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New Study Shows Greater Role For Natural Selection
This is really interesting (to me anyways)
Researchers from the University of Chicago have demonstrated that natural
selection plays a much larger role in molecular evolution than anyone
suspected. Their report, published in the February 28 issue of Nature,
shows that about 25 percent of genes are evolving rapidly in response to
competitive pressures. A second paper in the same issue confirms this
Although these papers focus on fruit flies, a previous report from the
Chicago authors found a similar role for positive and negative selection
on the human genome. Data from the previous study (Genetics, July 2001)
allowed them to estimate the number of fixed "good" mutations, which
distinguish humans from monkeys, and the number of residual "bad"
mutations, genetic flaws that have piled up in the genome and are slowly
These papers directly conflict with the "neutral theory," which has
dominated genetic research since the 1960s. According to the neutral
theory, many small genetic changes randomly occur, but the vast majority
simply don't matter. Fewer than one percent make enough of a difference
that they are either embraced or expunged by natural selection.
To measure the importance of selection at the genetic level, Wu and his
former graduate students Justin Fay, Ph.D., and Gerald Wyckoff, Ph.D.,
tallied the minute variations within each of 45 genes among flies of one
species (Drosophila melanogaster) and contrasted them with the same genes
from a different species (Drosophila simulans).
They found that competitive pressures were shaping about one out of four
genes. Thirty-four of the 45 genes, or about 75 percent, showed no sign of
natural selection. But, 11 genes, or about 25 percent showed evidence of
ongoing rapid evolution. These genes contribute disproportionately to the
total number of changes, says Wu.
Most of these genes, note the authors, are involved in processes such as
disease resistance or sexual reproduction, areas where there is
"continually room for improvement."
By studying variation within human genes and comparing them with genes
from old-world monkeys, Wu's team has found that the survival of the
fittest is just as active in humans.
By comparing variation within the human genome and divergence from our ape
ancestors, the researchers determined that about 35 percent of the
accumulated changes were "good."
"The proportion is shockingly high," said Wu, "for someone like myself who
grew up in the neutralist era." It means one advantageous substitution has
entered the human genome every two centuries since humans separated from
monkeys 30 million years ago.
The neutral theory, proposed bygeneticist Motoo Kimura in 1968, was
initially controversial but slowly gained near-gospel status. ...
So Kimura developed a mathematical framework to explain how evolution
worked at the genetic level. He argued that the great bulk of DNA changes
were neutral, biologically insignificant consequences of random mutation,
and seldom if ever driven by natural selection.
Up to 35% could be beneficial? Wow.