Does Lucy Prove Evolution?
Last year was the fiftieth anniversary of the discovery of the Lucy skeleton, and Paul Garner and I recorded a two-part episode of Let's Talk Creation discussing the skeleton and its interpretation (part 1 and part 2). In the second part, I tried to address the question of whether the Lucy skeleton constituted good evidence for human evolution, and even while I explained it to Paul, I thought, "This is not clear. I'm going to get flak for this." And sure enough, there were a few comments on the YouTube video that basically said my response was rubbish. Fair enough. Let's see if I can clarify my thoughts.
My intention with that section of the video was first to notice that it's a massively loaded question. As a scientist, I think about evidence and models in ways that aren't like the average person. An average person hears "X is good evidence for a theory" as "X proves that theory is true." Evidence, in common conception, is decisive. If a theory is true, it has good evidence. If it's false, there's no evidence at all.
When I hear "X is good evidence for a theory," my first reaction is, "We'll see about that." I understand that most models have lots of different sorts of evidence, and one piece of evidence is rarely decisive. It can happen, of course, but the more common way a model is accepted is by the accumulation of many different types of evidence explained by that model. It also helps if a model can explain things that the competing model does not explain or explains poorly.
Because of these different perceptions of "evidence," When people ask me if Lucy is good evidence for evolution, it's just a massively loaded question. If I simply say yes, the average person will understand that to mean that I think evolution is true or that human evolution a proven fact. In the video I was trying to make the point that evolution is a more complicated concept than that. Origin of Species did not provide some decisive new evidence in favor of evolution. Origin wove together a body of existing evidence with a series of novel observations that in the minds of many convinced them that evolution must be true. The transition from geocentrism to heliocentrism also came from a whole range of evidences no one of which was decisive. Galileo's observations were only peripherally related to the structure of the solar system, which is why his advocacy of heliocentrism was not decisive.
In that regard then, my point in the video stands: The only reason people think Lucy is "good evidence for evolution" is because we have lots of other reasons ("other evidence") to think evolution is true. Is that a point in favor of evolution? Sure, but is Lucy any more important than Neandertals or Homo erectus or Ardipithecus or Oreopithecus? She's one piece of a much bigger picture. For me, the only thing that makes Lucy (and the rest of the hominins) remarkable is the very vague implication of evolutionary theory that something like Lucy must have existed. If humans gradually evolved from nonhuman primates, then something with a mix of human and nonhuman traits must have existed at some point in the past. Notice there's no guarantee in evolutionary theory that we'd ever find fossils of such creatures. Nor is there any specificity about what sorts of traits these "intermediates" might have. Which came first, walking on two legs, big brains, or manual dexterity? There's nothing in evolutionary theory that would specify in what order those traits must have evolved (if they did evolve). There's also nothing in evolutionary theory that would specify where these creatures lived. We think Africa largely because that's where fossils of the right sort of anatomy and age have been found. One might argue that the presence of extant chimps and gorillas on the African continent indicates that Africa is our ancestral home, but that's based on evidence rather than strictly on the model. The assertion that "humans evolved like everything else on this planet" does not tell you where they evolved, how they evolved, or what their evolutionary predecessors looked like, except in the very vaguest sense.
Now I don't want to downplay the importance of predicting intermediate forms. That is definitely something that evolution generally suggests must be true, and it's not something that the creation model of the late nineteenth century anticipated. So credit where credit is due, but the idea that Lucy enjoys some kind of unique evidentiary importance in the argument for human evolution is just a fallacy. Finding Lucy did not prove human evolution which otherwise would be in serious doubt, and critiquing the Lucy skeleton does not damage human evolutionary theory to any great extent. She's not a lynchpin.
I'd say there are three-ish things (depending on how you count them) that make Lucy's species important beyond the vague "intermediacy" of her anatomy. First, she's positioned at an important radiometric age, 3-4 Ma, where we don't know about many other taxa. Now you might say, what about anamensis, and that leads me to my second point: Her species Australopithecus afarensis is known from many different fossils. Au afarensis is probably the second best known hominin after Neandertals. So yes, there are other taxa known from the 3-4 Ma period, but they are not as well known as Lucy and her kin. (Thus, you might say that these two reasons constitute just one: Au afarensis is the best-known species from that time period.) The third reason that Lucy is important is a mashup of the timing and publicity of her discovery. There were many fewer hominins known at the time she was found. There was much less exploration of that part of Ethiopia at the time of her discovery. Johanson made a big deal out of her discovery. In retrospect though, we can see now that that one skeleton is just a piece of a much larger body of evidence.
So does Lucy prove evolution? No, I don't think any rational person can say the Lucy skeleton is any sort of decisive proof of evolution. If she had never been discovered, there would be no massive crisis of confidence regarding evolution. The more important question in my mind is how well hominins in general and Lucy more specifically can be explained in alternative models, such as the one I outlined in the video. If you don't want to rewatch that episode, here's a little written summary:
- My baraminology studies have always separated humans and Au. afarensis in different created kinds. Hence, Lucy's species is an animal not human.
- Because Lucy was found in the remains of very localized, ancient lake deposits along with stone tools made from local volcanic rock, the skeleton appears to be the remains of a post-Flood creature that descended from ancestors that survived the Flood aboard the ark.
- Consequently, Lucy is part of the diversification of ape species after the Flood. Her death and preservational circumstances testify to a period of post-Flood residual catastrophism that is conceptually part of the creation model, established from other sorts of evidences. Hence, Lucy is in a small way a confirmation of predictions of the creation model.
But can we explain her mix of "human" and "nonhuman" characteristics? Well, first I'd say those are loaded terms. They're only "human" and "nonhuman" characteristics because now we see them segregated in that way. In the past, there have been much more diverse humans with a variety of traits we do not see in modern humans, and there have been much more diverse apes with locomotory adaptations that are not found in modern apes. So we need to be careful about how we understand these characteristics. If we could see the full diversity of humans and apes as God made them and before extinction wiped them out, Lucy might not be such a big deal after all.
That said, I do not think evolution has any sort of monopoly on the explanation of intermediate forms, mostly because there used to be an explanation for such forms. Throughout the Middle Ages and beyond, people conceived of life as arranged on a Great Chain of Being. The chain was imagined to run from inanimate matter through fungi and plants to animals to humans to angels all the way up to God. The Chain is why we originally had conceptions of "lower" or "higher" animals before evolution was ever seriously considered. Had Lucy been discovered in the 1600s, she might have been explained like this:
I shall therefore now conclude this Discourse, with a brief Recapitulation of the Instances I have given, wherein [Lucy], more resembled the Humanekind, than Apes and Monkeys do: As likewise sum up those, wherein it differ'd from a Man, and imitated the Ape-kind. The Catalogues of both are so large, that they sufficiently evince, that [Lucy] is no Man, nor yet the Common Ape; but a sort of Animal between both; and tho' a Biped, yet of the Quadrumanus-kind.
Thus in the Ape and Monkey-kind, Aristotle’s Cebus I look upon to be a degree above his Cynocephalus; and his Pithecus or Ape above his Cebus, and our [Lucy] a higher degree above any of them, we yet know, and more resembling a Man: But at the same time I take [her] to be wholly a Brute, tho’ in the formation of the Body , and in the Sensitive or Brutal Soul, it may be, more resembling a Man, than any other Animal; so that in this Chain of the Creation, as an intermediate Link between an Ape and a Man, I would place our [Lucy].
And if you think I'm daft, you should know that I adapted that description from Edward Tyson's description of the anatomy of the first chimpanzee known to western science, published originally in 1699. (The above passages are taken from pp. 91 and 5 in the 1699 edition found at Archive.org, as indicated below.) He made quite an emphasis on the intermediacy of the chimpanzee between humans and other animals, all while affirming that the chimp was an animal of the ape kind and evidence of the Great Chain of Being.
Now of course the Great Chain has long since been abandoned as too simplistic, but it still stands as one of the only conceptions of classification that predicted organismal form in the same way evolution does. Thus I conclude it is not necessary to conclude evolution is proved from intermediacy alone. There could be other explanations.
As a result of all of this, I feel very comfortable saying that the final chapter in Lucy's story has yet to be written. She's important, no doubt. But important for what exactly only time will tell.
Check out Tyson's book on the chimpanzee:
Feedback? Email me at toddcharleswood [at] gmail [dot] com. If you enjoyed this article, please consider a contribution to Core Academy of Science. Thank you.
Have you read my book? You should check that out too!
