “Conspiracy Road Trip”, with episodes on UFO believers, Creationism believers, and 7/7 bombing (dis-?) believers. Programme website ; no name of an external production company.
      Half an hour searching later – still no name for the producer. The embedded video link is telling me that “Warner Bros Intl has blocked the video from [my] country on copyright grounds.” Trying the link directly … and it’s also blocked that way.
      Does anyone have a VPN to outside the UK, who can tell us the producer’s name? Most likely they’re no longer at Auntie Beeb (if they ever were), but they should know who still has access to the production materials, including necessary contacts if someone was interested to make a “12 years on” update of the series. I think that the idea is at least worth putting to Auntie Beeb.
      What are Warner Bros doing with (some) copyright on a Beeb programme?

  9. Or, as Delaware Senate candidate and creationist, Christine O’Donnell, famously said on the Bill Maher show back in the day, confident that her rhetorical question would befuddle her opponents: “Why aren’t monkeys still evolving into humans?” In a way, she was right. It was befuddling. Where do you start in responding to something that many layers of stupid.

  10. I only recently learned of an interesting connection between humans and monkeys and apes— That we share the same basic blood types. The ABO blood groups that are found in humans are also found in monkeys and apes. They’re not identical, of course, as would be expected with several million years of separation between our species. But they are fundamentally very similar.
    Chimpanzees seem to be mostly Type A, for instance, while Orangutans have all four blood types that are found in humans.
    This is powerful evidence for a common ancestor between humans and other primates, in my opinion.
    There have been numerous studies of blood types of different animals, and blood types seem to be species specific. A cat has three blood types and dogs have 13. And they are not compatable. But Lions and Tigers have the same three blood types found in domestic cats and dogs have very similar blood types to wolves. So it seems that only members within the same basic species will share blood types.
    So I wonder how creationists would spin this?

  11. Like the erroneous classical “descent” image that implies modern chimps at the root, I would like to see a rearrangement.

    Put modern chimps and modern humans alongside each other and – if we have no fossil closer to the common ancestor – the first hominin at the root.

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