SAN FRANCISCO — Is your child shy? Timid? Afraid of meeting new people, trying new foods or visiting unfamiliar places?
Those childhood fears and temperamental traits may be built into the same kinds of genetic instructions that affect height, hair color or predisposition to disease, according to new evidence presented Saturday by several research groups at the annual meeting of the American Assn. for the Advancement of Science.
Although none of the researchers has found any direct genetic link to human behavior, their work indicates that such traits are a matter of inborn biology, not improper parenting.
"There are many American parents who blame themselves when they have a 5-year-old child who is timid or shy," said Harvard University psychologist Jerome Kagan, who presented his own research on the genetics of inhibited children. The new research means, he said, "a sizable burden of guilt is lifted."
The controversial research, which examines the genetic underpinnings of human behavior and temperament, is a tantalizing hint of a future in which scientists may have biological and chemical markers for a range of inherited temperamental moods, from sadness and disgust to awe and astonishment. If confirmed by other studies, the work has serious implications for child-rearing, teaching and psychotherapy.
By mapping the brain wave activity of infants and toddlers, researchers at the University of Maryland have developed a set of brain wave patterns they can use to predict what type of temperament an infant will develop: cautious and reserved or adventurous and uninhibited. Fussy, fidgety babies showed a distinctive brain wave pattern involving the right side of their brains.
"These infants are more likely to be fearful, intimidated and, in later life, shy and timid," said Nathan Fox, a Maryland professor of human development who conducted the study. "What we are saying is that when it comes to personality, we do not start with a blank slate."
Scientists at the University of Wisconsin in Madison said other research presented at the meeting Saturday showed that traits such as shyness, fear and distress may be more likely to be caused by inherited genetic characteristics than more positive attributes such as pleasure or confidence.
From a separate study of 700 sets of twins, scientists at the University of Wisconsin presented evidence that at least during infancy those temperamental traits are more influenced by biology than by the experiences the children share with their siblings.
Life simply makes some children shy, the scientists emphasized. Experience is enough to make some people more cautious than others. But a significant number may be born with a brain chemistry that makes them that way, they said.
"The human brain contains at least 150 different chemicals," Kagan said. "Everybody has them in different concentrations--a million different kinds of tomato soup. They determine the firing patterns of the brain's neurons."
The idea that a person's frame of mind and disposition may be inherited has been a subject of passionate debate in recent years.
Earlier studies of the sometimes startling similarities between twins have strongly suggested that the genes children inherit are not just responsible for shaping physical development, but also emotional and intellectual tastes. Such research is inconclusive and many scientists disagree on what it may mean.
On several occasions in recent years, scientists have announced the discovery of a gene responsible for controlling some aspect of human behavior, such as schizophrenia or manic depression, only to withdraw their findings after additional scientific scrutiny.
Other genetic influences may be validated after more research. Several studies have linked homosexuality to a gene on the human X chromosome. More recently, researchers linked a rare mutant gene to a family's predisposition to aggressive and violent behavior.
Several researchers Saturday went out of their way to downplay the importance of heredity in shaping human emotional traits, noting that a child's environment plays an important role in tempering or eliminating inborn emotional traits.
The studies found no difference in how infants of either sex inherited a tendency toward shy or timid behavior. More boys, however, often seemed to shed innate timidity--in response perhaps to societal pressure, the researchers said.
"For many, but not all personality characteristics, about 40% to 60% seems to be genetic," said H. Hill Goldsmith, the behavioral geneticist who conducted the Wisconsin research. "But it is a fallacy to believe that any behavior that is genetically inherited cannot be modified over a lifetime."
Some researchers suggested that parents and policy-makers overestimate how much they can do to change a child's personality.
"The family environment is not a crucible, able to mold children in any one developmental direction," said David C. Rowe of the University of Arizona School of Family & Consumer Resources, who studies the genetic origins of anxiety and hyperactivity.
"Exposure to warm and loving parents will not make a shy child less and less shy; nor will exposure to highly active parents make an inactive child more and more active."