Re: naked bipeds

Thomas Clarke (
20 Oct 1995 14:38:50 GMT

In article <466u69$> Alex Duncan <> writes:
>In article <45sdmd$> Tom Clarke,
> writes:

>>The problem is to get from hairy quadrapedalism to naked bipelism.
>>The route for the change must be positively adaptive at every step.

>You betray some misunderstandings about evolution when you say the route
>for the change must be "positively adaptive at every step". A more
>realisitic statement would be that the route for the change must not be
>maladaptive at any step (or at least not too maladaptive).

Yeah, I was being sloppy. Its that pesky open interval versus
closed interval thing in math, do you include the case A=B
along with the cases A>B?
I don't think your clarification changes substantially what I
was trying to say, though.

> There is
>every reason to think that a great deal of what happens in evolution is
>random, and happens when newly evolved features are not selected for or

I guess I am very much a follower of Dawkins and those who use
the concept of a phylogenetic landscape. By "adaptive", I, of course,
mean reproductively fit. Thus while variations are random, only
those that lead to increased reproduction (adaption) increase in
frequency so that the population tends to evolve in the direction of
those traits.

>As far as naked bipedalism goes: you seem fixated on the idea that
>functional hairlessness and bipedalism must have evolved at the same
>time. This is not a fixation shared by paleoanthropologists.

Yeah, I was thinking about this.
I think I have been so persuaded by all the arguments about the
thermoregulatory advantages of nakedness for a biped on the
savannah, that I came to the conclusion that to be successful
in the savannah or mosaic environment, the biped should be naked.

>Australopithecines were probably not functionally hairless, because:

>1) They were small enough that they didn't have severe heat retention

Has anyone done the calculations relative to this like have
been done for larger hominids?
(The Ruff reference?)

>2) They probably weren't hanging out in the "savanna." Most of the
>information available indicates that australopiths were occupying (one
>more time for the hard of hearing) MOSAIC environments. They probably
>stayed in the shade as often as not.

Do any of the references support this directly?
If the mosaic were such a fine grained mosaic that you could
scurry back to the shade from the meadow and stay out of
the noon-day sun, then would there have been much selection
pressure for the development of bidedalism? I would think
that chimps could venture out into a forest meadow and then
back to the protection of the forest using their current mode
of locomotion.
Thus, I would think that the hominds spent substantial time
out on the savannah exercising their bipedal skills
(Else where is the selective advantage of bipedalism?
Or lack of disadvantage)

>Postcranial anatomy that we would associate with diurnal open country
>foraging first appears w/ H. erectus (maybe w/ H. rudolfensis, but the
>material is scrappy). H. erectus were also substantially larger than
>australopiths, and would have had more problems w/ heat retention.

I look at pictures of Lucy's bones and the bones of the Lake Turkana
boy and, except for size, they don't seem all that different, post

The surface area body volume relation cuts two ways. Not only is
it easier to reject heat with a small body, but the insolation per
unit mass is larger for a smaller body.

> Based
>on the evidence at hand, it seems most likely that functional
>hairlessness (along w/ heavy sweating) first appeared w/ H. erectus and
>not w/ the australopiths.

Could be. No direct evidence either way.

Stupid editor ate it, but you said something that H.e times
were also associated with expansion into open habitats.

Here I point out that there were other factors, the open
habitat was expanding due to climate changes and also tool
use indicates behavior changes. Shelter building makes extended
stays in the open possible?

Thanks for the references.

Tom Clarke