Re: Why is Homo sapiens hairless?

John Waters (
4 Nov 1996 01:39:02 GMT

T&B Schmal <> wrote in article
> I don't know the answer for hairlessness but here is a
possibly different
> approach. Look at the environment of the new biped -
what are the other
> animals in it wearing? The lions, the zebras, the
baboons. Hair. Why?
> Follow with me on this. Why don't these animals just
wear skin and forget
> the hair. What is it that hair has that gives them the
survival edge? If
> we can answer that question, then maybe it will be
evident why man does
> not need all that much hair.
> So what are the plusses of hair?

JW: In the case of Lions and Zebras the hair is very short
and has little thermoregulation value. Its main purpose
seems to be related to camouflage. Lion infants are
spotted, to enable them to merge in with the bush country
where they are born. Zebras are striped to create confusion
in the minds of potential predators.

Generally, hair is adopted by specie which need a variable
insulator. Extra hair can be grown in winter, then moulted
in the summer. In marine species of mammals, such as seals
and whales, there is a contant temperature differential
between that of the marine environment and the mammalian
core body temperature. So a fixed insulator like blubber is
perfectly appropriate. Seal infants are born on the land,
where there is a large differential between day and night
temperatures, so they have a thick coat of fur.

The whole business of insulation has to be related to an
animal's environment and its surface to mass ratio. In
addition, there are factors like an animal's metabolic rate
to consider. Species which use up a lot of energy very
quickly produce far more heat than relatively somnolent

Human females have a fixed layer of subcutanous fat
concentrated in certain parts of their body. This is a
permanent form of insulation which means they require less
body hair than primates without such layers of fat.

If clothes were used as a means of camouflage, and the
maintenance of the camouflage was essential for survival,
then there would be an advantage accruing to hominid
individuals with less hair, or more sweat glands etc.

However, this form of evolutionary selection would only
occur if the hominid thermoregulatory mechanisms were
insufficient to combat overheating problems. This could
well be the case in daytime savannah conditions in Africa.

That said, if the hominid thermoregulatory mechanisms were
insufficient for hominids using clothing, the same would be
true for hominid females carrying their babies in their
arms. The latter event would lead to both increased
subcutanous fat in the nursing female, and a general
reduction in hair growth of the infant. This would seem to
be a more parsimonious hypothesis explaining the reduced
hairyness of hominids, than the adoption of clothes.