Sex smells. An odor sways whether a man's walk is perceived as feminine by the opposite sex, whereas a similar scent does the opposite for females.

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Sex smells. An odor sways whether a man's walk is perceived as feminine by the opposite sex, whereas a similar scent does the opposite for females.

Is That a Man or a Woman? Trust Your Nose

Humans stink, and it’s wonderful. A few whiffs of a pillow in the morning can revive memories of a lover. The sweaty stench of a gym puts us in the mood to exercise. Odors define us, yet the scientific zeitgeist is that we don’t communicate through pheromones—scents that influence behavior. A new study challenges that thinking, finding that scent can change whether we think someone is masculine or feminine.

Humans carry more secretion and sweat glands in their skin than any other primate. Yet 70% of people lack a vomeronasal organ, a crescent-shaped bundle of neurons at the base of each nostril that allows a variety of species—from reptiles to nonprimate mammals—to pick up on pheromones. (If you’ve ever seen your cat huff something, he’s using this organ.) Still, scientists have continued to hunt for examples of pheromones that humans might sense.

Two strong candidates are androstadienone (andro) and estratetraenol (estra). Men secrete andro in their sweat and semen, while estra is primarily found in female urine. Researchers have found hints that both trigger arousal—by improving moods and switching on the brain’s “urge” center, the hypothalamus—in the opposite sex. Yet to be true pheromones, these chemicals must shape how people view different genders.

That’s exactly what they do, researchers from the Chinese Academy of Sciences in Beijing report online today in Current Biology. The team split men and women into groups of 24 and then had them watch virtual simulations of a human figure walking (see video). The head, pelvis, and major joints in each figure were replaced with moving dots. Subjects in prior studies had ranked the videos as being feminine or masculine. For instance, watch the figure on the far left, which was gauged as having a quintessential female strut. Notice a distinctive swagger in the “hip” dots and how they contrast with the flat gait of the “male” prototype all the way to the right.

An unbiased walk features in the middle frame, but when the subjects inhaled andro or estra, they judged the walk as either more masculine or more feminine. The results depended on the viewer’s sexuality. Heterosexual women and gay men perceived the gender-neutral stride as more masculine after smelling andro, whereas estra had no effect on them. In contrast, smelling estra biased heterosexual males, but not females, toward perceiving the walkers as more feminine, says study leader and behavioral psychologist Wen Zhou. Gender judgments of the simulated figures shifted on average by 8% for heterosexual men and women as well as gay men. Due to difficulties with recruitment, bisexual and homosexual women were pooled together. Neither andro nor estra swayed their gender perceptions, but that may reflect the mixed orientations in this group. 

The possibility that subconscious networks in the brain sense pheromones and alter our behavior is very interesting but challenging to prove, says Ivanka Savic-Berglund, a neurologist at the Karolinska Institute in Stockholm who was not involved with the work. She cautions that this is just one study that must be reproduced before a final verdict is made, but it “puts a question mark on the view that pheromones don’t affect humans.”

(Video credit: Zhou W et al., Current Biology [2014])

Posted in Biology, Brain & Behavior