Is Gender Hard-Wired in Our Brains?

Men and women are obviously born physically different, but are our brains hard-wired to display masculine and feminine traits? Wednesday’s SciCafé event, “How the Brain Shows its Feminine Side,” at the American Museum of Natural History in New York City, explored this question.

According to event speaker Bridget Nugent, an epigenetics researcher, genetic gender is determined at conception, when parents give off X and Y chromosomes. But the composition of the male/female brain is not formed until the second trimester in the womb, when certain hormones are sent to the brain. This is the critical period, she said.

In her research with a colleague at the University of Maryland School of Medicine, Nugent injected a viral gene—almost like the common cold, she explained—into female rats days after they were born. They found that the gene modified the female rats to display masculine mating tendencies toward other female rats, suggesting that the critical period for formation of male and female characteristics is not as firm as once thought.

“Physically, these animals were females, but in their reproductive behavior, they were males,” said Nugent in a press release about the study. “It was fascinating to see this transformation.”

For her doctoral thesis, Nugent focused on how hormones create sex difference in the brain. “DNA Methylation [DNMT] is an epigenetic process that silences genes. DNMT enzymes add methyl and this usually stops a gene from being expressed,” she explained. The female brain has a higher level of DNMT during the aforementioned critical period. [Read more about the specifics in this PBS article.]

In summary, three key takeaways from Nugent’s research are:

  • Feminization of the brain is an active process. To sustain a female rat brain in development, high levels of DNMTs must be maintained.
  • The brain appears to have the circuitry for both male and female behaviors.
  • Sex differences in the brain are not as hard wired as once thought.

SciCafe is a free monthly event that takes place at the museum. Visit for upcoming events.

For more reading on sex differences in the brain, check out our 2014 Cerebrum article, “Equal ≠ The Same: Sex Differences in the Human Brain,” and its follow-up piece.

– Blayne Jeffries

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