Re: Hominid speciation, w

J. Moore (
Sat, 29 Jul 95 11:07:00 -0500

Rl> I always thought that there was a sort of "mini-adaptive radiation"
Rl> that took place around 2 MYA, but I never thought it might be related to
Rl> hybridization. I forget where I alluded to it, but my view was that that
Rl> stone tools, meat-eating (at least in so far as tools would be found
Rl> associated with faunal remains), tool-making and slaughtering sites, all
Rl> pointed to a sort of "revolution" (far too strong a term) of
Rl> symbollocally-mediated social behavior that would have enlarged adaptive
Rl> niches for exploitation. I can believe that hybridization could have
Rl> played a significant role in hominid evolution, but we are up against
Rl> the old lurking beast again, as represented in the biological species
Rl> concept and the morphological criteria sufficient to apply that concept
Rl> to paleontological evidence.

That's a big problem, and probably one without definitive answers.
Massive numbers of fossils would help, but when you look at the
numbers of specimens people try to have available when they're doing
taxonomic analyses of, say, modern birds, we're talking
thousands of specimens (whole specimens, not just bones), and
that's gonna be a long time coming. So definitively recognising a
biological species from fossils is, I would think, always going to
be problematic (just have to try our best).

Rl> burdun of proof however, must fall heavily on someone suggesting that
Rl> australopith A is a hybrid 'tween robust and gracile australopiths B and
Rl> C, or ditto for early or later forms of Homo.

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.

Rl> Taxonomy is not one of my strong suites, and I've always viewed it
Rl> as a an intellectual convenience to have labels at the species level, if
Rl> for other reason than it helps students memorize the material!
Rl> (Students, hell, I need those labels myself!) I think hybridization will
Rl> work well for the Middle East and East European Neandertals, but beyond
Rl> that, I am skeptical.
Rl> Ralph Holloway.

Of course a lot of people don't go for the idea of hybridization
at all, even at the level of Neandertals. I think the labels are
great, whether they are "species", "sub-species", or just
whatever, as something showing similarities and differences.
It would be awfully confusing without some sort of grouping (I
find it quite confusing enough even with the groups).

The problem arises when these labels are assumed to necessarily
accurately describe the actual reproductive potential of the
individuals so labelled. When that is done, and it's done a lot,
it closes down a potentially productive avenue of thought, and
then the labels become problems rather than solutions.

Jim Moore (

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