Mating may be a natural instinct, but monkey business doesn't come free for male macaques who have to "pay" females for their affections, the AFP reported Wednesday.

According to the report, a study of the primates conducted by Michael Gumert of Nanyang Technological University in Singapore found that the male monkeys must first groom the female before she will permit sex. The males use grooming as a form of currency to buy sex from the female, the study found.

Click here to read more of the AFP report at The Raw Story.com

Left to her own desires, a female macaque mates about 1.5 times an hour, but that rate jumps to 3.5 times an hour when the male partner first provided grooming services, the study found.

The results of the study, which followed 50 long-tail macaques for 20 months in Kalimantan Tengah, Indonesia, will be published in the British journal New Scientist on Saturday, the AFP reported.