"Do you come here often?"
Monkey business: Male chimps 'pay for sex' by grooming their mates
Last updated at 11:07am on 3rd January 2008 Daily Mail
Male macaque monkeys "pay" for sex with females by grooming them, scientists believe.
In areas where there are fewer females, males are forced to groom their partners for up to twice as long before they are able to have sex, the research found.
Sexual activity among a 50-strong group of long-tailed macaques in Kalimantan Tengah, Indonesia, increased after bouts of male-to-female grooming, according to findings published in Animal Behaviour journal and reported in New Scientist.
On average, females had sex 1.5 times an hour, but it jumped to 3.5 times an hour immediately after the female monkey was groomed by their male partner.
The females were also less likely to look elsewhere for sex after being groomed.
The monkey version of the "world's oldest profession" is also a rare example of market forces acting in nature, with the availability of females affecting the "price" of mating.
Michael Gumert of Nanyang Technological University, Singapore, said unlike examples of "reciprocal altruism" - in which one organism provides a service to another in return for getting something back at a later date - the value of sex fluctuated like any other economic commodity.
When there were several females in the area, the male monkeys would only have to do eight minutes of grooming before being able to mate.
But if there were fewer females than males around, a male would have to groom his partner for up to 16 minutes before sex, the research found.
Dr Gumert said: "When the opportunity arises, male macaque monkeys groom females to 'pay' for sex."
The macaques' behaviour is thought to be an example of a "biological market", a theory developed by Ronald Noe of the University of Strasbourg, France, and Peter Hammerstein of Humboldt University, Berlin.
Prof Noe said market forces had a strong influence on behaviour - in both animals and humans.
"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," he said.