Everyone knows what it's like to be powerfully affected by a partner's smell—witness men who bury their noses in their wives' hair for example. And this isn’t some cliché, it really has a scientific foundation:
Claus Wedekind, a biologist at the University of Lausanne in Switzerland, made in 1995 an experiment called ‘The Sweaty T-Shirt Study’. This study consisted in giving to 44 men new T-shirts and instructing them to wear the shirts for two straight nights. To ensure that the sweat collecting on the shirts would remain "odor-neutral", the men were provided with scent-free products, and instructed not to drink alcohol, put on perfume, or anything that could change their natural smell.
After the men were allowed to change, his shirts where put in boxes and displayed to 49 women, that sniffed the shirts and specified which odors they found most attractive. Impressively, the women preferred the smell of T-shirts worn by men who were immunologically dissimilar to them... Although, this makes perfect sense from a biological point of view. With more immune genes present, the kids created from that union are buffered against a wider variety of pathogens and toxins.
But what if we fail and wind up with a mate whose inmunologic profile is too similar to our own? The possibilities of failing in choosing a partner were explored by geneticist Carol Ober with a closed society that consisted of some 40000 members: even if women had to choose within this imposed limit, they managed to find partners who were immunologically-distinct from them most of the time. The consequences of having two similar immunological genes? The couple suffered higher rates of miscarriage and experienced more difficulty conceiving.
Again with Wedekind’s study, women generally prefer the smell of men whose genes complements are different from theirs. But this study revealed one notable exception to this rule: women taking the birth-control pill. When the pill users among his subjects sniffed the array of pre-worn T-shirts, they preferred the scent of men whose profiles were similar to theirs—the opposite of their pill-free counterparts. We all know the pill prevents the ovaries from releasing an egg, fooling the body into thinking it's pregnant, and since pregnancy is such a delicate state, it seems to activate a preference for men whose genes are similar to the ones we have and likely serve as protectors. So, summarizing, the pill subverts a woman's ability to sniff out a compatible mate by causing her to misinterpret the scent messages she receives.
The pill isn't the only way we might confound sexual chemistry. Every day, far more people may be subverting their quest for love with soap and bottled fragrances... So next time you want to get a partner, get a good sniff at him without fragrance nor consuming birth-pills, even if he is half fish like our little mermaid.