Re: Brain size, IQ

11 Sep 1996 13:38:30 GMT

Gerold Firl ( wrote:
: In article <>, (Richard Foy) writes:

: |> In article <50nadd$>,
: |> Gerold Firl <> 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.

I've seen some similar studies, and the results are order of magnitude
correct. The gene flow is low enough that local populations can maintain
their local characteristics, but any truly advantageous combination of
genes can spread relatively rapidly. It does suggest that the neanderthal
populations of western Eurasia were isolated for at least a while, since
male humans seem not be be fussy about who or what they have sex with.
The variation seen about 2 MYr BP in East Africa is very interesting in
this context.

Harry Erwin, Internet:, Web Page:
49 year old PhD student in computational neuroscience ("how bats do it" 8)
and lecturer for CS 211 (data structures and advanced C++)