Greetings from the Pacific Northwest:
Three good reads about the interplay
between genetics, nutrition, evolution, and the future. The first attached file is from the
current issue of Scientific American, discussing the role of food and
nutrition in the evolution of the human species and the 2nd is from
the LA Times weekend magazine about the new work Francis Crick, the scientist
who discovered DNA, is doing.
Brain
Power: The Search for Origins
By Sandra Blakeslee, NYT,
11.05.02
Neuroscientists
have found an evocative solution to a classic problem: which is more important
in shaping the human brain, nature or nurture?
Their
answer is complex. The brain is
not primarily the product of genes, they say, but neither is it simply the sum
of one's experiences. Rather,
they say, each human brain is constructed of complex neural circuits that
start taking shape before birth and continue to grow and change throughout
life as genes and cells are influenced by environment, experience and
culture.
There
is widespread agreement that genes and environment interact in brain
development, said Dr. Terrence J. Sejnowski, a neuroscientist at the Salk
Institute in San Diego, and a leading proponent of the new synthesis. The
new idea, he said, is that human cultures, which teach children what to
believe and what to expect in life, interact with cell biology and molecular
genetics to assemble the highly social human
brain.
Though
everyone's brain begins with "a basic scaffold of connectivity that is formed
according to genetic blueprints," said Dr. Carla Shatz, a developmental
neurobiologist at Harvard Medical School, "a baby's brain is not a miniature
of the adult's, but rather is a dynamically changing structure." Experience alters brain structure,
chemistry and gene expression to sculpture immature neural circuits into adult
circuitry, she said.
In
short, the theory's advocates say, while the brain directs people's activities
in everyday life, the activities themselves shape the brain throughout life.
"The
attempt to separate genes and environment is a mistake," said Dr. Steven R.
Quartz, a scientist at the California Institute of Technology. "What makes us who we are is a complex
interplay of early experiences, parenting, birth order, friends, genes and how
these forces interact." He and
Dr. Sejnowski wrote "Liars, Lovers and Heroes," published last month, which
outlines details of what they call cultural biology.
Another
book making similar arguments, "The Origin of Minds," is to be published this
month. Its authors are Dr. Peggy
La Cerra, a neuroscientist and president of a consulting firm in Ojai, Calif.,
and Roger Bingham of the Center for Brain and Cognition at the University of
California at San Diego.
Scientists
and philosophers have argued about the role of culture in shaping the brain
for millenniums. Plato and
Artistotle argued over whether human traits like virtue were inborn or
learned. Darwin's ideas led many
scholars to declare that human traits were inborn, with each racial group at a
different level of evolution, a view that culminated in the unbridled eugenics
of the Holocaust.
The
backlash was an era of cultural relativism, which saw the newborn brain as a
blank slate that evolution had no part in.
A
new battle over human nature began in the 1970's, when Dr. Edward O. Wilson
argued that human behavior, like that of other animals, was a product of the
evolutionary pressures of natural selection. Evolutionary psychologists adopted
this argument, using it to explain everything from sexual differences in
dating behavior to the appeal of potato chips.
The
advocates of the new neurobiological view say it is time to look more closely
at the evidence for evolutionary psychology's position.
"It's
true you can't separate the question of who we are from the world our
ancestors passed through on their way to becoming us," Dr. Sejnowski
said. But that evolution did not
occur in the relatively stable savanna described by evolutionary
psychologists, he said, but rather during a period of unusual, extreme and
rapid oscillations in climate. If
the brain evolved any trait during the Pleistocene, he declared, it was
flexibility.
While
it is true that different brain regions tend to specialize in different
functions, like language or face recognition, Dr. Sejnowski said, these areas
are very changeable and not hard-wired modules.
Humans
are born with temperaments arising from genetic variations in brain chemicals
called neuromodulators, Dr. Quartz said.
These differences may lead one baby to avoid novelty and another to
seek it. But the experiences that
result help construct the growing brain.
Humans
are also born with a very large prefrontal cortex, a higher brain region
involved in planning that taps into an ancient system for predicting what is
rewarding and making decisions to maximize rewards and avoid punishments.
Neuroscientists
are finding that this circuit, which fully matures in late adolescence, is an
internal guidance system that fills each person's world with values, meaning
and emotional tone, taking shape according to a person's
culture.
In
other words, culture contributes not just to the brain's contents but to its
wiring as well, Dr. Quartz said.
http://www.nytimes.com/2002/11/05/health/anatomy/05BRAI.html
Karen Watters
Cole
Outgoing Mail Scanned by NAV
2002
