Scent and Sexual Selection

What makes two people attracted to one another? They answer may seem obvious: they like each other's looks, personality, etc. They are a good fit, physically, emotionally, and intellectually. Many would say two people that mesh well together have "good chemistry". You may think this is just a figure of speech, but recent studies have shown that biochemistry and evolution may play a much more significant role in how we choose our mates than we think.

The first example is of pheromones. Pheromones are chemical signals that trigger a response in other members of the same species. Pheromone communication is most well documented in insects, but some plants and vertebrates secrete pheromones as well.
When a woman is ovulating, she produces a pheromone scientists call copulin. When copulin is received by a man, his testosterone levels rise. He then secretes androstenone, a chemical that repels women who are not ovulating. Other nonrelated studies have shown that women display many subtle signs when they are most fertile that are meant to attract mates, like a higher voice pitch.

Reproductive cycles are not the only thing that influence attraction. In a recent study, women were asked to smell the T-shirts of men and rate which ones they found the most attractive. The results showed that women were more attracted to the shirts of men with a different major histocompatability complex (MHC) from them. MHC is a large gene family that plays a major role in immune systems. Humans can unconsciously perceive MHC types via olfaction, and choosing a mate with a different MHC than you will be beneficial to the survival of your offspring.
Interestingly, women who use hormonal contraception did not show the same results. Hormonal contraception tricks your body into thinking it is pregnant, so the biochemical factors at play don't have the same affect.

I learned all this on Oprah, but here are some other interesting articles:
For Gay Men, Different Scent of Attraction
Synthetic Pheromones

UPDATE: 4/10/09
Thanks for all the comments. A lot of you mentioned the use of pheromones in commercial products, and also of the controversy surrounding whether or not humans sense pheromones at all. I could not find a clear answer. To be able to sense pheromones, mammals need what's called a Vomeronasal organ, also called the Jacobson's organ, discovered in 1803. For decades scientists claimed that humans do not have a vomeronasal organ, or if we do, it is functionless. Research done by Dr. Margaret Johns in the 70s suggested that the vomeronasal organ that acted on humans was in the hypothalamus, the part of the brain that also produces hormones and regulates appetite, fear, and a variety of other behaviors. Evidence shows that humans do respond to chemical cues, with one example being women whose menstral cycles link up when they work or live together.
Scientists are currently developing synthasized pheromones that could be used for different medical uses, like to treat anxiety, or the symptoms of PMS. As for use in purfumes and colognes, most scientists remain skeptical about their effectiveness.
Another interesting note, the earliest purfumes were made with animal pheromones like musk from deer and castoreum from beavers. These ingredients were meant as preservatives and also to enhance the scent. As far as seduction goes, they may work for beavers but not humans.



Jane de Verges, Week 8
(Group B)