(Rethinking) Gender

Now, as transgender people become more visible and challenge the old boundaries, they've given voice to another debate—whether gender comes in just two flavors. "The old categories that everybody's either biologically male or female, that there are two distinct categories and there's no overlap, that's beginning to break down," says Michael Kimmel, a sociology professor at SUNY-Stony Brook. "All of those old categories seem to be more fluid." Just the terminology can get confusing. "Transsexual" is an older term that usually refers to someone who wants to use hormones or surgery to change their sex. "Transvestites," now more politely called "cross-dressers," occasionally wear clothes of the opposite sex. "Transgender" is an umbrella term that includes anyone whose gender identity or expression differs from the sex of their birth—whether they have surgery or not.

Gender identity first becomes an issue in early childhood, as any parent who's watched a toddler lunge for a truck or a doll can tell you. That's also when some kids may become aware that their bodies and brains don't quite match up. Jona Rose, a 6-year-old kindergartner in northern California, seems like a girl in nearly every way—she wears dresses, loves pink and purple, and bestowed female names on all her stuffed animals. But Jona, who was born Jonah, also has a penis. When she was 4, her mom, Pam, offered to buy Jona a dress, and she was so excited she nearly hyperventilated. She began wearing dresses every day to preschool and no one seemed to mind. It wasn't easy at first. "We wrung our hands about this every night," says her dad, Joel. But finally he and Pam decided to let their son live as a girl. They chose a private kindergarten where Jona wouldn't have to hide the fact that he was born a boy, but could comfortably dress like a girl and even use the girls' bathroom. "She has been pretty adamant from the get-go: 'I am a girl'," says Joel.

Male or female, we all start life looking pretty much the same. Genes determine whether a particular human embryo will develop as male or female. But each individual embryo is equipped to be either one—each possesses the Mullerian ducts that become the female reproductive system as well as the Wolffian ducts that become the male one. Around eight weeks of development, through a complex genetic relay race, the X and the male's Y chromosomes kick into gear, directing the structures to become testes or ovaries. (In most cases, the unneeded extra structures simply break down.) The ovaries and the testes are soon pumping out estrogen and testosterone, bathing the developing fetus in hormones. Meanwhile, the brain begins to form, complete with receptors—wired differently in men and women—that will later determine how both estrogen and testosterone are used in the body.

After birth, the changes keep coming. In many species, male newborns experience a hormone surge that may "organize" sexual and behavioral traits, says Nirao Shah, a neuroscientist at UCSF. In rats, testosterone given in the first week of life can cause female babies to behave more like males once they reach adulthood. "These changes are thought to be irreversible," says Shah. Between 1 and 5 months, male human babies also experience a hormone surge. It's still unclear exactly what effect that surge has on the human brain, but it happens just when parents are oohing and aahing over their new arrivals.

Here's where culture comes in. Studies have shown that parents treat boys and girls very differently—breast-feeding boys longer but talking more to girls. That's going on while the baby's brain is engaged in a massive growth spurt. "The brain doubles in size in the first five years after birth, and the connectivity between the cells goes up hundreds of orders of magnitude," says Anne Fausto-Sterling, a biologist and feminist at Brown University who is currently investigating whether subtle differences in parental behavior could influence gender identity in very young children. "The brain is interacting with culture from day one."

So what's different in transgender people? Scientists don't know for certain. Though their hormone levels seem to be the same as non-trans levels, some scientists speculate that their brains react differently to the hormones, just as men's differ from women's. But that could take decades of further research to prove. One 1997 study tantalizingly suggested structural differences between male, female and transsexual brains, but it has yet to be successfully replicated. Some transgender people blame the environment, citing studies that show pollutants have disrupted reproduction in frogs and other animals. But those links are so far not proved in humans. For now, transgender issues are classified as "Gender Identity Disorder" in the psychiatric manual DSM-IV. That's controversial, too—gay-rights activists spent years campaigning to have homosexuality removed from the manual.