Darwin-L Message Log 7:44 (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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<7:44>From kent@darwin.eeb.uconn.edu  Wed Mar 16 07:01:49 1994

Date: Wed, 16 Mar 94 08:03:09 EST
From: kent@darwin.eeb.uconn.edu (Kent Holsinger)
To: darwin-l@ukanaix.cc.ukans.edu
Subject: Re: Humanoid fossils in Time

Bayla Singer writes:
>Excuse me: I'm having a bit of trouble visualizing the different time
>scales required for
>	(a) gene-pool mixing via exchange of migrating individuals, which
>          would support the evolution of several populations along
>	    similar/same lines
>	(b) evolution of H erectus to H sapiens being 'finished' at
>	    one site, and spreading with little or no further evolution.
>Spread-and-evolve seems congruent to Evolve-and-spread: why is it not so?
>Would someone please spell this out?

The difference, as I see it, is as follows.  Evolutionary biologists usually
envision species as having a single, geographically restricted place of origin.
Once a species has arisen it may spread from its place of origin, but new
populations are recognizably part of the same species.  There is much debate
about how important continuous gene flow among populations is to retaining a
species identity.  I am highly skeptical about the efficacy of present day
migration in maintaining species identity.  The amount of gene movement between
house sparrow populations in southern California and northern Europe, for
example, must be so small as to be irrelevant.  It seems far more plausible
that a species maintains its recognizable identity because all populations are
(relatively) recent derivatives of a single common ancestor.

In short, the single origin scenario envisions divergence between species in a
single, restricted geographic region.  As applied to human origins, it would
imply the _H. erectus_ and _H. sapiens_ were contemporaneous, for a time, and
that _H. sapiens_  replaced _H. erectus_.

The multiregional hypothesis, as I understand it (and I'm not an
anthropologist, so someone please correct me if I have misunderstood it), is
that _H. erectus_ populations everywhere evolved simultaneously into _H.
sapiens_.  Under this hypothesis _H. erectus_ and _H. sapiens_ were never
contemporaneous, and _H. sapiens_ replaced _H. erectus_ only in the sense
that _H. sapiens_ evolved from _H. erectus_.

Does that help?

-- Kent

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