The Aquatic Ape Theory is being discussed over at Pharyngula. As PZ points out, an excellent resource on this idea is Moore’s site on the topic. Here, I just want to make a few remarks about it.
The Aquatic Ape Theory (AAT) is a human evolution Theory of Everything (TOE) and thus explains, as it should, everything. That is a dangerous way for a theory to act, because if it tries to explain everything then it is going to be wrong in a number of places, and it is going to seem (or even be) right in a number of places but only by chance. (Unless, of course, the TOE is totally rad and really does explain everything.)
For these reasons, a human evolution TOE will generally evolve into a zombie that won’t die and can’t be killed, potentially eating the brains of science geeks and graduate students for decades. Another example of a human evolution TOE is bipedalism. Here, the idea is that bipedalism explains everything. For a long time that TOE ate the brains of graduate students and the general public and even senior scientists. It no longer does for this reason: We now know that bipedalism evolved millions of years before many of the key human traits that we wish to explain. But the zombie is not completely dead. Many human evolutionists still make the claim that bipedalism was a very important step in human evolution, even though a) we can’t explain why it happened and b) there is no solid link between bipedalism and anything else. The fact that we are increasingly realizing that bipedalism evolved in many hominoid lineages may make this TOE go away eventually. So, for now, the Bipedalism Zombie doe not consume brains wholesale. It just scoops out a tablespoon here and a tablespoon there now and then.
The AAT is different from the Bipedalism TOE for a couple of reasons. For one, it was rejected a long time ago by almost all serious paleoanthropologists. It is quite possible that the fact that the theory was being promoted (but not originally generated) by a Welsh non-academic female and that she was being aggressive about it probably influenced more scientists (negatively) than many aspects of the theory. That would be unfair, and it probably was unfair. But after a while, the AAT began to demonstrate other reasons for its rejection.
The AAT, in its various forms over time, has addressed almost every general aspect of human anatomy and behavior and made the claim that an aquatic ancestry is the best explanation for that feature. Some of these claims were absurd. For instance, the “fact” that females have long hair was an adaptation to living in the water, where the long flowing locks of females would be used as life lines for her babies and toddlers (‘paddlers’?) floating around her.
One of the best possible forms of evidence for an aquatic phase would be to find other mammals that are not presently especially aquatic (or at least no more than humans), look for physical evidence of that adaptation, and then check for that evidence, surviving as physiological atavisms, in humans. Not finding such atavisms is meaningless, but finding them would be spectacular evidence.
For example, elephants may have gone through an aquatic stage, and this is in fact seen ontogenetically in their kidneys. Do human kidneys also show this kind of evidence? Well, no, sorry, they don’t. The fact that elephants would have gone through their aquatic phase much longer ago than humans does not help the AAT here.
When the AAT was first proposed, we had a murky view of human evolutionary history. At that time it was possible to suggest a single phase of evolution during which certain conditions prevailed, and from which a long list of human traits emerged. But since that time our understanding of human evolution has become more detailed and many of the human traits are now seen as having emerged at very different times over a multi-million year period of time. For the AAT to continue to explain all of these traits (hairlessness, bipedalism, large brain, head hair, body fat distributions, body size, leg length and form, atavistic webbed feet, seafaring, intense use of coastal resources such as shellfish, etc. etc.) it would have to be the case that our ancestors were ‘aquatic’ for millions of years.
For the entire time that the AAT has been extant, the theory itself has been rather murky. Just how aquatic? Were the babies born under water or on land? Was mating done under water? Was aquatic lifestyle facultative or did all hominids do this? All day every day? Was all the food aquatic? On top of this, only a few of the usual candidates for typical mammalian aquatic adaptations are seen in humans. Hairlessness and subcutaneous body fat were, of course, considered early on to be hallmarks of the aquatic adaptation. The fact that aquatic mammals do not vary in hairlessness (very much) and humans do is a problem. The fact that body fat distributions are sexually dimorphic seems to have been missed by the AAT. Or maybe not. Maybe there is a version where the females are aquatic and the males are not. They meet on the beach for romance. Thus, the link our species makes, psychologically, between beaches and romance!!! Aha!!! It explains everything!!!!!
Oh, sorry, … I’ve got control now, didn’t mean to go off like that…
So, you can see where the theory goes, and how in fact it can’t be stopped. The AAT is a zombie theory, untestable because so much of what it proposes has not been framed in a testable way. The AAT remains capable of consuming many more, still untapped “connections” and “explanations.” The AAT has consumed many brains, and not all of them particularly susceptible. Just recently, I heard from an excellent, unimpeachable source that a very famous person whom you have heard of is an AAT ‘believer.’ I found it hard to believe, but it is apparently true. Some day I hope to have a little conversation with this person!
AAT: The theory that keeps giving. And eating brains.
UPDATE: See this video just in.