We regard prostitution as extremely immoral and as degrading the human beings. But it seems this is much older than we would believe. In our evolutionary history, we could trace this to more than 15 million years ago. A new research reported in New Scientists reveals that even in monkeys males pay for sex. Only that, as macaques do not have money, their currency is grooming.

The 20-month research was carried on by Michael Gumert of Nanyang Technological University in Singapore and was made in a group of 50 long-tailed macaques (Macaca fascicularis) in Kalimantan Tengah, Indonesia.

A mature female macaque had on average about 1.5 sexual contacts per hour. But her sexual activity boosted to 3.5 times per hour as soon as she was groomed. But it was not exactly the grooming what made her feel sexier: the advantage of her increased sexual charm was taken exactly by the hard working groomer.

But if you thought that this followed the mere rule of reciprocity, you're wrong. The transaction followed strict market rules of demand and offer. If there were more females in the zone, sex got incredibly cheap: a stud had to pick and eat female's lice and dandruff just for just eight minutes. But if there was just one "prostitute" on the corner, the poor sex desired monkey hunk had to sweat for up to 16 minutes before getting some seconds of pleasure.

These observations strongly enhance the economical theory that biological market forces are behind social behavior.
"When the opportunity arises, male macaque monkeys groom females to 'pay' for sex," Gumert told New Scientist.

"There is a very well-known mix of economic and mating markets in the human species itself. There are many examples of rich old men getting young attractive ladies." said Ronald Noe of France's University of Strasbourg.