Yes, we know, he wants a sexy large-breasted blond, she wants a brunette large-shouldered stud. Beauty may be in the eye of the beholder, but many researches have shown that it's in his/her nose, too.

Most mammals have an olfactory formation called the Jacobson organ, on the top of their mouth, where the vomer bone is located. This organ detects all the pheromones in the female's urine, which inform on her hormonal load and, based on this, the male takes action or not. I'm sure that you saw, in many documentaries, the odd grimaces made by hot lions or bison bulls at the rear part of the females' body. They are just sniffing urine with their Jacobsons, in a behavior called flehmen.

Even if the human Jacobson is not visible, many researchers say it reacts to human sweat. Maybe, that's why women are attracted by the macho man handling a pick-hammer, sweating in the sunlight. The scent of the man sweat can regulate the woman menstruation and favor fertilization. A woman's brain can detect chemicals in the man's sweat in only 3 seconds when they first date.

The woman's nose can detect also perfumes associated with male scent, like musk, in amounts below those that trigger conscious sensations. That's why perfumers put in perfumes pheromones found in nature, like musk or civet (more recently, their synthetic types).

In the scent, the female brain can find information on the man's immune system: if it's stronger than hers or complementary, she will find the man attractive and endowed with a mysterious magnetism. Swiss researchers at the University of Berna, led by Claus Wedekind, made the next test: they put 6 men to wear cotton T-shirts for two consecutive nights, in a neutral environment. The shirts were given to be sniffed and classified by 100 women. The results: the more different man's immune genes were from those of the woman (more specifically, man's histocompatability complex (MHC)), the more pleasant the woman found the man's scent. But, women using contraceptive pills showed no preference of this type.

The researchers explained this through the fact that fertile women looked for a partner that could boost the immunity of a possible child. After all, women enjoy wearing the T-shirts of their lovers. Why should this be? Not to mention that the erotic memories include the scent or perfume of the partner (including ex-partners)...

Gay men and lesbian women react as strongly to MHC-derived smells as straight people do, only that the response is to the smell of people of the same sex, not of the opposite one. The MHC matching seems not to work on women using hormonal contraception, as this imitates pregnancy, a period when women prefer the smell of similar MHCs to their own. This could be because they need the protection of their relatives now.

No wonder, now a Boston-based internet-dating site, launched in December, uses MHC information for finding you the perfect partner! However, let's not be too scientific (naïve): you will pay $1,995 and the eager possible partners will not find only about how your T-shirts smell, but also income and life history.