Re: Hominid speciation, w

Ralph L Holloway (
Wed, 2 Aug 1995 23:57:20 -0400

On Sat, 29 Jul 1995, J. Moore wrote:

> Agreed, though I'd also suggest that claiming completely effective
> reproductive isolation, with no possibility of interbreeding, also
> carries with it a burden of proof that has not been truly met, but
> is more assumed. Going into the specifics necessary to attempt to
> convince the field that this hybridization took place and was
> important enough to create the variation seen in habilis and which
> evidently led to erectus is gonna be difficult, to say the least.;-)
> But the most obvious start in naming a specific specimen is
> KNM-ER1805: relatively large cranium, sagittal and nuchal crests,
> and small teeth. That's an intriguing mix.
I sure don't disagree here. Complete reproductive isolation simply cannot
be proven from the fossil record, and I think your point about being too
rigid regarding such possibilities of interbreeding is injurious is
probably true.
KNM-ER 1805 is one such difficult specimen. It has a parasagittal
crest on one side (not really midsagittal) which some believe to be an
injury, and it does have a large nuchal crest. The mandible associared
with it appears disproportionally small, particularly with regard to the
height of the horizontal ramus, and the teeth are small. The thing that
drove me nuts was when I was trying to use discriminant analysis on the
endocasts (1978 Royal Society Conference) 1805 was continually
classified as a gorilla! Sort of embarrassing for paleoneurology....
Others thought it was the male counterpart to KNM-ER 1813, but the shape
of the endocast is quite different between the two, so the sexual
dimorphic position doesn't appear too convincing to me.

Ralph Holloway