Nature Plus Nurture
Equals Destiny
Genes strongly influence behavior but do
not control it
by ROBERT S. BOYD
Knight Ridder Newspapers
(May 7, 2003) -- Now that the human genome - the sum of
all our genes - has been decoded, does it appear that a person's destiny is
fixed for all time in the letters of his or her DNA?
Can a child's future be read out like a bar code on a box of cereal? Was he
doomed from conception to be violent, an alcoholic, a star athlete? Will she be
shy, depressed, superintelligent? Has the genetic revolution left any room for
free will and individual responsibility?
A battery of geneticists, psychologists, philosophers and legal experts
debated these deeply controversial questions at a recent conference on
behavioral genetics, the study of genes and human behavior.
The consensus was clear: Genes strongly influence behavior but do not
control it. Neither does a person's environment - family, upbringing, life
experiences - completely determine who he or she will turn out to be.
"Genes make certain behaviors more likely, but genes don't
automatically lead to actions," said Gregory Kaebnick, co-director of a
National Institutes of Health-sponsored project on genetic ties and the future
of the family. "We can still believe in free will."
"Genes set the stage, but our brains - not our genes - ultimately
control our behavior," said Stephen Hyman, former director of the National
Institute of Mental Health in Bethesda, Md.
"We should not use the genome sequence as a bar code," said
Hyman, now the provost of Harvard University. "There is no such thing as a
gene for grumpiness or for a serial killer."
Arguments about genes and behavior keep popping up as society wrestles with
such difficult issues as whether to execute someone who is mentally ill or
whether homosexuality is inborn or a matter of choice. The conference,
sponsored by the American Association for the Advancement of Science and NIH,
was an effort to explore the best current thinking.
During the last century, scientific opinion swung radically between genetic
determinism - the belief that genes control everything - and environmental
determinism, the notion that behavior is molded, for good or ill, primarily by
parents, homes, schools and neighborhoods.
Now the pendulum has settled between those extremes. "Both
environmental and genetic determinism are wrong," McGue declared.
According to Hyman, your brain builds a complex web of personality traits
by combining internal genetic instructions inherited from your parents and
external signals received from your surroundings. Personality is shaped and
re-shaped over a lifetime.
"We are complex enough to be free from predictability," said Eric
Turkheimer, a psychologist at the University of Virginia in Charlottesville.
Experts at the conference discussed burning moral and legal issues, such as
whether a person with a genetic defect, such as schizophrenia or mental
retardation, should be held responsible for his or her actions.
The conferees were shown a video in which well-known defense lawyer Johnnie
Cochran argued that a client could not be blamed for a murder he committed
while drunk because he had a genetic predisposition to alcoholism.
Neither bad genes or a bad environment can "free offenders from
responsibility for their crimes," said Harold Edgar, a professor of
criminal law at
Columbia University in New York. "To say `I had a hard life' is not an
adequate defense."
Disease is also a product of both genes (sometimes known as nature) and
environment (sometimes known as nurture). For example, genes may make a woman
more likely to get breast cancer or a man prostate cancer, but environmental
factors, such as diet or smoking, play a large role.
"Most diseases have important environmental components," said Dr.
Kenneth Schaffner, an expert on medical ethics at George Washington University
in Washington, D.C. "It's not just the genes."
Schaffner summed up the dominant view: "The nature OR nurture debate
concludes with a nature AND nurture answer."
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