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"It's a boy!" announces the doctor to the exhausted mother, a determination the physician makes instantly. And most of the time, the observed sex of an infant does match the genetic sex--with two X chromosomes producing a girl, and an X plus a Y resulting in a boy.

But in the rare cases where they do not, when prenatal development goes awry and genetic boys are born looking more like girls or vice versa, physicians and parents generally assign the newborn a sex. Most often the child becomes female, because female genitals are easier to construct, says William G. Reiner, MD, a child psychiatrist and urologist at the University of Oklahoma health services center.

The prevailing theory behind this long-standing practice, says Reiner, has been that a person reared as a girl will eventually embrace that category. Now, however, new research by Reiner suggests that perhaps such assumptions ought not to be made. A study by Reiner and John Gearhart, MD, of Johns Hopkins University, finds that biology--in particular the hormonal influences on developing infants' brains--programs children to eventually identify as either male or female, almost regardless of social influences, at least in the case of the children he's studied.

"It's fair to say that some people in the world of psychology have held that [gender] is socially derived, learned behavior," says Reiner. "But our findings do not support that theory."

However, other researchers, such as Sheri Berenbaum, PhD, a psychologist at Pennsylvania State University, maintain that determinates of gender identity may be more complex than that.

"Genetic and hormonal factors are just two of the many influences on gender identity and gender-typical behavior--social influences are certainly very important as well," she says. "And all of these factors seem to interact throughout a child's development."

New findings

This isn't the view of Reiner and Gearhart though, who point to the findings of their study, published in the Jan. 22 issue of the New England Journal of Medicine (Vol. 350, No. 4). The study found that some infants whose brains were exposed to male hormones in utero later identified as male even though they were raised as female and underwent early-childhood operations. Reiner says that indicates that prenatal sex differentiation can at least sometimes trump social influences.

The study followed 16 genetic males with a rare disorder called cloacal exstrophy. Children with this disorder are born without penises, or with very small ones, despite having normal male hormones, normal testes and XY-chromosome pairs. Fourteen of these children underwent early sex-reassignment surgery and were raised as girls by their parents, who were instructed not to inform them of their early medical histories.

The researchers assessed the gender identities and behaviors of these children when they were anywhere from 5 to 16 years old using a battery of measures including the Bates Child Behavior and Attitude Questionnaire and the Child Game Participation Questionnaire. Researchers also asked the children whether they categorized themselves as boys or girls.

Of the 14 children raised as females, three spontaneously declared they were male at the initial assessment. At the most recent follow-up, six identified as males, while three reported unclear gender identity or would not talk with researchers. The two participants raised as males from birth continued to identify as male throughout the study.

All of the participants exhibited male-typical behavior, such as rough-and-tumble play and having many male friends.

"If you are looking at the genetic and hormonal male, [sexual identity may be] not plastic at all," says Reiner. "And it appears to be primarily influenced by biology."

Some researchers, such as Kenneth J. Zucker, PhD, a psychologist and the head of the child and adolescent gender identity clinic at Toronto's Centre for Addiction and Mental Health, applaud Reiner's study for renewing interest in the biological determinants of gender and calling into question the notion of some that gender identity is mainly socially constructed and determined by socialization.

That's not to say, however, that socialization isn't still a major or important factor, Zucker emphasizes. "The debate is still up in the air because there are other centers who have studied kids with the same diagnosis, and the rate of changeover from female to male is nowhere near what Reiner is reporting," he explains. "It must be something about their social experience that is accounting for this difference."

Contradictory evidence

Backing Zucker's belief that socialization still plays a major role--and biology is only part of the story--is research by Sheri Berenbaum, PhD, a psychologist at Pennsylvania State University, and J. Michael Bailey, PhD, a psychologist at Northwestern University.

In a study published in the March 2003 issue of the Journal of Clinical Endocrinology & Metabolism (Vol. 88, No. 3), they investigated the gender identity of genetic girls born with congenital adrenal hyperplasia (CAH). Girls with this disorder do not produce enough of the hormone cortisol, which causes their adrenal glands to produce an excess of male sex hormones. As a result, they develop in a hormonal environment that's between that of typical boys and typical girls. These girls tend to have ambiguous genitals, and like the infants with cloacal exstrophy, they generally undergo surgery to remake their bodies in the mold of typical females.

The researchers recruited 43 girls with CAH ages 3 to 18 and assessed their gender-typical behaviors and gender identities using a nine-item questionnaire. One question, for example, asks the child if she would take the opportunity to be magically turned into a boy.

In comparison with a control group of normal girls, those with CAH answered questions in a more masculine way. However, when compared with hormonally normal girls who identified as tomboys, they scored closer to typical girls. And few, says Berenbaum, actually identified as male.

"They behave in some ways more like boys, but they self-identify as girls," she explains.

According to Berenbaum, this shows that prenatal hormones, while important determinates of gendered behavior, aren't the only ones.

"Social influences are also pretty important," she says. "I think the interesting question is how biological predisposition affects our socialization experiences."

Diane Ruble, PhD, a New York University psychologist specializing in early childhood gender identity, agrees.

"In Sheri's work, the hormonal exposure has some masculinizing influence on their play behavior," says Ruble. "That may feed into difficulties that children have even if the hormonal exposure prenatally did not actually directly affect their identities as girls or boys."

For example, she says, a girl who discovers that her behavior is slightly masculine may feel more like a typical boy than girl. She may then primarily socialize with boys, leading to even more male-typical behavior.

"Obviously, gender is both a biological and social phenomenon," says Ruble. "Researchers now really need to look carefully at the unfolding of biologically driven processes in interaction with social influences during the first three years of life and beyond."

Further Reading

  • Berenbaum, S.A., & Bailey, J.M. (2003). Effects on gender identity of prenatal androgens and genital appearance: Evidence from girls with congenital adrenal hyperplasia. Journal of Clinical Endocrinology and Metabolism, 88, 1102-1106.

  • Martin, C.L., & Ruble, D.N. (in press). Children's search for gender cues: Cognitive perspectives on gender development. Current Directions in Psychological Science.

  • Martin, C.L., Ruble, D.N., & Szkrybalo, J. (2002). Cognitive theories of early gender development. Psychological Bulletin, 128(6), 903-933.

  • Reiner, W.G., & Gearhart, J.P. (2004). Discordant sexual identity in some genetic males with cloacal exstrophy assigned to female sex at birth. The New England Journal of Medicine, 350(4), 333-341.

  • Zucker, K. J. (1999). Intersexuality and gender identity differentiation. Annual Review of Sex Research, 10, 1-69