Modern Life's Pressures May Be Hastening Human Evolution

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McClatchy Newspapers

Modern Life's Pressures May Be Hastening Human Evolution

by
Robert S. Boyd

WASHINGTON - We're not finished yet. Even today, scientists say
that human beings are continuing to evolve as our genes respond to
rapid changes in the world around us.

In fact, the pressures of modern life may be speeding up the pace of
human evolution, some anthropologists think.

Their
view contradicts the widespread 20th-century assumption that modern
medical practice, antibiotics, better diet and other advances would
protect people from the perils and stresses that drive evolutionary
change.

Nowadays,
the idea that "human evolution is a continuing process is widely
accepted among anthropologists,'' said Robert Wald Sussman, the editor
of the Yearbook of Physical Anthropology at Washington University in
St. Louis.

It's even conceivable, he said, that our genes
eventually will change enough to create an entirely new human species,
one no longer able to breed with our own species, Homo sapiens.

"Someday
in the far distant future, enough genetic changes might have occurred
so that future populations could not interbreed with the current one,''
Sussman said in an e-mail message.

The still-controversial
concept of "ongoing evolution'' was much discussed last week at the
annual meeting of the American Association of Physical Anthropologists
in Chicago.

It's also the topic of a new book, "The 10,000 Year
Explosion,
'' by anthropologists Henry Harpending and Gregory Cochran of
the University of Utah, Salt Lake City.

"For most of the last
century, the received wisdom in the social sciences has been that human
evolution stopped a long time ago,'' Harpending said. "Clearly,
received wisdom is wrong, and human evolution has continued.''

In
their book, the Utah anthropologists contend that "human evolution has
accelerated in the past 10,000 years, rather than slowing or stopping.
. . . The pace has been so rapid that humans have changed significantly
in body and mind over recorded history.''

Evolutionary changes
result when random mutations or damage to DNA from such factors as
radiation, smoking or toxic chemicals create new varieties of genes.
Some gene changes are harmful, most have no effect and a few provide
advantages that are passed on to future generations. If they're
particularly beneficial, they spread throughout the population.

"Any
gene variant that increases your chance of having children early and
often should be favored,'' Cochran said in an e-mail message.

This
is the process of "natural selection,'' which Charles Darwin proposed
150 years ago and is still the heart of modern evolutionary theory.

For
example, a tiny change in a gene for skin color played a major role in
the evolution of pale skin in humans who migrated from Africa to
northern Europe, while people who remained in Africa kept their dark
skin. That dark skin protected Africans from the tropical sun's
dangerous ultraviolet rays; northerners' lighter skin allowed sunlight
to produce more vitamin D, important for bone growth.

Another set of gene variants produced a different shade of light skin in Asia.

"Asians and Europeans are both bleached Africans, but they evolved different bleaches,'' Harpending said.

Despite modern medical and technological advances, the pressures that lead to evolution by natural selection have continued.

The
massive AIDS epidemic that's raging in southern Africa, for example, is
"almost certainly'' causing gene variants that protect against HIV, the
virus that causes AIDS, to accumulate in the African population,
Harpending said.

When he was asked how many genes currently are
evolving, Harpending replied: "A lot. Several hundred at least, maybe
over a thousand.''

Another anthropologist, John Hawks of the
University of Wisconsin-Madison, said, "Our evolution has recently
accelerated by around 100-fold.''

A key reason, Hawks said, is
the enormous growth of the world's population, which multiplies the
size of the gene pool available to launch new varieties.

"Today,
beneficial mutation must be happening far more than ever before, since
there are more than 6 billion of us,'' Cochran said.

The changes
are so rapid that "we could, in the very near future, compare the genes
of old people and young people'' to detect newly evolving genes,
Cochran said. Skeletons from a few thousand or even a few hundred years
ago also might provide evidence of genetic change.

"Human
evolution didn't stop when anatomically modern humans appeared or when
they expanded out of Africa,'' Harpending said. "It never stopped.''

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