Turns out that one of humanity's oldest professions may be even older than we thought.
In a recent study of macaque monkeys in Indonesia, researchers found that male primates "paid" for sexual access to females - and that the going rate for such access dwindled as the number of available females went up.
Researchers, who studied the monkeys for some 20 months, found that males offered their payment up-front, as a kind of pre-sex ritual. After the females were groomed by male partners, female sexual activity more than doubled, from an average of 1.5 times an hour to 3.5 times.
The study also showed that the number of minutes that males spent grooming hinged on the number of females available at the time. The better a male's odds of getting lucky, the less nit-picking time the females received.
