Nature Plus Nurture
Equals Destiny

Genes strongly influence behavior but do not control it

by ROBERT S. BOYD
Knight Ridder Newspapers

(May 7, 2003 - Washington, D.C.) -- 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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