Re: Why Large Gap Between Species...?

Laurie Davison (
10 Dec 1996 13:32:02 GMT

"Rohinton Collins" <> wrote:
>What about the orang-utan? It is almost totally arboreal, but the male is
>twice the size of the female. Your argument of an increase in sexual
>dimorphism in body size (SDIBS) being curtailed by arboreality is simply
>not borne out by the evidence. The extant apes show a very good correlation
>between SDIBS and social organisation. Why do you insist on pitting
>yourself against the entire palaeoanthropological community Paul?

Actually, the male orangutans remain primarily on the ground and the
females in the trees. I'm not sure what selection pressures led to this
separation of the sexes, but the male's large size restricts his ability
to be arboreal. The males and females rarely come into contact with one
another unless mating. Also - the males are known to kill off the young
in this species as well - perhaps that's the selection pressure right
there, eh?
I'm not taking sides here - just putting in my $0.02...