Male baboons do not prefer big butts when selecting mates, a new study reveals. Female baboons are marked with distinctive bright red behinds.

Biologists previously believed that males of the species associated larger posteriors with mates that would be better mothers.

The posteriors of female baboons swell in size between 10 and 20 days each month, reaching a maximum size when the animal is most fertile. It is during this time when mating takes place, which suggested to earlier researchers that the size of a female's backside attracted males of her species.

Baboons in southern Kenya were studied in the wild by researchers attempting to ascertain how the size of a female's backside affects the attraction males have toward potential mates.

Duke University researchers utilized a camera technique usually used to measure the size of elephants and bison from a distance to record the size of baboon butts. A caliper was attached to a telephoto lens, and a mathematical formula revealed the distance to the animals being observed. By counting the number of pixels in the digital images, investigators were able to determine the size of the swollen backsides. Each of the female baboons examined showed different amounts of swelling, from 4 inches to 6.5 inches.

Investigators compared the size of the posteriors during ovulation to records of bearing offspring, correcting the data for social ranking and age of the animals. They found that instead of being attracted to females with larger swells, the males chose to mate with those females who had ovulated a greater number of times since they last produced offspring. Baboons, like human females, are more likely to get pregnant following childbirth only after they finish weaning their young.

"It's almost as if the males are counting. Our study suggests that, at least in part, males follow a rule along the lines of 'later is better' rather than 'bigger is better,' " Courtney Fitzpatrick of Duke University said.

Baboons are a genus of Old World monkeys, which include five species. Adult males can grow to be more than two feet tall and weigh more than 55 pounds. The animals can live as long as 30 years in the wild.

The investigation also revealed that females with larger posteriors during ovulation were no more likely than other animals to produce more infants that survived their first years.

Future research will examine if female baboons become more interested in mating after several monthly cycles following birth. One of the questions that could be answered by this follow-up study will examine if such behavior leads to higher survival rates for the offspring of baboons.

Study of the size of female baboon posteriors and how it affects mate selection was published in the journal Animal Behavior.

Photo: Diana Robinson | Flickr

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