/-------------------- advertisement -----------------------\
Explore more of Starbucks at Starbucks.com.
http://www.starbucks.com/default.asp?ci=1015
\----------------------------------------------------------/
The End of Evolution?
August 24, 2003
By NICHOLAS WADE
The most improbable item in science fiction movies is not
the hardware - the faster-than-light travel, the tractor
beams, the levitation - but the people. Strangely, they
always look and behave just like us. Yet the one safe
prediction about the far future is that humans will be a
lot further along in their evolution.
Last week population geneticists, rummaging in DNA's
ever-fascinating attic, set dates on two important changes
in the human form.
Dr. Alan R. Rogers of the University of Utah figured out
that the ancestral human population had acquired black
skin, as a protection against the sun, at least 1.2 million
years ago, and therefore that it must have shed its fur
some time before this date.
Clothing came long after we were naked. Dr. Mark Stoneking,
of the Institute for Evolutionary Anthropology in Leipzig,
managed to address this question by calculating when the
human body louse (which lives only in clothing, not hair)
evolved from the human head louse. That proud event in
human history dates to between 72,000 and 42,000 years ago,
Dr. Stoneking reported
So where do we go from here? Have we attained perfection
and ceased to evolve?
Many geneticists think that is very unlikely, though few
find it easy to say where we are headed or how fast. Until
the agricultural revolution 10,000 years ago, people used
to live in small populations with little gene flow between
them. That is the best situation for rapid evolution, said
Sewall Wright, one of the founders of population genetics.
But Sir Ronald A. Fisher, another founder of the
discipline, argued that large populations with random
mating - just what globalization and air travel are helping
to bring about - were the best fodder for rapid evolution.
"Which of them is right? No one really knows," Dr. Rogers
said.
Considering that the common ancestor of humans and
chimpanzees lived only 5 to 6 million years ago, human
evolution seems to have been quite rapid. The chimp, our
closest living relative, is still a standard ape, whereas
we have become a truly weird one. And our evolution put on
an extra spurt just 50,000 years ago, the date when we may
have perfected language, made our first objets d'art and
dispersed from our ancestral homeland some place in
northeast Africa.
Despite the medical advances and creature comforts that
shelter people in rich countries, natural selection is
still hard at work. Microbes and parasites still nip at our
heels, forcing the human genome to stay in constant motion.
It is clearly in the throes of adapting to malaria, a
disease that seems to have struck only in the last 8,000
years, and the protective gene that has sickle cell anemia
as a side effect is a sign of a hasty patch.
It seems reasonable to predict that the human physical form
will stay in equilibrium with its surroundings. If the
ozone layer thins, pale skins will be out and dark skins de
rigeur. If climate heats up, the adaptations for living in
hot places will spread, though it could take tens or
hundreds of generations for a new gene to become
widespread.
Sexual selection, too, is busily at work. This powerful
process, first recognized by Darwin, works on traits that
are attractive to other sex, and help the owner's genes
spread into the next generation. The peacock's tail, a
wonder of the natural world, has been created by the sexual
preference of generations of peahens.
Human skin color and hair distribution may be pale echoes
of the same process. Recent social changes may have
accelerated the pace of sexual selection. "You used to
marry a lass from your local village, now it's anyone you
can track down on the Internet," said Dr. Mark Pagel, an
evolutionary biologist at the University of Reading in
England.
Though features like the peacock's tail are chosen for
aesthetic, or arbitrary, reasons, they often seem to be
correlated with health, and indeed their owners are chosen
as mates because these features subliminally advertise a
good immune system or freedom from parasites. So if sexual
selection in people becomes more intense as people have a
wider choice of mates, that suggests a terribly Panglossian
forecast: we will become more healthy and ever more
beautiful.
Most animals struggle to survive in a harsh environment,
beset by accidents and predators. Humans got that problem
largely under control long ago but live in a fiercer jungle
- that of a human society. Indeed, social intelligence -
the ability to keep track of a society's hierarchy and what
chits an individual owed to others or had due - may have
been a factor in the increase of human brain size. As the
prevalence of Caesareans suggests, the circumference of
babies' brains seems to have gotten as large as
circumstances permit. Will requirements for extra neural
circuitry make our descendants into coneheads? Doubtless,
sexual selection will maintain a decorative swatch of hair
on top.
Society, and the knowledge needed to survive in it, seems
to get ever more complex, suggesting that human social
behavior will continue to evolve. Unfortunately, evolution
has no concept of progress, so behavioral change is not
always for the better. "I suspect that our social behavior
evolves rapidly but that much of it changes direction over
time," said Dr. Henry C. Harpending, an evolutionary
anthropologist at the University of Utah.
Warrior societies like the Yanomamo of South America give
reproductive success to the man who is "violent, scary and
effective at male-male conflict," whereas among peasant
farmers, the successful male would be one who feeds his
children and passes on an estate to them, Dr. Harpending
said.
A dramatic instance of the former process came to light
earlier this year with the discovery that no less than 8
percent of men who live today in the former domains of the
Mongol empire carry the Y chromosome of Genghis Khan and
the Mongol royal house. It is hard to see a Genghis having
much reproductive success in modern societies. Perhaps
another Panglossian prediction is called for: in a more
ordered society, evolution will favor the fostering type of
male over the Yanomamo-style brutes.
Not everything is roses in evolution's garden. Ronald
Fisher, the British biologist, pointed out in 1930 that the
genes for mental ability tend to move upward through the
social classes but that fertility is higher in the lower
social classes. He concluded that selection constantly
opposes genes that favor creativity and intelligence.
Fisher's idea has not been proven wrong in theory, although
many biologists, besides detesting it for the support it
gave to eugenic policies, believe it has proven false in
practice. "It hasn't been formally refuted in the sense
that we could never test it," Dr. Pagel said. Though people
with fewer resources tend to have more children, that may
be for lack of education, not intelligence. "Education is
the best contraceptive. If you brought these people up in
the middle class they would have fewer children," Dr. Pagel
said. "Fisher's empirical observation is correct, that the
lower orders have more babies, but that doesn't mean their
genotypes are inferior."
Given all the possibilities for human evolutionary change,
it is hard to know which path our distant descendants will
be constrained to tread. From a New York perspective,
however, it is hard to ignore a certain foreboding: that
under the joint power of sexual selection and Fisher's
gloomy prognosis we will become ever more beautiful and
less acute. The future, in a word, is Californian.
http://www.nytimes.com/2003/08/24/weekinreview/24WADE.html?ex=1062839277&ei=1&en=e028715eaedbc443
---------------------------------
Get Home Delivery of The New York Times Newspaper. Imagine
reading The New York Times any time & anywhere you like!
Leisurely catch up on events & expand your horizons. Enjoy
now for 50% off Home Delivery! Click here:
http://www.nytimes.com/ads/nytcirc/index.html
HOW TO ADVERTISE
---------------------------------
For information on advertising in e-mail newsletters
or other creative advertising opportunities with The
New York Times on the Web, please contact
[EMAIL PROTECTED] or visit our online media
kit at http://www.nytimes.com/adinfo
For general information about NYTimes.com, write to
[EMAIL PROTECTED]
Copyright 2003 The New York Times Company
--------------------------------------------
This service is hosted on the Infocom network
http://www.infocom.co.ug
