Re: Hominid speciation, was h

Alex Duncan (
24 Jul 1995 16:25:14 GMT

In article <3urv0m$> KathieDon, writes:
> I think that hybridization is a reasonable way of resolving the "H.
>habilis" question. Of course we can't know what the genetic distances
>were like, but I think it reasonable to suppose that they were small
>enough that fertile cross-breeds between, say, robust australopithecines
>and whatever 1470 was.
> The picture, then, is something like this: at about 2 million years
>ago, we don't have clearly defined species, but rather a continuous gene
>pool with strongly developed clines--the equivalent of "racial" variation.
> Out of this pool we eventually get H. erectus and a robust species.
>These last two apparently didn't interbreed because we don't have (at
>least I don't think we have) intermediate morpholgies, not after about 1.7
> Could this be right? And if so, is the "pool" continuous with the
>ancestral ramidus-like populations? That would mean that from about 4
>and a half million years ago, to about 1.7 million years ago, we had
>diversification at the morphological (and presumably behavioral) level
>with little or not diversification at the genetic level. An interesting
>set of affairs.

First off, there are problems with this because there is good evidence
that Homo and Australopithecus were separate genera as far back as 2.5
Myr, and perhaps much further given the morphology of WT 17000 (the black

Hybridization is not really a reasonable suggestion for the morphology
that we see in ER 1470, especially as we don't have a really good idea
what the precursors to this individual were like. Robust masticatory
anatomy was almost certainly plesiomophic for hominids, and thus
shouldn't be too surprising in earliest Homo.

Modern models for hybridization don't support the idea that the 2 Myr old
hominids formed a single continuous gene pool. The Papio "superspecies"
is the best thing we have going for a primate model, and this consists of
a sequence of "species" that are skeletally almost indistinguishable. A
more reasonable explanation for the diversity of hominid morphologies
present at 2 Myr is that there was an adaptive radiation that took
advantage of uniquely hominid positional behaviors.

I can not accept the idea that specimens as diverse morphologically as OH
24 and OH 5 belonged to the same gene pool.

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