Re: Why Large Gap Between Species...?

Rohinton Collins (
9 Dec 1996 19:06:58 GMT

Paul said:

> The principal restraint on dimorphism in chimps is probably
> their partial aboreality -- while there are advantages in
> extra size for male chimps, the disadvantages of extra size
> and weight in the trees are manifest. If chimps were to
> adapt to a 100% terrestrial existence, then substantial extra
> dimorphism would almost certainly result. This is probably
> close to what actually happened about 4.6 mya.

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?