The influence of genes vs. environment's impact

Your artistic talent. Your generally upbeat personality. Your sensitive nature. Your SAT scores. According to scientists, they're in your genes.

For many of us, that's a disturbing notion. We believe all people are created equal; we enshrine the notion that we can all pull ourselves up by the bootstraps. Babies' brains, we like to think, are like blank slates -- chalkboards that get filled in by externals such as nutrition, education, nurturance, the general environment.


So it's nice to know that the very same scientists who talk about the genetic roots of mental and emotional traits also believe in the powerful impact of environment.

"Genes are probably related to most of the major dimensions; there's a real question about how much they're related," says Paul Costa, Ph.D., chief of the Laboratory of Personality and Cognition at the National Institute on Aging. Dr. Costa is also an associate professor of psychology at the Johns Hopkins Medical Institutions and a clinical professor of psychology at Georgetown University's School of Medicine.


"Just about anything we measure shows genetic influence," says Robert Plomin, Ph.D., director of the Center for Developmental and Health Genetics at Penn State University. "But although the genetic influence is significant, the importance of non-genetic influences must also be recognized."

Scientists involved in studying the genetics of personality base their conclusions in large part on studies of adopted children, reared without contact with their biological parents, and identical twins who grow up apart. Over and over again, these people show similarities that defy the odds for pure coincidence.

But they also show differences.

"None of the correlations ever exceed 50 percent," Dr. Plomin says. "So at least 50 percent of the differences between people must be non-genetic."

The question, of course, is: What in the environment is important?

The answer is: Almost everything. Maternal nutrition, drug and alcohol use, nutrition, prematurity, obstetrical complications, attention, affection and education.

"I don't think [talent] comes out of the blue," says Nancy Segal, Ph.D., assistant director of the Minnesota Center for Twin and Adoption Studies.

"But there have to be the facilities that allow expression of the talent; the artist needs an easel, the musician needs an instrument. The great stars will tell you that despite their seemingly natural ability, they need instructors and people to support them."


In other words, the individual is not a product of nature or %J nurture, but of nature and nurture.

"Genetics only convey a range of possibilities and potentialities," says Dr. Costa. "What gets developed or actualized are a function of the prenatal and postnatal environment. It's tempting to think of the genes, but all they do is limit the possibilities."