Sexual Identity Is Not As Simple As X and Y, Scientist Says
The transgender story of Caitlyn Jenner, formerly Bruce Jenner, continues to raise discussions across America about what it means to be a man or a woman.
The simplest answer – that a woman has two X chromosomes and a man has one Y and one X chromosome – provides an incomplete picture.
What makes a fetus become a male or female is more complicated than who ends up with a Y chromosome, says Peter Schattner, a scientist and author of the book “Sex, Love and DNA: What Molecular Biology Teaches Us About Being Human” (www.peterschattner.com).
“Our sex is determined less by our chromosomes than by individual genes and the proteins that are encoded in those genes,” Schattner says. “For example, there are healthy, although infertile, men who do not have a Y chromosome. At the same time, normal women can have a Y chromosome.”
Yet even as science show us how genes and proteins make some fetuses develop the physical characteristics of a male while others have female features, understanding what makes us feel that we are male or female is still challenging.
In fact, some people, such as Jenner, have a condition called gender-identity reversal or gender dysphoria.
“They appear on the outside to be unambiguous members of one sex, while their brains tell them they belong to the opposite sex,” Schattner says.
Science is still unraveling many of the complex questions about gender, he says, but some things have become clear, such as:
• Gender-identity reversal is not the same thing as homosexuality. “Some homosexual individuals are gender-identity reversed, but most aren’t,” Schattner says. “Some individuals with gender-identity reversal are attracted primarily to the opposite sex; others are not.”
• The prevalence of gender reversal is difficult to estimate because people with gender dysphoria are frequently reluctant to speak about it. Estimates of gender-identity reversal range from 1 or 2 per 1,000 people to 1 or 2 per 10,000, with considerable variation in different societies, Schattner says. Consistently higher estimates of transgender prevalence are found in surveys made by transgender activists than those by mainstream psychology organizations, he says. But even using the most conservative estimates, about 30,000 transgender people are living in the United States and an estimated 60,000 Americans have undergone gender-change surgery over the last 60 years.
• Not that long ago, many scientists believed a person’s gender identity was largely, if not completely, determined by childhood education and upbringing. “The view was that if you are raised as a boy, you would see yourself as a boy, and if you were raised the way girls were traditionally raised, you’d develop a female self-image,” Schattner says. Now scientists are learning how genetics and prenatal biology play important roles in determining someone’s sexual identity, he says.
Although progress has been made, questions remain and efforts continue to understand the complete picture, Schattner says.
“The origins of human sexual orientation and gender identity,” he says, “remain among science’s most frustrating and challenging puzzles.”