There is a fascinating report which seriously questions the neutral theory
of gene mutation. It can be found in this week's Nature or information about
it at http://www.uchospitals.edu/news/Evolve.html
"A comparison of the A/S ratio of polymorphism in Drosophila melanogaster
with that of divergence from Drosophila simulans shows that the A/S ratio of
divergence is twice as high—a difference that is often attributed to
positive selection. But an increase in selective constraint owing to an
increase in effective population size could also explain this observation,
and, if so, all genes should be affected similarly. Here we show that the
difference between polymorphism and divergence is limited to only a fraction
of the genes, which are also evolving more rapidly, and this implies that
positive selection is responsible. A higher A/S ratio of divergence than of
polymorphism is also observed in other species, which suggests a rate of
adaptive evolution that is far higher than permitted by the neutral theory
of molecular evolution." Justin C. Fay, Gerald J. Wyckoff & Chung-I
Wu,"Testing the neutral theory of molecular evolution with genomic data from
Drosophila" Nature 415(2002), 1024 - 1026
The fascinating thing is that if mtDNA genes are not neutral, then
mitochondrial Eve is history. And some authorities believe that mtDNA is
subject to selection:
"The low levels of human mtDNA diversity have been
used as support for the out-of-Africa replacement
hypothesis (CANN et al. 1987; VIGILANT et al. 1991);
however, directional selection could also explain the
reduced mtDNA diversity in humans compared with chimpanzees
( [pi]= 0.24% for humans and 0.73% for the chimpanzee
subspecies P. t. verus. Table 2). Because there is no
apparent genetic recombination in mtDNA, this depletion of
variation could be the result of an advantageous mutation
anywhere within the mitochondrial genome sweeping through
the human population." Cheryl A. Wise, Michaela Sraml and Simon Easteal,
"Departure from Neutrality at the Mitochondrial NADH
Dehydrogenase Subunit 2 Gene in Humans, but not in
Chimpanzees." Genetics, 148(1998):409-421, p. 419-420
"The interpretation that the departure from neutral
mutation-drift equilibrium reflects population size
expansions assumes selective neutrality for these gene
systems. However, several geneticists have suggested that
selection may influence the distribution of mtDNA and Y
chromosome variation in humans." John Hawks, Keith Hunley
Sang-Hee Lee, and Milford Wolpoff, "Population Bottlenecks
and Pleistocene Human Evolution," Mol. Biol. Evol.,
17(2000):1:2-22, p. 10
What will the ID and RTB folk, who have been claiming that mankind can't be
older than 100-150kyr old, do if Eve dies?
glenn
see http://www.glenn.morton.btinternet.co.uk/dmd.htm
for lots of creation/evolution information
anthropology/geology/paleontology/theology\
personal stories of struggle
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