Everyone knows someone with impeccable "gaydar," the seemingly telepathic ability to tell whether someone is gay or straight. Research is robbing gaydar of its sixth-sense mystique, revealing that some people literally have the power to sniff out another person's sexual orientation—and that that ability is strongly rooted in biology.

When Charles Wysocki, a geneticist at the University of Pennsylvania's Monell Chemical Senses Center, asked volunteers to sniff underarm sweat from donors of a variety of genders and sexual orientations, some clear patterns began to emerge. Gay men strongly preferred the odor of other gay men, lesbians gravitated toward the smell of other lesbians, and straight women rated the odor of straight men higher than that of gay men. Each group, in short, preferred the smell of their first-choice mates, indicating a scent-based ability to assess sexual orientation. Another study confirmed that gay men and lesbians can recognize and identify the odor of others who share their sexual preference. This kind of scent-based gaydar enables gays to pinpoint potential partners instantly.

Researchers at Karolinska University in Sweden have added to Wysocki's findings, identifying a potential reason why gay men find the smell of other males so enticing. They found that androstenone, a steroid compound men secrete in their sweat, excited brain areas that control sexual behavior in gay men but left the brains of straight men unaffected. This suggests the chemical may be an integral part of the scent-driven signaling mechanism that attracts gay men to each other.

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