Evolution, Macdonald, Nestor

Andrew Wayne Austin aaustin at SPAMutkux.utcc.utk.edu
Tue Sep 7 17:24:54 MDT 1999

On Wed, 8 Sep 1999, Philip L Ferguson wrote:

>For instance, if you look at something like dimorphism in the primate
>world: there is a substantial difference in size between male and female
>gorillas and bigger males have more chance of mating and passing on
>their genes, than scrawny male gorillas.  Among humans body size makes
>no difference at all. ... This is because our development is social, not

There is even less sexual dimorphism among the gibbon and the siamang than
among Homo sapiens (sapiens differences are around 15 percent, gibbon and
siamang differences are zero). In fact, identifying the sex of a gibbon
requires a medical exam. Neither the gibbon nor the siamang have achieved
a high level of cultural development (arguably, they have achieved none at
all). One would assume, then, that they are subject to natural selection
(at least those that live in the wild). What explains their lack of sexual
dimorphism? Obviously culture is not a necessary condition for variable
sexual dimorphism.

The decrease in sexual dimorphism is a general trend in hominid evolution.
The reasons for this are not very clear, but I don't believe the high
degree of sociocultural development achieved by Homo sapiens explains it.
For comparative purposes, culture has to be extended to other species in
the genus Homo (all of which are extinct), as well as other genuses in
Hominoidea (foremost among these is Pan, who demonstrates rudimentary
cultural achievement). On this basis, it appears that the presence of
culture is also not a sufficient condition for variable sexual dimorphism.
Indeed, among the robust clades of the Australopithecines (or
Paranthropus) there was extreme sexual dimorphism, yet these species were
far more culturally advanced than Chimpanzees.

Andy Austin

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