Re: Brain size, IQ

Gerold Firl (geroldf@sdd.hp.com)
10 Sep 1996 19:48:59 GMT

In article <rfoyDxBGqB.GBr@netcom.com>, rfoy@netcom.com (Richard Foy) writes:

|> In article <50nadd$l8c@news.sdd.hp.com>,
|> Gerold Firl <geroldf@sdd.hp.com> wrote:

|> >I have tried to estimate human genetic diffusion time, using very
|> >crude assumptions and modelling, and I get very short periods of time;
|> >something on the order of 10,000 years for genes to diffuse from one
|> >end of the old world ecumene to the other (say, zimbabwe to java).

|> Could you please post the assumptions and model you used? Did you do
|> any work to establish the senstivity of your resuls to variations if
|> the different assumptions?

Heh - when I say very crude, I mean so crude that no perturbation
analysis is necessary. I assumed that human generation times were
around 20 years, and that the average birthplace separation between
mates was 20 miles. With a hunter-gatherer small-band population
densities and exogamy, this seems reasonable.

That then implies that genes will diffuse throughout connected
breeding populations at a rate of about one mile per year. During
interglacials the sahara becomes a desert, and may well have acted as
a true genetic barrier (or at least as a serious restiction) for h.
erectus, but there does not appear to be ant indication that the
widely scattered erectus sub-populations scattered throughout the old
world diverged sufficiently to form new species.

I'm not sure how many cycles of glaciation took place during the out-
of-africa tenure of h. erectus; I would guess something between 5 and
10. During those successive cycles of isolation and re-connection new
mutations and adaptations were developing in the various erectus sub-
populations, but the species did not branch. Even if no large-scale
migrations took place, genetic diffusion would suffice to spread novel
genes and gene combinations among the old world hominids.

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