isolation/speciation etc

Alex Duncan (
13 Nov 1995 13:07:28 GMT

In article <> Paul Crowley, writes:

>There are two sorts of evolutionary change and this error confuses
>them: (a) where the species gets split by a geographical feature or
>environmental change and gradually drifts apart, as we see with
>chimps, gorillas and orangs within the last 2Myr; and (b) where a
>small group establishes a new ecological niche, for which it will
>need a relatively short period of isolation.
>I think that we are agreed that hominid speciation resulted from
>the second mechanism. Do you also agree that climatic change
>(especially an adverse one) is unlikely to have been a factor?

So, you're saying that geographical separation and habitat changes
couldn't have happened at the same time? Most indicators for the
relevant time period indicate that paleoenviromental changes resulted in
1) new habitats, and 2) probable isolation of populations of a once
geographically continuous species.

>BTW I keep seeing the "evolution forces" error everywhere, and it
>drives me bananas. Today's UK Times has a report from Dr Charles
>Goodhart of Cambridge Univ stating the some h.s.s. were "forced"
>by climatic change to move south around 70kya. (It's only a news-
>paper report so I may be being unfair to him - but it is typical.)
>My point is that such change is slow in terms of a hominid lifetime.
>No h.s.s. packed his bags and said "Brrr, it's getting cold, let's
>go to Egypt this winter". It's a tempting scene, but it could not
>be more wrong.

I think you read things into what you see that aren't really there. As
far as modern H. sapiens moving South during glacial maxima: there is
circumstantial evidence that it really did happen. This is currently one
of the better explanations going for the temporal overlap of Neandertals
and moderns in the Middle East. No one is suggesting that one day a
modern checked his weather charts and decided his niche had moved. Nor
is anyone suggesting the move happened within a single generation. What
is being suggested is that during glacial maxima, the niche moderns were
comfortable with gradually moved south, and the moderns went with it.

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