We don’t mean why are we going bald. We mean why aren’t we covered with hair, like any respectable mammal. We split with the chimps 7 million year ago, and before that, the gorillas. They have plenty of hair. What happened to ours?Monkey

Because of the lack of hair, we have had to evolve pigment, invent clothing, and a lot of other hassles. Once we lost it, for whatever reason, wouldn’t it have been simpler to simply evolve it back. (Maybe the Europeans are part way there. They are ahead of the Africans and Asians in this category.)

Chimps have no pigment. Check out this bald one. Quite a rosy complexion. No need for pigment apparently if you have hair. (Look at the muscles on that guy. No wonder chimps can brachiate. Wouldn’t that be fun?)

Two sorts of mammals tend not to have hair. Wallowers like the hippo, rhino, pig, and elephant have little, although the latter two do, or at least did, come in hairy versions. Secondly, we have the aquatic mammals, whales, dolphins, walruses, and manatees.

This has led to a charming theory that hasn’t the least shred of fossil evidence, called the Aquatic Ape Hypothesis. According to this, we were forced at some point into some sort of semi aquatic lifestyle, and underwent a series of adaptations. The theory keeps popping up every couple of decades in one form or another. The theory is entirely circumstantial. Its main elements are:

  • We are hairless, like dolphins, whales, and walruses.
  • We have big brains, like dolphins and whales.
  • Baby fat. We produce these plump buoyant progeny whereas the other great ape offspring are notably scrawny.
  • All the other primates are knuckle walkers. They can walk upright, but choose not to. However, knuckle walking is not such a good idea if wading in relatively deep water.
  • Hold your breath. We have voluntary control over our breathing, a handy trick if you plan to spend much time under water. For other primates, this is apparently involuntary. (How they know this is also a mystery.)
  • Humans love to bath and swim. It’s ‘natural’. Our great ape friends can swim, but won’t unless forced to.

The list continues, but we won’t.ape theory

Are you convinced? Probably not, seems quite a stretch, plus if we could evolve all that aquatic equipment, why didn’t we un-evolve it once we were back on terra firma.

Still, the hairlessness is a pretty good puzzle. Maybe some day some fossils with flippers will turn up. Of course doing an evolutionary stint in the sea is rather a romantic notion, so maybe that is what propels the Aquatic Ape Hypothesis.

But aquatic existence isn’t the only possible explanation for hair loss. Perhaps at some point in the past, we were wallowers. Now admittedly that has a lot less charm than the aquatic theory but could we amass some evidence for the Wallowing Ape Hypothesis. Lets give it a shot.pig

  • Hair: We’ve got little, just like the hippo, pig and elephant.
  • Brains: Elephants have very big brains. Pigs too. Wallowers must need big brains.
  • Fat: Pigs, elephants, rhinos, and hippos are not exactly what you would call svelte.
  • Bipedalism: This could come in handy if you wallowed into some mud pit that was unexpectedly deep.
  • Hold your breath. Don’t try any serious wallowing without this feature.
  • Swimming: Is there really any difference between wallowing and swimming? Isn’t it just a question of the density of the chosen liquid. Perhaps bathing represents our subconscious wallowing tendencies.

Please do feel encouraged to extol your own theories of our strange hairlessness in the comments section. There must be lots of other possibilities. Please note that all comments will be taken just as seriously as you took this post.

  4 comments for “Hairlessness

  1. January 18, 2015 at 6:57 am

    Human fur loss is no puzzle. All fossil, paleo-environmental, physiological show that human ancestors during the Ice Ages (Pleistocene Homo) did not run over open plains (sweating water + salt, both scarce in savannas…) as often assumed in popular & sopetimes in less popular views on human evolution, but followed the African & Eurasian coasts & rivers (e.g. 1.8 mill.yrs ago at least as far as Java, Georgia, Algeria & Turkana), beach-combing, diving & wading bipedally for littoral, shallow aquatic & waterside foods (recent info e.g. google researchGate marcverhaegen). No need for far-fetched “explanations”, simply compare with other tropical (semi)aquatic mammals. No wonder we lost our fur: we take our clothes off when we go for swim. And no wonder we didn’t regrow & fur: we now use clothes outside the water.

  2. January 20, 2015 at 10:41 am

    Marc, yours is a fun take on the issue. I doubt there is a linear logic to the problem but if so yours is a valid contender. Dr. Mike

  3. Ken F
    February 5, 2015 at 9:08 pm

    I still think there’s something to be said for an ectoparasite hypothesis – disease can be one of the most potent drivers of evolution, changing the makeup of a population within a few generations.

    My own thinking is that this would not be simply because parasite would be more easily seen – which, of course they are, especially on children, where the ‘furlessness’ trait is most strongly and universally expressed – but because they work as ‘feelers’ that are exceptionally sensitive to the presense of bugs.

    Our body hair (all hair) extends our sense of touch beyond the skin. It is our first line of defense (detection) against biting bugs and my own are so sensitive the air vibrations from passing insects are easily felt. It takes conscious effort to NOT brush, swat or otherwise react (“Get it OFF, Get it OFF!”) to the sensations caused when a bug encounters those hairs. And, all else equal, by being smaller, hairs are more easily displaced or vibrated and should detect smaller bugs more easily than heavy, large hairs; “All else” being how well endowed with nerves the follicles are. According to Montagna “Evolution of Human Skin” (1985), all human hair follicles are very rich in nerves, irrespective of size and comprise the largest component of skin sensibility. He likens the nerve supply of ‘ordinary’ hairs/follicles of humans to the exceptionally nerve rich follicles of dedicated feeler hairs in related apes.

    This doesn’t preclude other advantages to retaining the “furless” trait, including that of better hot weather endurance, but it seems to offer an immediate benefit that (unless the sweat glands were already in place) heat dissipation would not.

  4. February 7, 2015 at 10:43 am

    Oblique, but fun: in humans there is a tendency to the hairier, the more alcohol dehydrogenase and the better alcohol tolerance an individual has.

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