People usually think they can tell a person's gender based on how he or she looks, but humans actually make subconscious judgments based on how a person smells, new research suggests.
In the study, when men or women caught a whiff of chemicals produced by members of the opposite sex, they perceived movements as being more feminine or masculine, scientists added. The results depended on both biological sex and sexual orientation, researchers said.
"[The findings] show that the nose can sniff out gender from body secretions even when we don't think we smell anything on the conscious level," study leader Wen Zhou, of the Chinese Academy of Sciences, said in a statement. [7 Ways Animals Are Like Humans]
The results of the study support the argument for the existence of human sex pheromones, or chemical signals secreted by the body that influence social behavior in others, Zhou said.
Many animals communicate using pheromones, but evidence of human pheromones has been inconclusive. Studies suggest that androstadienone, a chemical present in men's semen and armpits, can improve the mood of women who smell it. Likewise, estratetraenol, a chemical found in women's urine, has been found to have the same effect on men.
In this study, men and women volunteers watched moving dot figures, called point-light walkers, marching in place on a screen. Each walker consisted of 15 dots representing the 12 major body joints, plus the pelvis, thorax (chest area) and head.
The volunteers were exposed to androstadienone, estratetraenol or a neutral solution serving as a control, and had to judge whether the dot walkers were masculine or feminine. All of the scents smelled like cloves, to prevent any conscious recognition.
Smelling androstadienone made heterosexual women, but not men, perceive the walkers as more masculine than normal, the researchers found. Similarly, smelling estratetraenol made heterosexual men, but not women, perceive the walkers as more feminine.
Smelling one chemical signal or the other produced about an 8 percent change in gender perception — a very significant effect, Zhou said.
What's more, gay men responded to androstadienone the same way heterosexual females did. Bisexual and lesbian women had a response that was in between the response of heterosexual men and heterosexual women.
The findings provide the first direct evidence that chemicals produced by the human body can subconsciously communicate gender information based on sex and sexual orientation, the researchers said.
The new research is detailed today (May 1) in the journal Current Biology.