On Tue, 16 Sep 2003, Barry Groves wrote:

> While our ancestors may have eaten sufficient plant material to supply
> 35-55% of their calories from plant foods before the advent of the Ice Ages,
> there is no way they could have done so during them. With long cold winters
> and short cool summers, for most of the year there would have been very
> little plant material to eat.

Whilst global ice-age climates would have been cooler than today, the
earth's position relative to the sun was very little different to today,
so growing seasons were longer then than now for the same mean
temperature. There is likely to have been plenty of plant material in
those parts of the world where humans resided.  Alfano et al (2003) show
by comparison of biome simulations and pollen data that temperate
grasslands and forests dominated the landscape of southern Europe
(Iberia-Italy-Balkans) in oxygen isotope stage 3.  The availability of
plant foods would probably exceed that of northern Europe today, given
longer growing seasons.  Present-day tropical and sub-tropical areas had
different plant communities in many places to those they have today, but
outside of the expanded deserts plant *productivity* is likely to have
been similar.

Given that genetic evidence shows that until relatively recently the
majority of humans ancestral to modern people lived in sub-Saharan Africa
(Relethford & Jorde 1999), the influence of reduced plant availability in
ice-age northern Eurasia on human evolution is likely to be fairly small.
Even more so when one considers that there is no evidence for modern
humans in this area until after 50,000 years ago.

> Thus I do not accept Cordain's ratios during the last 2.5 million years.
> And that is the time when 99.9% of our present genetic makeup would have
> been formed.

This cannot be true.  We share about 95% of our genetic make-up with
chimpanzees (Britten 2002), from which our species diverged at least 6-7
million years ago.  Only a very small proportion of our genetic make-up
can have evolved in the last 2.5 million years, albeit that important part
which distinguishes us from other species.

References

Alfano MJ, Barron EJ, Pollard D, Huntley B & Allen JRM (2003) Comparison
of climate model results with European vegetation and permafrost during
oxygen isotope stage three.  Quaternary Research 59 97-107

Britten RJ (2002) Divergence between samples of chimpanzee and human DNA
sequences is 5% counting indels.  Proceedings of the National Academy of
Sciences 99 13633-13635.

Relethford JH & Jorde LB (1999) Genetic evidence for larger African
population size during recent human evolution. American Journal of
Physical Anthropology 108 251-260.


Andrew

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 Dr. Andrew Millard                              [log in to unmask]
 Department of Archaeology, University of Durham,   Tel: +44 191 334 1147
 South Road, Durham. DH1 3LE. United Kingdom.       Fax: +44 191 334 1101
                     http://www.dur.ac.uk/a.r.millard/
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