Jim Moore's "AAT Sink or Swim?" Web Site
AAT Claims and Facts: Hair and Hairlessness
Moore's attempt to blow the AAH argument that our greater
hairlessness was the result of an adaptation to swimming speed out of the
water fails because of several misunderstandings (at best).
1) This is not the whole argument, just a part of it.
Moore implies that the whole AAH case is based on the assumption that it
improves swimming speed, when it is not. Sweat cooling also clearly benefits
from nakedness but could not have evolved as an thermoregulatory mechanism
unless generation after generation of our ancestors had an extremely
reliable source of water. The simplest scenario is that it evolved as an
adjunct to 'going for a dip' in hominids living by the water's edge. Moore
completely ignores this argument. Even the swimming argument itself is based
on more than speed. It also includes better durability and energy
2) Moore claims that as hairiness in humans varies and
has clearly changed greatly since the last common ancestor, this negates the
aquatic argument. But this ignores the possibility that the first humans to
emerge from Africa might have been the most naked. (Certainly the hairier
groups of modern humans appear to be Indo-Europeans that must have become
exposed to harsher climates quite soon after the African exodus.) It also
assumes that the AAH argument proposes a distinct aquatic phase millions of
years ago. Although this is what Hardy and Morgan originally proposed, it is
not the view of all proponents of the AAH.
Note the point in that sentence there... "relative to apes". This is a very important point but unfortunately it is a point Moore completely ignores for the rest of the page.
He then claims that this idea has two fundamental flaws. The first one is that humans actually have quite a lot of body hair and that it has clearly varied greatly in recent human evolution and therefore any proposed 'phase' millions of years ago is unlikely to account for it. The second is that many aquatic mammals are also hairy.
These points are both correct, of course but Moore is conveniently forgetting the important part - "relative to apes" and, once again, exaggerating the AAH argument to an unsustainable point by over-emphasising comparisons with true aquatics and pretending that it is the only factor that the AAH is proposing.
Taking his first point first: Even the hairiest Caucasian 'he-man' is relatively naked compared to a typical chimpanzee. There is clearly a wide variation in human hairiness, indicating that it can change relatively quickly, but if you look at the majority of human groups the 'norm' appears to be closer to the completely naked range and hairier people would appear to be the exception, perhaps in peoples that have moved away from tropical to temperate zones. It seems most likely that the original African ancestor of all humans today was, relatively hairless.
point is often wheeled out in this argument. Of course many aquatics and
semi-aquatics are hairy. Aquatic factors are clearly not the only ones which
affect the level of hair cover in mammalian species. One also has to
consider body size, the amount of time it spends out of the water and the
likely air temperature when it is outside of the water. For true aquatics
like cetaceans and sirenians, they are committed to a life permanently in
the water and so have evolved very thick sub-cetaceous layers of fat to
completely replace any need for body hair as a thermoregulatory device.
Because they never leave the water body hair has been completely
An analysis of the instances of hair loss in Mammalia shows that it has probably evolved on at least eleven separate occasions:
1) Cetacea (Whales, dolphins)
2) Sirenia (Dugongs, manatees)
3) Odobenus (Walruses)
7) Some Xenarthra (Armadillos)
8) Pholidota (Pangolins)
9) Heterocephalus (Naked Mole Rat)
10) Some Suidae (Babirusa)
11) Homo sapiens
It is clear, looking at that list that the hair loss has usually been the result of either some aquatic factor, large body size or a burrowing lifestyle or some combination of them all.
As it is rather unlikely that body size (on the level of an elephant or rhino) or burrowing underground could be seriously considered as factors in our evolution, that leaves the effect of water as the most plausible. And this is the conclusion one would reach even before considering whether other members of that list (elephants, pigs and perhaps even rhinoceroses) also had a similar 'more aquatic' phase in their past. Moore deals with the aquatic rhinos idea in a separate, new, page in his web site and I'll critique that page separately too, alongside the comparable arguments for the elephants and pigs.
If we add to this the rather unambiguous evidence that Moore himself provides - the Sharp & Costill (1989) paper showing that shaving body hair in male competitive swimmers reduces drag and, as a consequence, improves swimming performance - we can see that the hair-loss for aquatic reasons argument has, at least, some basis in fact..
If this was the only factor in our make up that indicated that moving through water may have acted on our phenotype one could understand the scepticism but, of course, it isn't the only one. It is merely just one of a cluster of traits which all seem to point the same way.
Moore then goes to some trouble to find references which suggest that seal skin is nothing like human skin and that cetaceans slough off skin nine times faster than humans do.
Well of course they are different. Humans are not evolved from seals or dolphins. This is a classic piece of misunderstanding of the AAH argument. It assumes that if the AAH argues by analogy, then those arguments can be refuted by showing that the analogy is limited and that other aspects of the same animal claimed to be analogous are contradictory. The extreme case would be to argue that as dolphins have lost their limbs, the AAH needs to explain why humans do not also have reduced limbs. It is arguing from the ad absurdum position and always completely forgets the simple phylogenetic fact that humans are primates and that therefore, every analogy has to be placed into a cladistic context.
Humans, remember, are less hairy than apes, our closest relatives in the animal world. We have to consider why that might be. Desmond Morris described the situation beautifully in his 1967 book 'The Naked Ape':
"Staring at this strange specimen [Homo sapiens, the naked ape] and puzzling over the significance of its unique features, the zoologist now has to start making comparisons. Where else is nudity at a premium? The other primates are no help, so it means looking further a field. A rapid survey of the whole range of the living mammals soon proves that they are remarkably attached to their protective, furry covering, and that very few of the 4,237 species in existence have seen fit to abandon it."
We end up looking back at that list of eleven again. And, if you're objective, you have to consider that, compared to chimps and gorillas we are more aquatic than they are but not really larger and certainly not more prone to burrowing under ground. So why is this idea treated with such derision?
and convergent evolution
Assuming humans all had little or no body hair, like some aquatic mammals, Moore asks the very pertinent question: "what about that necessary feature of evolutionary convergence, similarity in function?"
He claims that AAH proponents are coy in answering this but, when they do, they "can come up with only one reason: to swim faster". After which Moore, happily sets about the task of destroying this argument with simple arithmetic arguments about the speed of sharks and crocodiles versus the speed of the fastest competitive swimmers and the 3-4% improvement that shaving body hair might just give them according to Sharp & Costil (1989).
Once again, Moore has demonstrated the aquasceptic method beautifully. Take one part of one argument in isolation and pound it to death. Hold up what remains and declare victory.
First of all where has any AAH proponent ever claimed that swimming pressures exclusively led to human nakedness to the exclusion of any other factor? If we take just one alternative causal factor - aiding sweat cooling - one can see, rather quickly, that this must have also been a big part of it. Humans do sweat copious amounts in certain situations and most evidence would indicate that losing body hair would make the resulting convective heat loss more efficient.
If one thinks about this a little bit longer then it is also clear that such a evolutionary response to overheating could not have evolved far from very reliable sources of fresh water. Therefore sweat cooling as a cause for nakedness, like the swimming argument, has most explanatory power when it is considered in a water-side habitat.
Moore doesn't mention the sweat cooling argument on this page because anyone with an ounce of common sense would agree that it makes most sense as an adjunct for going for a dip to keep cool. Instead he hides the parts of the argument that contain basic common sense and extracts the bits which, if placed in the right context, can be made to just look daft.
Take next, his further contention that AAH proponents only consider nakedness helped so our ancestors could "swim faster". Note, not more efficiently, or with more durability - just faster. Why did he do that? Presumably that he can run that argument against sharks and crocodiles.
I don' think I need to cite any references to back my claim that not everyone who has died in water has been the victim of a crocodile or a shark. People drown and our ancestors have almost certainly always drowned. The argument the AAH makes is simply that our ancestors were more exposed to this danger of drowning than were the ancestors of our ape cousins. If naked skin can give a 3-4% reduction in drag in water then, clearly, this is going to be a factor that would be strongly selected for in situations where groups of hominids were at risk of
drowning. Floods and tides are just two situations where this trait would benefit and therefore be likely to be selected for.
Next, Moore accuses 'someone' - he doesn't say who - of using his work to argue against the hypothesis.
He writes "One AAT proponent has taken my points above as evidence for an aquatic background. His mistakes in doing so are instructive."
He then accuses this mystery person of continuing the "long-standing AAT tradition of dishonestly reporting only part of the evidence I found; the part about the study that points to hair removal as possibly producing a slight benefit in speed. But he ignored the other two items of evidence I also found, both of which suggest the opposite effect".
He added "Second, he made an error in reasoning by asserting this speed increase would help individual, less-hairy hominids because they would swim faster and be at the front of a fleeing pack of which the rearmost individuals would be most at risk."
I wonder who the mystery person could be. Well, I think it might just have been me, actually. See this link ('Jim Moore's own goal') to a posting I put up onto the newsgroup about it.
Putting aside the slur of dishonesty (how dishonest is it to make an accusation and not even name the person you're accusing) I have to retort that I didn't mention the Sokolov data because it was to do with seals and, you know, the argument is only an analogy.
The argument about speed swim suits being ridged is interesting enough and if I missed it it was in error. But the fact is that these suits are not hairy. Perhaps if humans had been even more aquatic we might have further evolved more ridged naked skin.
about crocodiles being stealth hunters and that sharks are many times faster
than humans are valid enough. The answer to them is two-fold:
He says "we know that not all humans have extremely long head hair, even when it is allowed to grow without being cut, and not all humans have little or no body hair. Yet both these characteristics are said to be explained by an aquatic period in our ancient past, long before the species Homo sapiens sapiens arose."
Part of this, presumably, is based on Morgan's argument that women's scalp hair may be longer than males (and apes') because as an adaptation for allowing infants "fingers to twine into" (Morgan 1972:p36). Clearly some women do have shorter hair which might argue against that factor but, in any case, it is not a major part of the AAH argument.
Moore ends this page by listing the big problem (although he lists it as three points) with the nakedness for swimming argument: That because there is great variation in the hairiness of members of Homo sapiens and because we know that this variation has occurred since the last common ancestor, "the AAT explanation that it happened millions of years before that must be incorrect."
the logic here. (Must it be incorrect on this basis? I don't think so) Moore
does make one valid point: the original view of the AAH was that our
ancestors when through a distinct and relatively long 'phase' when all of
these changes happenned. The idea was that this phase occurred since the
last common ancestor with the apes but before the speciation event of
Sharp, Rick L; Costill, David L (1989). Influence of body hair removal on physiological responses during breastroke swimming. Medicine and Science in Sports and Exercise Vol:21 Pages:576-580