Human pheromones are a hot topic in research. They are odourless chemicals detected by an organ in the nose. Some scientists believe they could be the key to choosing a suitable lover.
Pheromones are already well understood in other mammals, especially rodents. These animals possess something called a 'vomeronasal organ' (or VNO) inside their noses. They use it to detect pheromones in the urine of other rats and use this extra sense to understand social relationships, identify the sex of fellow rats and find a mate.
In 1985, researchers at the University of Colorado found evidence that this organ also exists in most adult humans. So humans could also respond to pheromones.
Rats have different pheromones in their urine, depending on the make-up of their immune system. When rats choose a mate, they must avoid partners with an immune system too similar to their own, so that their babies can fight off a wider range of infections. As well as lurking in urine, pheromones are also found in sweat.
Love is...a sweaty T-shirt competition
Shirts hanging on a washing line
In 1995, Claus Wedekind of the University of Bern in Switzerland, asked a group of women to smell some unwashed T-shirts worn by different men. What he discovered was that women consistently preferred the smell of men whose immune systems were different from their own. This parallels what happens with rodents, who check-out how resistant their partners are to disease by sniffing their pheromones. So it seems we are also at the mercy of our lover's pheromones, just like rats.
At the University of Chicago, Dr Martha McClintock has shown in her own sweaty T-shirt study that what women want most is a man who smells similar to her father. Scientists suggest that a woman being attracted to her father's genes makes sense. A man with these genes would be similar enough that her offspring would get a tried and tested immune system. On the other hand, he would be different enough to ensure a wide range of genes for immunity. There seems to be a drive to reach a balance between reckless out-breeding and dangerous inbreeding.