naked bipeds

Alex Duncan (
20 Oct 1995 01:31:53 GMT

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.
>Hairy bipedalism has heat rejection problems. Naked quadrapedalism
>has heat input problems and cold night problems.
>How could these two changes happen in a "coordinated" fashion to
>result in the successful hominid package?

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). 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

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.

Australopithecines were probably not functionally hairless, because:

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

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.

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. 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. Finally, we see good evidence from
depositional contexts for hominid niche expanding to include open country
w/ H. erectus.

refs of interest:

Ruff CB & Walker A (1993) Body size and body shape. In (Walker A & Leakey
R, eds) The Nariokotome Homo erectus Skeleton, pp. 234-265. Mass: Harvard
U Press.

Ruff CB (1994) Morphological adaptation to climate in modern and fossil
hominids. Yrbk Phys Anthrop, 37:65-108.

Shipman P & Harris JM (1988) Habitat preference and paleoecology of
Australopithecus boisei in eastern Africa. In (Grine FE, ed) Evolutionary
History of the "Robust" Australopithecines, pp. 343-380. New York: Aldine
de Gruyter.

-- this last also discusses habitat prefs in early Homo.

Alex Duncan
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086