Male and Female Behavior Deconstructed

Hormones shape our bodies, make us fertile, excite our most basic urges, and as scientists have known for years, they govern the behaviors that separate men from women. But how?

Now a team of scientists at the University of California, San Francisco (UCSF) has uncovered many genes influenced by the male and female sex hormones testosterone and estrogen that, in turn, govern several specific types of male and female behaviors in mice.

The UCSF team selectively turned many of these genes off one by one and found they could manipulate individual behaviors in the mice, like their sex drive, desire to pick fights, or willingness to spend extra time caring for their young.

"It's as if you can deconstruct a social behavior into genetic components," said Nirao Shah, MD, PhD, an associate professor in the Department of Anatomy at UCSF who led the research, which is published in the 2/3/12 issue of the journal Cell. "Each gene regulates a few components of a behavior without affecting other aspects of male and female behavior.

In addition to illuminating the role of genes in male and female behavior, Shah said, the results also have greater implications: If male and female behaviors can be broken down into individual component parts, what other complex behaviors could similarly be deconstructed?

Identifying how genetic differences in our brains account for the differences in our behavior may also be a starting point for understanding how to better address human mental illness and neurodegenerative conditions in which such gender differences exist. For example, autism is four times more common in males than in females.

"Some of the genes we have identified in our study have indeed been implicated in various human disorders that are found in sex-skewed ratios," said Shah. "We won't immediately find all the answers to these disorders based on this research alone, but in the future, it might indeed help to identify more informed ways of treating such conditions."

Hormones, Sex, and Society

Scientists have known for years that hormones exert a profound control over male and female biology. They influence whether an embryo develops into a male or female fetus. They kick in during puberty and promote gender-specific characteristics, such as facial hair in men and breasts in women. They also stimulate the production of male sperm and female ova.

These actions have led to the widespread use of hormones in mainstream and fringe medicine for years. A major part of sexual reassignment procedures involves the long-term administration of hormones like estrogen or testosterone. Athletes seeking a competitive edge and middle-aged men seeking to prolong the vigor of youth sometimes use testosterone—often inducing aggressive behavior in the process.

While the connection between sex hormones and behavior has been known for years, scientists have only recently made significant headway in demonstrating how profoundly one affects the other by altering the levels of male and female hormones in laboratory animals.