A recent paper in Behavioral Ecology suggests that human males do not solely use visual cues to determine if a female within their radar is "sexy." Okay, so this may fall into the range of "Well, duh!" but then again, the implied question of whether or not particular deviances (i.e. panty sniffing) are learned or just an exaggeration of something innate should cause certain people pause--because what exactly is normal?
Instead of going into philosophical discussions of normality that I am neither qualified nor particularly interested in rambling about, I will say a little more about the study. Kuukasjarvi et al. wanted to challenge the assumption that men are absolutely clueless about when a woman is fertile during her mentrual cycle. In many primate species, females advertise their stage in ovulation by visual cues. For humans, this is concealed, leading to the hypothesis that if this was an adaptation in the female, then perhaps males counter-adapted by evolving ways to detect olfactory cues. In other words, ancient man developed the ability to sniff out the women who were at their peak fertility phase.
In the experiment, the researchers had women in varying phases of their menstrual cycle as well as about half that were on oral contraceptives and half that were not, wear a T-shirt for two consecutive nights. Then the researchers had both men and women rate the T-shirts' odors for attractiveness. After putting the data through the statistical wringer, the study indicated that male raters preferred the odors of women near ovulatory phase in their mentrual cycles. This only applied to the T-shirts where the women were not on contraceptives. Apparently the pill affects hormone levels and eliminates the "attractive odors."
So what are these odors and what exactly do they do? This study doesn't address that question specifically, but there are several possibilities. Odors from the human body can be affected by hormone levels. Steroid hormones are secreted through sweat glands. When these steroid hormones come in contact with bacteria on the skin, the bacteria convert them into odorous compounds. Another possibility is that the T-shirt sniffers weren't rating the odors per se, instead they could have been detecting pheromones via the vomeronasal organ (VNO). (Then, there are other people who argue that the VNO is vestigial and probably as useless as a sixth finger.) A third possibility is that body odor is affected by a person's major histocompatibility complex (MHC) type. MHC is involved in immunity and some hypothesize that people seek out mates with a different MHC type to prevent inbreeding.
Of course, this doesn't say anything about some women's penchant for overwhelming amounts of perfume.
Other Smelly T-shirt Studies:
Singh and Bronstad, 2001. (ABCNEWS summary)
Wedekind et al., 1995; Wedekind and Furi, 1997. (New Scientist overview)
(Cross-posted at Syaffolee.)