Re: Hominid speciation, was h

Gerold Firl (geroldf@sdd.hp.com)
28 Jul 1995 13:04:53 -0700

In article <3uvbc6$lk1$1@mhade.production.compuserve.com> Mark Fagan <71640.2463@CompuServe.COM> writes:

>I could never buy into the idea that there was SO MUCH gene flow
>going on between, China, southern Africa and northern Europe (as
>they are today), so that one single species evolved concurrently
>throughout the old world.
>
>I see no reason, though, that anatomically modern people spreading
>out from Africa could not have interbred with local populations of
>earlier hominids and so aquired some of the local characteristics.
>Especially if they were adaptive.

The alternatives you propose are complementary rather than exclusive. If
modern h. sapiens originated in africa, spread throughout the old world,
and interbred with the local humans, thus explaining the continuity of
regional anatomical markers such as the shovel-incisors, then by definition
sufficient gene flow to maintain a single species among all hominids was
occurring.

The most realistic model of human evolution and speciation must include
local evolutionary divergance, diffusive gene flow, and large-scale
migration. Attempts to simplify the model by insisting on exclusive "out of
africa" or "candelabra" processes do make it easier to conceptualize our
history, but ultimately obscures the dynamics of actual evolution. Whenever
local adaptation/mutation/invention resulted in a selective advantage with
respect to neighboring groups, a genetic overflow would spill-out; if it
was large enough, then groups would actually migrate out of their
homelands. A smaller advantage would radiate using a diffusion process.
Some adaptations were more global than others; the neanderthal
cold-adaptations, for example, could never flow back into africa (though
they got pretty close - neanderthal remains have been found in palestine, I
believe). Intelligence, on the other hand, is advantageous no matter where
it originates, and hence knows no geographical or climatic barriers.

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