News: Where Is Human Evolution Heading?

Where Is Human Evolution Heading?

http://www.usnews.com/articles/science/2008/07/24/where-is-human-evolution-heading.html

The race's DNA is changing faster than ever; what it means for our
descendants

By Nancy Shute
Posted July 24, 2008

If you judge the progress of humanity by Homer Simpson, Paris Hilton,
and Girls Gone Wild videos, you might conclude that our evolution has
stalled?or even shifted into reverse. Not so, scientists say. Humans
are evolving faster than ever before, picking up new genetic traits
and talents that may help us survive a turbulent future.

Much remodeling has gone on since the dawn of agriculture about 10
millenniums ago. "People who lived 10,000 years ago were much more
like Neanderthals than we are like those people," says John Hawks, a
professor of anthropology at the University of Wisconsin. "We've
changed."

Hawks is among a growing number of scientists who are using
whole-genome sequencing and other modern technologies to zero in on
just how we've changed. Their research is helping illuminate not only
how humans became what we are but also where we might be headed. For
instance, some scientists speculate that changes in human mating
patterns may be contributing to the increase in autism. Others track
how humans have morphed in response to changing circumstances,
including enhanced abilities to metabolize sugar and fight disease.
Some people are genetically more resistant to the HIV virus, for
instance, and that trait should become more common in the future, as
those people are more likely to survive and have children who are
resistant. Yet for some people, the makeover isn't big enough or fast
enough. Some parents have started using DNA testing to choose the
genetic makeup of their children, rejecting embryos with inherited
flaws or embracing those with desired traits?such as being the right
sex.

New mutations. Until recently, anthropologists thought that human
evolution had slowed down. But last December, Hawks reported that it
has actually accelerated 100-fold in the past 5,000 to 10,000 years.
He figured that out by comparing chunks of DNA among 269 people from
around the world. Over time, DNA accumulates random mutations, just as
the front of a white T-shirt tends to accumulate spots. The bigger the
chunks of DNA without random spots, the more recently it had been
minted. Using this system, Hawks concluded that recent genetic changes
account for about 7 percent of the human genome. Much of the increase,
he says, has been fueled by the growth of the world's population,
which has expanded by a factor of 1,000 over the past 10,000 years.
Having more people increases the odds of mutations.

At the same time, the human genome has been scrambling to adapt to a
rapidly changing world?11,000 years ago, nobody farmed, nobody milked
domesticated animals, and nobody lived in a city. People with a
mutation that aided survival were more likely to thrive, reproduce,
and pass that mutation along to offspring. For example, the capacity
to digest lactose, the sugar in milk, has become common only over the
past 3,000 years. Now, about 95 percent of the people in northern
Germany have the mutation, which also popped up independently among
the Masai in Africa and the Lapps in Finland. Hawks says: "This is
really rapid evolution."

Humans will continue to change to cope with new diseases, if history
is any guide. Genes that defend against infectious disease have been
among the most rapidly evolving parts of the human genome. People
whose ancestors lived in European cities are more likely to have some
resistance to smallpox, while people in sub-Saharan Africa are more
likely to be genetically resistant to malaria. Just weeks ago,
researchers reported that one genetic variant that protects against
malaria also makes people more susceptible to AIDS, a discovery that
could lead to tailored treatment for AIDS in Africa.

Right now, our genes are playing catch-up against modern scourges?like
diabetes. Native Americans and Polynesians, whose cultures only
recently adopted a European-style diet of refined grains, have the
world's highest rates of diabetes. The theory is that the "thrifty
genes" that helped those groups survive famines haven't had time to
adapt to the glucose spikes caused by eating starchy food. "How we
move sugars around and how we burn them has really changed a lot,"
says Gregory Wray, an evolutionary biologist at Duke University.

It's even possible that very recent changes in society and the
workplace could underpin the recent rise in cases of autism. Simon
Baron-Cohen, director of the Autism Research Centre at the University
of Cambridge, was struck by how many of the parents of children with
autism who he tested were really good "systematizers"?people who
understand the world according to rules or laws. They also were more
likely to have a father who worked in engineering. He wonders if the
increase in autism diagnoses could be partly due to "assortative
mating"?that is, people picking mates like themselves. People with
autism spectrum disorder are often detail oriented and analytical, and
today they might have an easier time finding a spouse with similar
abilities than they would have in past eras. Baron-Cohen notes that in
the late 1950s, only 2 percent of the undergraduates at Massachusetts
Institute of Technology were women; now, 50 percent are. So, he's
setting up a study to test whether assortative mating among people
with a genetic predisposition for autism could be fueling the birth of
more children with autism.

The human brain, which has evolved into a cognitive machine unique in
the world, is likely to change even more in the future. Our niche in
nature, says Stephen Pinker, an experimental psychologist at Harvard
University who studies the evolution of language and the mind, is the
"cognitive niche." In research published last year, Wray identified
genes that control glucose metabolism in the brain as among those most
recently evolved. Those changes may have been essential to fueling the
human brain's growth to a size twice that of our nearest cousin, the
chimpanzee. "If you make a big brain, it's an energy hog," Wray says.
"It's like putting a V-8 engine in a tiny little car." It could also
help explain why chimpanzees don't get diabetes, while humans do.

Tinkering. Take that souped-up brain and put it in the texting,
Twittering, 24-7 world we've recently created for ourselves, and it's
easy to imagine that we will become superspeedy multitaskers?or more
complacent cubicle dwellers. However, this progress comes too slowly
for some. "The world is changing so rapidly that biological evolution
is not where the action is," says Nick Bostrom, a professor at the
University of Oxford and cofounder of the World Transhumanist
Association, which seeks to use science to improve humankind. He, for
one, doesn't care to wait through a few hundred generations for
improvements. Genetic engineering will help short term, he says, and
then nanotechnology will step in, altering the biochemistry of the
human body at the flip of a switch. "If we're thinking several hundred
years out, then much more radical intervention may be feasible."

Unfortunately for those like Bostrom, who see humans as one big
fixer-upper project, the human genome has so far proved to be
remarkably resistant to tinkering. Since 1990, when gene therapy was
first tested in humans, doctors have been trying to repair defective
genes by injecting healthy ones. The method has shown only limited
success and has failed to deliver as a treatment for common conditions
such as heart disease. And gene therapy fixes only somatic genes,
which aren't inherited. Germline therapy, which would create heritable
mutations, is a far more complex?and contentious?challenge.

Notwithstanding the obstacles, Bostrom's wish list for improved human
traits includes a longer "health span," with fewer years of human life
spent struggling against cancer, heart disease, and dementia. Enhanced
cognitive abilities would be nice, too. "Perhaps physical
attractiveness would be a popular trait," he says.

There's as yet no way to select for attractiveness, but parents can
choose a few of an offspring's genes if they're willing to try
preimplantation genetic diagnosis. In PGD, doctors carefully vacuum a
single cell from a 3-day-old embryo and test certain genes before
deciding whether to place the embryo into a woman's uterus. The
technique, which must be used in combination with in vitro
fertilization, was invented almost 20 years ago as a way to reduce the
odds of a child inheriting a deadly genetic disorder, such as
Tay-Sachs.

It didn't take long for prospective parents to realize that the same
method could be use to sort embryos for other reasons. Since 2000,
parents have been able to use PGD to choose an embryo's tissue type,
so that the ensuing child could serve as a stem cell or bone marrow
donor to a sick sibling. More recently, a few have used PGD to reject
embryos that have genes that merely increase the risk of disease in
adulthood, such as the BRCA breast cancer genes. A few parents with
disabilities such as deafness have used PGD to choose a deaf child.
And PGD is increasingly used to reject embryos that have no problems
at all?unless you consider being the wrong sex a problem. A number of
fertility clinics in the United States advertise PGD to parents who
want to be guaranteed the child will have the sex they choose. One
California clinic boasts of "over 3,800 cases: 100 percent sex
selection success." With PGD largely unregulated in the United States,
it doesn't take a Nobel Prize in genetics to imagine that babies could
soon be ordered up in custom sizes and colors, like a Mini Cooper.

The next step: children with genes from three parents. In the late
1990s, IVF clinics started injecting cytoplasm from younger women's
eggs into those of older women, in an effort to increase the odds of
pregnancy. About 30 babies have been born worldwide as a result, and
those children carry genes from both women. But that rejiggering of
the human germline was almost inadvertent. Scientists are now
intentionally making that mix. Earlier this year, researchers at
Newcastle University in England deliberately created human embryos
that had DNA from one father and two mothers, in order to avoid the
risk of a mitochondrial disease from the original mother.

But it's too early to lie awake worrying that genetically manipulated
superkids are going to ace your grandkids out of varsity soccer, says
Thomas Murray, a bioethicist and president of the Hastings Center.
"Our capacity to do these kinds of intentional designs is vastly
overrated." But, he says, it's not too early to start thinking about
what's really important about being a parent. The traits that people
most value, Murray says?being smart, being kind, being a successful
competitor?are the ones least likely to be determined by a few
tweakable genes. For that kind of control over the next generation, it
still takes good old-fashioned nurturing, teaching, and love.

--
Bob.

.

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