Male macaque monkeys 'pay' for sex with females by grooming them, a new research has found. The availability of females even affects the 'price'.Where there are fewer females, males must groom their partners for up to twice as long before they are able to have sex, the research found.
The male use grooming as a form of currency to buy sex from the female, the study conducted by Michael Gumert of Nanyang Technological University, Singapore, found.
Sexual activity among a 50-strong group of long-tailed macaques in Kalimantan Tengah, Indonesia, increased after bouts of male-to-female groom, according to findings published in Animal Behaviour Journal and reported in New Scientist.
On average, females had sex 1.5 times an hour. This increased to 3.5 times an hour immediately after the female was groomed by the male.
Gumert 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.
When there were several females in the area, the male monkeys would have to do only eight minutes of grooming before being able to mate. If there were fewer females than males around, a male would have to groom its partner for up to 16 minutes before sex, the research found.
The macques' behaviour is an example of a 'biological market', a theory developed by Ronald Noe of Strasbourg University, France and Peter Hammerstein of Humboldt University, Berlin.
"There is a very well-known mix of economic and mating markets in the human species. There are many examples of rich old men getting young attractive ladies," Prof Noe said.
