An interesting area of relatively new research has found connections in gene selection and bio-chemical signals of fertility. Frequently, especially in insects, chemical signals are used to generate sexual interest and to locate potential mates. These signals, known as pheromones, are hormones produced in the skin are used to influence behavior in others. In humans, research has led us to believe that these signals are received and translated in the vomeronasal system, located alongside the nasal septum. Interestingly, the most powerful scents are the ones that most of us can’t consciously detect. Both men and women give off pheromones called androstenes, but men emit more of them. Women secrete lipids known as copulins in their vaginas. Both are used as powerful communication channels that humans are obliviously to. When women are exposed to androstenes, they feel better and find that people look better to them. When androstenes were applied to chairs in a theater and a dentist’s office, women chose those seats, while men rejected them. Astrid Jutte, a researcher who worked at the Ludwig Boltzmann Institute for Urban Ethnology, in Vienna, exposed men to synthetic copulins and found that it increased the men’s testosterone levels by 50 percent. The test subjects also rated women’s faces and voices as more attractive after the men had smelled copulins, even though they either could not detect the smell or didn’t find it pleasant. Since a woman’s sense of smell is also most acute during ovulation, men and women are biologically tuned to read each other by smell alone in such a way as to increase the chances that they’ll reproduce. (Geary et al., 2004).
There are powerful and complex messages encoded into those smells; which are produced by our immune systems. Essentially we are sampling each other’s genes when we take in copulins and androstenes, particularly the genes of the so-called major histocompatibility complex (MHC). MHC genes are the ones that detect foreign organisms, like bacteria. This allows us to tell by smell alone how closely someone is related to us. Researchers have shown that people choose mates whose MHC is least like their own. A Swiss researcher gave women T-shirts that had been slept in by men and asked them if they liked the smell. The women preferred the ones from men who were genetically different, and thought the others smelled like their brothers or fathers.
Researchers found that fetal loss increased significantly when parents shared all the genes of the HLA system, or just genes in the HLA-B region. When the time came for these males to choose mates, they avoided females whose MHC genes were similar to their foster mothers’, even when that meant winding up in the position of mating with a female whose MHC genes were similar to their own. These results suggested that animals might somehow be able to detect prospective mates whose MHC genes are more or less similar to their own, and then to choose mates accordingly. They may have evolved such an ability because of MHC’s importance in the immune system, or simply because MHC sensibility is a way to distinguish relatives from nonrelatives, thus avoiding inbreeding. If odor does provide information about the immune system, it makes evolutionary sense for women to pay special attention to smell. They have much to lose if they mate with an inappropriate male and give birth to a baby with a reduced ability to fight off disease.