 No Need for Pheromones
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June 17, 2003 — Forget about using those expensive sprays to try and attract the opposite sex — humans don't have the ability to detect pheromones, and American research concludes it is due to our color vision.
The research, undertaken by Assistant Professor Jianzhi Zhang from the University of Michigan, involved a comparison of the genes of primates that can see color and those that can't. It seems that males developing color vision negated the need for pheromones to attract mates.
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Pheromones are water-soluble chemicals released by an individual as a signal to others of the same species. They are used for social and reproductive behavior and in land-based animals they are mainly sensed by an organ called the vomeronasal organ (VNO). But humans and other primates only have remnant VNOs, so they have no or very little ability to detect pheromones.
Instead of using a chemical signal, Old World monkeys and hominids use visual signals such as sexual swelling to indicate sexual readiness. They can do this because they have color vision, which they developed when they split with the New World monkeys about 23 million years ago.
While female New World monkeys (tamarins, saki, squirrel, owl and spider monkeys) have full color vision, the males don’t because the color vision gene sits on the X chromosome. But their Old World cousins (humans, chimpanzees, gorillas, orangutans, gibbons, baboons and guerezas) have two copies of the gene and both males and females can see in color.
"Color vision made pheromones unnecessary," said Zhang. Once males have full color vision, they are able to sense the subtle color changes of female sexual skins. Females of many Old World monkeys and hominids are known to develop a prominent reddening and swelling of their sexual skin surrounding the perineum around the time of ovulation. In contrast New World monkeys do not have true sexual skin.
The researchers used two genes in mice whose only role is to transmit pheromones and tried to establish the activity of those genes in primates. They found that although humans and some apes still carry genes that should create pheromone receptors in our noses, they have mutated to the point that they are merely pseudogenes, and don't function any more.
The research is published in Tuesday's issue of the journal Proceedings of the National Academy of Sciences.
Visual signalling is more effective at a distance than pheromones because it is very clear which individual is sexually swelling, whilst pheromones can drift around in the wind before reaching their intended recipient.
Humans do respond to some pheromonal signals. The well documented cases of women living together who synchronizing their menstrual cycles is due to pheromones from one woman influencing the hormones of the other women in the household.
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