Researchers from the Chinese Academy of Science analyzed a group of 96 non-smokers: 50% men and 50% women. Half of each gender group self-identified as straight; the other half identified as gay. They were asked to watch a series of abstract animations of a gender-neutral human taking a walk. While watching, the subjects were exposed to either androstadienone (a steroid found naturally in semen and male armpit sweat), estratetraenol (found in women's urine and sweat), or a control solution. All of the solutions were scented like cloves, so the subjects didn't know which compound they were smelling. The scientists then asked them to assign a gender to the figures in the animation they were watching.
Both the straight men and the gay women were more likely to view the figure as a "woman" when exposed to estratetraenol, while the androstadienone had no effect. This meant that their hypothalamus, the part of the brain that interacts with hormones and senses, was activated by the female steroid compound — but not the male version. The opposite was true for the gay men and straight women.
While the suggestion that we have an innate way of sensing gender is interesting in and of itself, this finding's implications about our understanding of sexuality are arguably more significant. Why? Each subject's sensory system and brain responded subconsciously in a controlled setting based not on his or her own gender, but on the gender he or she finds the most attractive. This fact could be used as evidence for the assertion that sexuality is an innate, biological phenomenon — rather than something we acquire from our environments.
Of course, this study leaves many questions unanswered: How, for instance, do pheromones function with bisexual, pansexual, fluid, or other queer people? With trans* individuals? Clearly, more research needs to be done. Still, this study could represent a significant step forward in how we understand whom we're attracted to, and why.