Everybody agrees that being socially skilled means—in part at least, nowadays—being sensitive to another person’s feelings. And most people would probably agree that women tend to be more socially skilled than men. What most people probably wouldn’t agree on is that the skill is genetically based. But last June child psychiatrist David Skuse of the Institute of Child Health in London and a team of psychologists and geneticists proposed exactly that: genetic information influencing social skills, they claim, lies somewhere on the X chromosome. Even more surprising, these skills seem to be handed off to women by the X chromosome they inherit not from their similarly gracious mothers but from their clueless fathers.
Skuse came to this tentative conclusion after studying 80 females with Turner’s syndrome, a genetic disorder in which a girl inherits only one X chromosome from either her mother or her father. Turner’s girls lack ovaries, but they don’t look much different from normal girls, who inherit an X chromosome from both parents. In most respects, including verbal intelligence, they are normal.
Except that psychological tests suggest many of them have poor social skills. Skuse decided to investigate whether inheriting an X from the mother or from the father had any influence on that problem. The idea isn’t as strange as it sounds. A handful of genes have been identified whose expression is dictated by parental origin; they are called imprinted genes. So far, though, nobody has found evidence of an imprinted gene on a human sex chromosome.
A close look at the girls’ X chromosomes showed that 55 had a maternally derived X chromosome and 25 had a paternally derived X. When Skuse gave the parents a questionnaire designed to measure their child’s social skills, girls with the maternal X had scores indicating poor social skills; in general, they were unaware of others’ feelings and had trouble picking up social signals, at least according to their parents. In contrast, the girls with the paternal X were far more socially adept. Moreover, when Skuse tested the girls’ ability to concentrate by asking them to substitute ones for twos and twos for ones in a string of ones and twos, he found that the girls with the maternal X were less able to concentrate on this unusual task. He concluded that their thinking was more impulsive, which might contribute to their social difficulties.
The differences between the two Turner’s groups, says Skuse, hint that somewhere on the X lies a gene (or genes) influencing social ability—one that is expressed only if it is inherited from the father. The father, in turn, must get the gene from his mother because men always inherit their X chromosome from their mothers and their Y chromosome from their fathers. In men, however, the gene does not seem to be turned on; boys score badly on Skuse’s social skills questionnaire compared with normal girls. Only girls, who inherit an X from their fathers, express the gene. In Skuse’s scenario, the social skills trait passes from mother to son to granddaughter, but with the male acting only as an asymptomatic carrier.
Skuse thinks this peculiar pattern of inheritance—if it does turn out be real—has evolutionary significance. The imprinting mechanism evolved for a good reason, he says. If it happened, it meant that mothers now conferred an advantage on their sons. Why would it be advantageous for boys not to express this social skills gene? This is where we enter a very speculative realm, says Skuse. I really don’t know. It must have enabled those males to become more dominant. And I suspect it may also have enabled a more uniform social structure to be imposed on a group of males who would have had to learn social skills rather than develop them intuitively.