PROBLEM: A Gallup poll last week said that 47 percent of people in the U.S. understand sexual orientation to be congenital. In 1978, that number was only 13 percent. Here's how Americans have tracked over recent decades in response to "In your view, is being gay or lesbian something a person is born with, or due to factors such as upbringing and environment?"
As people's understanding changes, science is working to clarify what "born with" means. In the late 1990s, conversation around a "gay gene" was very controversial. We won't likely trace human sexual orientation to a single gene, but research has made it apparent that sexuality can be influenced by manipulating genes, hormones, and neurotransmitters. Altering balances of testosterone and estrogen has been shown to affect sexuality, and imbalances of the neurotransmitter serotonin can make us hypersexual. In mice, serotonin has been tied to sexual preference -- mice bred without certain neurons have shown "no sexual preference." But scientists have never "reversed" any species' sexual orientation by messing with their genes.
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METHODOLOGY: Researchers led by Shasha Zhang at Peking University in Beijing and reviewed by Dr. Catherine Dulac at Harvard bred certain female mice that lacked either serotonin or certain neurons that release serotonin in parts of their brains. They then compared their behaviors to the typical non-mutant mice.
RESULTS: Those mice with the mutations showed preferences for sniffing the head and genital areas of other female mice, as well as "try[ing] to grasp ... females by the waist before mounting on their back. ... Females displayed strong mounting preference toward the females, mounted female targets with shorter latency, higher frequency, and longer duration." Here are two examples of what scientific findings about mice defiling each other looks like in a prestigious academic journal:
IMPLICATIONS: "Mutant females lacking serotonergic neurons" showed preferences for females over males. Zhang and company concluded that not having certain neurons that release serotonin "cause[d] a reversal of sexual preference, revealing a role for [serotonin] in regulating sexual preference."
Use of the word mutant could seem unfortunate, but it's just a trade term used in every article about genetics ever, describing changes relative to a given starting point.
For now this is just an interesting experiment that tells us serotonin plays a role in sexual orientation. Understanding the biochemistry of human sexuality and the ethical discussions that will come with investigating and manipulating genes that potentially influence sexual orientation still seem a long but interesting way off.
The full study, "Serotonin signaling in the brain of adult female mice is required for sexual preference" is published in the journal Proceedings of the National Academy of Sciences.
