Hair and "Hairlessness"

One of the AAT/H's principle claims to fame is that it explains the human hair pattern and amount of hair relative to apes; it's generally at or near the top of their list of "aquatic traits". The AAT/H claims that humans lost their body hair as a result of an aquatic or semi-aquatic phase in our past, claiming this is an aquatic adaptation. There are two fundamental flaws in this reasoning:
  1. From the fact that many humans today have a lot of body hair, we can safely surmise that this feature varied during the time span of our species, Homo sapiens sapiens, instead of changing -- as the AAT/H typically requires -- during the transition from the LCA to hominid (LCA = last common ancestor between apes and hominids).
  2. A great many, probably most, types of aquatic mammals are hairy, so we see that losing body hair is not an aquatic feature.

There's more on that second point on a later page which lists all the aquatic and semiaquatic mammals and how many times aquaticism and semiaquaticism has evolved in extant mammalian lineages. Not only are the majority of aquatic and semiaquatic mammals hairy, you should look at how often aquaticism or semiaquaticism arose in extant mammals -- how many distinct lines lead to an aquatic and semiaquatic mammal species today. For instance, beavers evolved their semiaquaticism separately from otters, but all pinnipeds (seals and walrus) today descend from a common aquatic ancestor. When you examine how many distinct times aquaticism and semiaquaticism arose in mammals which are around today, you find that it's 31 times, and that of that 31 times, only 3 times did it lead to hairless mammals. The vast majority of times it led to still-hairy mammals.

What's more, of those aquatic mammals which don't have body hair; almost all are very large mammals, just like the land mammals which have little body hair. The reason large mammals tend to not have body hair is that they overheat if they have it (large shapes have a ratio of less surface area to volume than small shapes, so they lose heat slower -- this is basic physics and has been shown to be the case for animals). Also, all of those aquatic mammals which don't have body hair are fully aquatic mammals incapable of living long out of water, and they've been fully aquatic for many tens of millions of years, far longer than hominids of any kind have existed. Contrary to what you'd expect from the AAT/H claim, there are no hairless aquatic and semiaquatic mammal except for those which are fully aquatic and have been for tens of millions of years, or are either very large and almost certainly hairless due to the physics of thermoregulation, or they are both very large and fully aquatic for tens of millions of years.

None. Not one.

[Note: At this spot on this page I previously made the incorrect statement here that phocid seals (also called eared seals or true seals) don't have body hair. That is not so; they are well-covered with stiff hair.] Seal skin is also very different from human skin in important ways that indicate we didn't have an aquatic background. The outer layer of seal skin is composed of "flattened, solid, keratinized cells" (King 1983:143, Seals of the World; British Museum (Natural History), Oxford University Press). "This may be contrasted with such a layer in man for example, where enzymatic digestion of the non-keratinous parts of the outer cells of the stratum corneum results in these cells becoming mere flakes continuously shed. Such a condition in a seal could lead to the skin becoming waterlogged" (King 1983:143, ibid.). The skin of cetaceans sloughs off at an incredibly fast rate compared to humans (every 2 hours for a dolphin compared to about 18 hours for humans) and is also waterproof.

Clearly human skin is very unlike that of hairless aquatic mammals. Unlike the skin of these aquatic mammals, human skin quickly becomes waterlogged (this is why your fingertips wrinkle when you're in water), an obviously undesirable trait for a purportedly aquatic animal.

Body hair and convergent evolution

The aquatic ape theory uses the evolutionary concept of convergence to explain why aquatic mammals have little or no body hair.  Ignore for a moment the undeniable fact that aquatic mammals don't always (in fact, don't usually) have little or no body hair, and look at the principle of convergence as it relates to this loss of body hair. How does hair or the lack thereof fit into the principle of convergence? Does the AAT/H explain this feature?

Assume for a moment that humans today are pretty much the same in terms of having little or no body hair -- okay, I know it isn't true, you know it isn't true, anyone who takes a moment to think or who has ever seen Robin Williams take his shirt off in a movie knows it isn't true, but for a moment, pretend it is true. Then we have several groups of mammals which have little or no body hair: extremely large mammals, extremely fast-swimming mammals with specialized skin, naked mole rats, some pigs, and humans. The group of extremely large mammals include elephants, hippos and rhinos, as well as whales, manatees and dugongs. Walruses, Northern sea lions (Steller sea lion), and elephant seals are often said to be in this group, but they do have hair over almost all of their bodies. The group of extremely fast-swimming mammals with specialized skin includes porpoises and orcas, and some of those aforementioned whales. Humans quite obviously don't fit into any of these categories, so right away we can see that the AAT/H seems doomed to fail to explain this supposed hairlessness of humans by claiming it's a convergent aquatic evolutionary trait. The question that AAT/H proponents typically fail to ask is: what about that necessary feature of evolutionary convergence, similarity in function?

Mostly AAT/H proponents are coy on this point, declining to point to any such similarity, as if mere contact with water. even just wading, is enough to create this change. Those that are more honest in their theorizing can come up with only one reason: to swim faster. Looking at the list above, we can see that it seems to be the only possible reason. But is it a sensible reason? Would selection pressure have worked its magic on this feature to make us faster swimmers during an aquatic phase?

Catching fast food and escaping aquatic predators would seem like a good idea to say the least, but would losing our body hair have done it? There are two parts to this, does it make us faster? and is "fast" fast? Second question first: human swimmers are, sadly, pathetically slow. The fastest human swimmers in the fastest Olympic event can't quite manage 6 miles per hour, and they're one heck of a lot faster than average people (twice as fast or faster). Given the long legs which propel them, we can be pretty sure that they're one heck of a lot faster than our early ancestors too. Yet 6 miles per hour is slow; it's a speed which can be easily exceeded on land by children (that fat kid down the block can do better than 6 mph). It's also deadly slow in the water, crocs and sharks are several times faster. A shark wouldn't even have to kick into high gear to catch an Olympic swimmer (assuming the swimmer saw the shark coming, which is a whole other ball of wax -- see the section on predators).

Now for the first question, does lack of body hair make us faster swimmers? Sure, we already know it can't make us fast enough, but does it make us faster at all? Since we've seen swimmers shave their body hair for years now, it might surprise you as it did me to find that there was no real attempt to experiment and see if it actually worked until fairly recently.

When I looked this up some time back, in literature on sports physiology, I found one study which showed an effect that could possibly help swimming speed, although actually helping swimming speed was not demonstrated. ("Influence of body hair removal on physiological responses during breaststroke swimming", Rick L. Sharp and David L. Costill, Medicine and Science in Sports and Exercise 1989: 21(5), pp. 576-580.) That study showed a difference in build-up of lactic acid in the muscles in athletes who had shaved their bodies, a slight increase in distance per swim stroke, and an "insignificant decline" in heart rate, which all together indicated reduced effort in swimming. This, it was assumed, would lead to an increase in swimming speed. They also showed a slight increase in coasting distance (compared to a control group) when a swimmer dove into a pool when that swimmer had shaved their body hair. These differences, they felt, could be as high as 3-4%, which would work out -- for the fastest Olympic swimmers in the fastest event -- to as much as one-quarter of a mile per hour. This would be important for competition swimmers, where an increase in a quarter mile per hour might easily mean the difference between defeat and victory against other human swimmers, but against swimmers -- like crocs and sharks -- that still swim 2-5 times faster, it would have a negligible effect.

A later study, by Krüger, Mikoleit, and Heck, showed a definite difference in swimming speeds before and after a full body shaving, but ironically does not support the idea that reducing body hair appreciably affects swimming speed in humans. This study was done with both males and females, and the study notes that while "results show that body shaving leads to a clear gain in performance. It can not be explained by the reduction of water resistance by the loss of hair, as the nearly body-hairless girls show the identical effect as the boys with clearly more body hair". The males actually averaged 1/4 of 1% more improvement, and the overall improvement hovered around 2.5%; this suggests that only 1/4 of 1% of the improvement was due to hair causing drag while the other 2 and 1/4% improvement was something else -- the test demonstrated a difference in lactic acid buildup in the muscles. The main result shown in this study -- the difference in lactic acid buildup in the muscles -- is the same difference shown in the first part of the Sharp and Costill study. Lactic acid building up as your muscles work is a good thing -- up to a point. It acts as an energy source for those muscles, but if too much builds up the muscles' ability to maintain a high workload decreases. This is why the reduction of lactic acid buildup is important for athletes like these swimmers studied. So it may be that for whatever reason, shaving off all body hair, rather than simply having less body hair to start with, reduces lactic acid buildup. It may also be that shaving off all body hair leads to an improved feel for the water allowing the athlete to use better technique, which is supported by some studies but not by the Sharp and Costill study. Krüger mention that studies have shown that this effect from shaving off all body hair only works if it's done just 2 or 3 times per year; more and the effect is decreased. So whatever the reason this wouldn't help explain why hominids at some point started having less body hair, and it would only help them in water if they were shaving their body hair, all of it. That's certainly not any AAT/H scenario I've ever heard of.

The other experiment I know of related to hair and swimming speed showed a decrease in drag in seals when hair is present. In the book Mammal Skin (1982) Sokolov describes experiments which showed this effect: "Experiments on models covered with the skins of Phoca vitulina and Pusa sibirica show a reduction in drag as compared with rough, bare skin. Hence the damping role of pinniped pelage during swimming (Mordvinov and Kurbatov, 1972). A hydrodynamic tube experiment with a dummy having a Baikal sealskin pasted over it reveals that hair is conducive to an increase in the boundary layer thickness, to a reduction of the speed pulsation level within 1 to 10 khz, and to a reduction in drag." (Sokolov 1982: 60; Mammal Skin by V.E. Sokolov, University of California Press: Berkeley).

So is smooth better? The jury is still out. The past few years many more competition swimmers have been wearing body suits, but some say new records are not due to the suits. And if the newfound speed is due to these suits? The characteristics of these suits make them additional arguments against the AAT/H position on hairlessness, since they are ridged fabrics. The idea behind the suits is to recreate the same effect as seen in that experiment with that hairy sealskin and the skin of dolphins, which is covered with very small ridges. Of course the AAT/H wants it both ways; smooth bodies and hairy heads. At any rate, the speed isn't nearly enough; sharks and crocs would literally have an Olympic swimmer for lunch in a contest of swimming speed.

Let me make this point about the slowness of human swimming speeds very clear; here are the swimming world records as of July 2009.

Note: the long course is 50 meters and the short course is 25 meters so there are twice as many turns and pushoffs in the short course; the short course records are faster than the long course due to the pushoff being faster than any swimming stroke. Since we are examining swimming speed rather than pushoff I'm using the records for the long course for all distances.

Men's 50 meters freestyle26 Apr 20095.32951289 mph; 8.59598854 kph
Men's 100 meters freestyle13 Aug 20084.74388948 mph; 7.65143464 kph
Men's 200 meters freestyle12 Aug 20084.33566434 mph; 6.99300699 kph

Women's 50 meters freestyle19 Apr 20094.65776294 mph; 7.51252087 kph
Women's 100 meters freestyle27 June 20094.24657534 mph; 6.84931507 kph

Historically (early events were generally 100 meters and longer):

Men's 100 meters freestyle03 Dec 19053.39209726 mph; 5.47112462 kph
Men's 200 meters freestyle18 Aug 19023.00403769 mph; 4.84522207 kph
Women's 100 meters freestyle18 Oct 19082.34947368 mph; 3.78947368 kph
Women's 100 meters freestyle10 June 19122.76923077 mph; 4.46650124 kph

Mind you, there are good reasons to believe these speeds are faster, probably much faster, than our earlier ancestors could manage; here's a few of those reasons:

  1. these are highly trained swimmers, the best in the world
  2. these are Homo sapiens, who have long arms and legs for powerful swimming strokes, compared to australopithecines
  3. these swimmers are using a swimming stroke almost certainly unlike what would be used by our ancestors, who probably used a dogpaddle just as other primates do and for that matter just as most mammals do if they aren't specialised for swimming
But as you can see, even these elite athletes are very slow. Even in the fastest event in modern times the fastest men in the world can go slightly more than 5 mph, for less than half a minute (when I was in my 20s I could walk that fast for 4 hours or more at a time). The fastest women in the fastest event are not even up to 5 mph. When you look at the 100 meters, where the effect of the pushoff is lessened and swimming speed becomes more of the total, even the fastest men in the world can't manage 5 mph. And that's now; look at the older records: the men barely over 3 mph and the women not even getting to 3 mph; that's an average walking speed.

Even if you could make these speeds 10% faster, it would be so slow compared to potential predators that the predators would have no problem catching any swimmer they wished to. But the facts don't show a possible 10% gain in speed, at most they show 3-4% if you remove all hair, which didn't happen with humans. Couple that with the fact that aquatic predators are rarely seen before they attack and the notion that we could escape them by swimming a half mile an hour (or less) faster is just silly.

One AAT/H proponent, Algis Kuliukas, has taken my points above as evidence for an aquatic background. His mistakes in doing so are instructive.

First, he continued a long-standing AAT/H 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. While the research I found showed conflicting, and therefore, inconclusive, data, he turned that into non-conflicting and conclusive data (and another AAT/H "false fact") by dishonestly reporting only that part of the data he'd seen which supported his position (and since he read it here in the above paragraphs, we can be sure he was dishonest in his omissions).

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. There are several problems with this assumption. One is that what he describes is seen only in animals which form extremely large herds or schools (unlike any ape/hominid groups) and/or which are not incredibly slow compared to their potential predators (unlike us versus crocs or sharks). Another is that, as my section on aquatic predators explains in detail, these aquatic predators are rarely seen until they have already struck -- in the vast majority of cases, fleeing never comes into the picture.

Perhaps most instructive is what his reaction says about an all too typical AAT/H proponent's attitude toward data. I reported all the data I found on hair and swimming speed, both suggesting that hair helped and that suggesting no hair helped, and I did this because that's the way you do science -- it's the only honest and sensible way to do it -- but he assumed that I did so "by mistake" . That he would assume so tells us a lot, I'm afraid, about his own attitudes toward data, and what it tells us is not good, and certainly not reassuring vis a vis the reliability of AAT/H proponents' research.

He's also invented another piece of data which he's been using a lot online by taking one small bit of data out of one of the studies I mention above. I describe this on the page about him.


If we look around us, 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. Here again is the problem with that view:
  1. We know that humans today are one single species.
  2. We know that humans today vary in body hairiness, and in length of head hair.
  3. We know that these characteristics vary regionally.
Consequently, we know that this variation post-dates the transition to our species, so we know this sort of variation can and did arise within a few tens of thousands of years.

Therefore, since we see that either of these characteristics can come and/or go that quickly (a few 10s of thousands of years or less), any theory claiming it happened during the transition from common ancestor to hominid can only be an unwarranted assumption. Yet this is what the AAT/H states, and this unwarranted assumption is what AAT/H proponents consider a key piece of evidence for their view.

The change from the ancestral characteristics of body and head hair -- whatever those characteristics might have been -- may have happened first during the timespan of Homo sapiens sapiens, or it is possible that it changed and rechanged many times before that. But we do know that it can, and did, change quickly, and that it has changed during the timespan of our species.

So besides the intractable problem that changes in body hair would be insignificant in terms of swimming speed, the speculation in the AAT/H about how these hair characteristics changed has three basic problems:

  1. In both cases, the AAT/H speculates a change into a characteristic which is not a characteristic of our species, just of some members of our species; and
  2. since we know these characteristics changed during the span of our species, the AAT/H explanation that it happened millions of years before that must be incorrect; unless
  3. it's treated as a sort of nonsense speculation, like speculating that we may have had stripes for a few million years but they disappeared without a trace.