Darwin-L Message Log 7:40 (March 1994)

Academic Discussion on the History and Theory of the Historical Sciences

This is one message from the Archives of Darwin-L (1993–1997), a professional discussion group on the history and theory of the historical sciences.

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<7:40>From jacobsk@ERE.UMontreal.CA  Mon Mar 14 19:41:59 1994

From: jacobsk@ERE.UMontreal.CA (Jacobs Kenneth)
Subject: Re: H. erectus gene flow (was: Humanoid fossils...)
To: darwin-l@ukanaix.cc.ukans.edu
Date: Mon, 14 Mar 1994 20:41:49 -0500 (EST)

Iain Davidson writes:

> Perhaps some of the geneticists on the list or others would care to comment
> on Alan Thorne's statement about gene flow:
> "Today human genes flow between Johannesburg and Beijing and between Paris
> to Melbourne.  Apart from interruptions from ice ages, they have probably
> been doing this through the entire span of _Homo sapiens_ evolution."
> It has always seemed to me that gene flow is *such* an important part of
> the multiregional evolution hypothesis that it is puzzling that there is
> not some modelling of how it might happen, or some demonstration of the
> sorts of data which might represent it.  Does anyone think it coherent to
> have gene flow from Johannesburg to Beijing at 400 000 years ago, a) in
> principle or b) in practice?

In general, it is probably safest to think in terms of gene flow as always
having been the _rule_ rather than the exception.  Two principle factors act
to mitigate against gene flow between human groups:  geographic barriers and
social barriers.  A good argument has been made that, for most hunter-gatherer
systems, social barriers will not be important.  If anything, social practices
would have as one of their effects the fairly unimpeded flow of genes from one
end of the geographic range of the species to another (restrictions being
solely physiographic in nature; for the essential of this argument, see Wobst,
H.M. 1976, Locational relationships in Paleolithic society.  J Hum Evol. 5:49-
58).  Social barriers to gene flow would have arisen (with instructive
exceptions) most easily with the advent of food production, when  local
populations size and density could go up.  The genetic effects of the kind of
open mating networks (i.e., the implications of the gene flow) implied here
were explored nicely in:  Weiss, K.M. & T. Maruyama 1976, Archaeology,
population genetics and studies of human racial ancestry.  Am. J Phys. Anthrop.

	Note that the above models apply solely to pre-food production hunter-
gatherer systems.  Once closed mating networks, as would have been associated
with central-place dominated food producers, started to clutter up the land-
scape, the situation was irretrievably changed.  Whether Homo erectus
can be considered a pre-food production hunter-gatherer, or just a Binfordian
serendipitously foraging beastie is a question for another day.

Ken Jacobs

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