Watering down the mislabelled “aquatic ape hypothesis”

The so-called Aquatic Ape Theory (AAT) is very well known. Ask an audience of people interested in human evolution if they’ve heard of it and practically all of them will put their hands up. If you then ask them if they think it’s a good idea, almost all of them will put their hands down again.

Now, if you ask them to tell you what it actually is… it is interesting to see how many put their hands back up again. I did this in December 2004 at the ASHB (Australasian Society for Human Biology) conference in Canberra, Australia. A few did indeed put their hands back up until I qualified the question a little by saying that I didn’t mean “what you think the hypothesis is” but “whether you could remember reading a paragraph in the literature where it was unambiguously defined”. After that, no-one had their hand up. So, basically the situation regarding the AAH appears to be something like this: It’s an idea about human evolution that everyone has heard of, that most people think is rather silly, but no-one can tell you, unequivocally and authoritatively, what it is!  Now I do not think that is a very strong basis for a refutation. Indeed, if you spend time looking through the scientific literature for that key refutation, that winning argument as to why it is wrong or a single piece of evidence which even implies it might be wrong (forget the notion of disproof in matters to do with paleoanthropology) I predict you will have a frustrating time.
There are very few pieces in the scientific literature (in English only, I’m afraid, I wouldn’t dare comment on other languages) which discuss it properly, a clear minority of which attempt some kind of rejection. The most significant, volumnous and balanced is still Roede et al 1990. It includes 22 papers, pitching 11 in favour of the AAH against another 11 critical of it, rather as if it symbolised some ‘grand final’ football match. Overall, the conclusion of the authors was against the AAH but readers should understand that, if this was a football match, it was no thrashing. A closer analogy would be more like a 1-0 win after a hotly disputed penalty decision in injury time that crept over the line after hitting the goalie and both posts.
Apart from the 11 papers in Roede et al against the AAH, I’ve only found 5 others that attempt some kind of critique, and none of them are very good. (Click here for details.)  In comparison there are over 40 pieces of literature by proponents (excluding the 11 in Roede et al 1990) and at least another 4 papers that are neutral. In science there is no concept of ‘majority rule’ or democracy but even so, with less than 30% of the entire published literature on the AAH critical of it (and most of that just uses straw man arguments) it’s difficult to see how the ‘aquasceptic’ view appears to have won primacy. One is tempted to ask: How did that happen? And on what basis were the three rejections made?
It is the purpose of this web site to suggest that this hypothesis has simply been misunderstood and as a consequence exaggerated from the start. If one forgets the images of primate seals, or mermen and women which presumably must have flashed in the minds of most critics and, instead, simply take the original proponent, Sir Alister Hardy, by his word and ask the question ‘Was Man More Aquatic in the Past?’ (with the emphasis on the word more) it is my understanding that the idea is perfectly plausible. After all we do swim better than our nearest relatives the apes. We do have some traits which are unusual in primates but quite common is some aquatic species. Apes do tend to move in shallow water in the same way we do on dry land… bipedally, a characteristic almost no other mammal shares with them.  I’ve spend much of the last ten years of my life studying this area back in academia and the more I do the more convinced I am that the idea might well be right, if only one’s impression of what it’s actually claiming is scaled back a little. Of course the evidence we have indicates that there never was an aquatic ape (in the sense that a seal is an aquatic mammal), but who really ever thought there was? I didn’t. I’ve always taken the AAH to mean that our ancestors lived next to water and, occasionally waded, swam and dived, that they were merely more aquatic than our ape cousins. People have tended to assume that only very strong selection pressure could have caused the differences between apes and humans that we see but no-one seems to have questioned whether the same profound changes might have resulted from even very slight levels of selection.
The risk of drowning (and hence the likely selection of traits to reduce that risk) is disproportionately high compared to the percentage time one needs to spend in water for it to happen. This, I think, is the key point about this idea that everyone, both sceptics and proponents, have misunderstood most.
I have become convinced that the so-called “aquatic ape hypothesis” has been unfortunately mislabelled and as a result understandably misunderstood, and then quite outrageously misrepresented. My aim in building and maintaining this web site is to try to help correct this trio. Firstly, “it” should be renamed. And, already there we come to a problem. It is not an “it”, it should be a “them”, as in the plural. One key misunderstanding of the this idea is that there is just one hypothesis when, actually, there are several. They vary in the proposed timescale for a “more aquatic” phase or phases, the specific habitat or scenario being proposed for this, the degree of selection required and the specific evidence used to support it. This makes it quite a challenge to define but, at least they are all based on selection from moving through water so, I think, it is possible to find a kind of “lowest common denominator” of them and take it from there. So, I suggest we rename them “waterside hypotheses of human evolution” (as first suggested, I think, by Philip Tobias) and then defining this umbrella label as clearly as possible. Hopefully, as a result, it will no longer be misrepresented and instead, at last, some decent science will actually be done to test it.

Waterside Hypotheses Defined
So, let’s start, at last, with a simple, testable definition of what these kinds of ideas actually are.

Waterside Hypotheses of Human Evolution:
Assert that wading, swimming and diving for food have acted as an agency of selection in the evolution of human beings more than it has in the evolution of our ape cousins both before (and hence causing) the split between these lineages and after. It notes that even very slight levels of selection can still result in profound and rapid phenotypic changes.

Algis Kuliukas
January 2015

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