Can blood tests determine whether someone is gay

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Researchers using brain scans have found new evidence that biology—and not environment—is at the core of sexual orientation. Scientists at the Stockholm Brain Institute in Sweden report in the Proceedings of the National Academy of Sciences USA that gay men and straight women share similar traits—most notably in the size of their brains and the activity of the amygdala—an area of the brain tied to emotion, anxiety and aggression.

The same is true for heterosexual men and lesbians. Study author, neurologist Ivanka Savic—Berglundsays such characteristics would develop in the womb or in early infancy, meaning that psychological or environmental factors played little or no role. The problem was that there was no way to determine whether their responses were colored by learned social cues.

To get around this, Savic-Berglund focused on the structure and function of brain regions that develop during fetal development or early infancy—without using any cognitive tasks or rating systems.

Study: DNA test can predict whether you are gay

The researchers used MRIs to determine the volume and shapes of the brains of 90 volunteers—25 straight and 20 gay members of each sex. They found that the straight men and gay women had asymmetrical brains ; that is, the cerebrum the largest part of the brain, which is responsible for thought, sensory processing, movement and planning was larger on the right hemisphere of the brain than on the left.

In contrast, they found that women and gay men had symmetrical cerebrums. The team next used PET positron emission tomography scans to measure the blood flow to the amygdalathat part of the brain controlling emotion, fear and aggression. The images showed how the amygdala connects to other parts of the brain, giving them clues as to how this might influence behavior.

They scanned subjects' brains when they at rest and did not show them photos or introduce other behavior that might have been learned. They found that in gay men and women, the blood flowed to areas involved in fear and anxiety, whereas in straight men and lesbians it tended to flow to pockets linked to aggression.

But he cautions that these findings may vary in different people whose sexual orientation is not that clear-cutwhich his own research shows includes a majority of the population. Subscribe to Scientific American to learn and share the most exciting discoveries, innovations and ideas shaping our world today.

June 16, 2 min read. Brain scans provide evidence that sexual orientation is biological. Join Our Community of Science Lovers! On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. Subscription Plans Give a Gift Subscription.