From THELMA ROWELL and MARY-CLAIRE KING
We should like to reply to ‘The case against Eve’ (22 June), in part
because Allan Wilson, who we know was distressed by the article, was unable
to respond himself before he died in July.
Wolpoff and Thorne seriously misinterpret the evidence from mitochondrial
DNA. The suggestion of replacement of populations, ‘probably in an abrupt
and violent manner’, is theirs, not Wilson’s. Basically, they have confused
the migration and extinction of genes with those of populations.
There is no suggestion that Eve was the first, and at one time the only,
woman. The results of a computer simulation may clarify the picture, as
it did for us. Begin with a population of (say) 15 mothers and set the rules
so that each generation remains the same size and the average number of
daughters produced by each mother surviving to reproduce is one, so that
in each generation some mothers leave no daughters (but any number of sons).
Run the program, and in about 15 generations, the 15 current adult females
will trace their maternal lineage back to a single ancestress; the mitochondrial
DNA of the remaining 14 founder-mothers has become extinct. This happens
without any selection or ‘violent replacement’. It’s just the process of
chance. The time span extrapolated back to the ‘African Eve’ is about 6000
generations.
In general, it seems that in human societies, as in the closely related
chimpanzees, men stay at home, in alliance with their male kin, and import
wives. Thus the mitochondrial DNA moves, with the females, from community
to community, in ordinary marriage transactions.
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In the meantime, nuclear DNA is contributed to the next generation by
men as well as women. If genes controlling skull shape are in nuclear DNA,
which seems probable, they may locally change frequency as a result of drift
or local environmental selection pressures. Thus we see no incompatibility
in the African origin of all human mitochondrial DNA and the local continuation
of distinctive bone structure. The existence of both certainly strengthens
the view of the human race as one single interbreeding population.
A challenge to ‘Eve’ must come from finding mitochondrial DNA somewhere
in the world which does not conform to the patterns of descent proposed
by Wilson’s lab. And the best of luck!
Thelma Rowell, Mary-Claire King University of California at Berkeley
