DOCTOR'S VIEW ARCHIVE

What ARE Little Boys & Girls Made Of?

JACKSONVILLE, FLORIDA-"What are little boys made of? Snips and snails, and puppy dogs' tails; That's what little boys are made of." according to the old nursery rhyme. The next verse, of course, addresses the parallel question: "What are little girls made of? Sugar and spice, and everything nice; That's what little girls are made of."

The behavioral differences between boys and girls continue to be a matter of common wisdom. For example, there was a front-page article in The New York Times on June 15 about the children of Robert F. ("Bobby") Kennedy. The reporter Deborah Sontag noted that, among Bobby's 11 children: "It was accepted that the boys had more problems than the girls, because as Mrs. Kennedy Townsend (the eldest of Bobby's offspring) said, 'boys in general get in trouble more.'"

Do boys "get in trouble more?" Even more basically, do boys and girls engage in different behaviors? If so, why? Is it all learned through our experiences (environmental)? Or, do our genes play a role, perhaps in pre-programming our behavior?

What may be truly different between boys' and girls' behaviors may not have to with boys' snips and snails and puppy dogs' tails or with girls' sugar and spice levels. Instead, it may have to do with differences between their X chromosomes.

That is what is proposed in a provocative study published this week in the eminent British journal Nature (1997;volume 387, page 705). The paper is entitled "Evidence from Turner's syndrome of an imprinted X-linked locus affecting cognitive function."

Boys (XY) always receive their single X chromosome from their mother while girls (XX) receive an X from their mother and an X from their father. As far as X chromosomes go, what separates boys from girls is not only that girls have two X chromosomes but that only girls have an X chromosome from their father (a paternal X).