Baboons choice for partner more than just a big backside, study

The two hikers play with a baboon at Lake Nakuru National Park. When choosing a mate, male baboons do not really care about the size of a female's backside. [Photo: file/standard]
If head-turning socialite Vera Sidika was born among our primate cousins living in Amboseli National Park, she would never have caused any stir among the males.

Scientists from the National Museums of Kenya, Institute of Primate Research, Nairobi and the Duke University, US, say among the baboons of Amboseli, much unlike our men, it takes much more than just a voluptuous backside to gain their attention.

Biologists have long thought that male baboons prefer bigger backsides as the mark of a good mother, but the new research at Amboseli suggests it isn't that simple.

In a statement, Duke University said baboons breed throughout the year, and mating occurs during times when a female's behind is swollen, a sign that she may be ready for fertilisation.

Now the study on the primates, published last Monday in the journal Animal Behaviour, revealed that the size of a female's swollen rump doesn't matter as much as previously thought.

"For 10 to 20 days each month, the tissue in a female baboon's hindquarters swells up, reaching peak size when a female is most fertile and then shrinking back to normal," said Courtney Fitzpatrick one of the researchers.

Measurements from 34 females revealed that some females swell more than others. The biggest bottom belonged to a female named Vow, whose rump swelled by 6.5 inches as she approached ovulation.

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The smallest belonged to a female named Lollipop, whose bottom only increased by four inches. The researchers recorded male courtship behaviour during the time when females were swollen. They found that big-bottomed females were no more likely to attract mates than their smaller-bottomed counterparts.

They were surprised to find that females with bigger backsides don't necessarily make better mothers, as evidenced by the fact that females with fuller fannies didn't produce more surviving infants.

"Instead of going for bigger backsides, males preferred females that were more likely to get more surviving infants," says Fitzpatrick.

This means the male is more interested with the females who will give him more children and see most of them survive than the size of the backside. The researchers indicate that for the male to accurately asses the size of the rump is no matter of scorn. From these findings the researchers suggest that baby readiness means more to males than an ample derrière. Rather than size, it seems that males calculate how long it takes for the females' periods to return after giving birth as a cue to gauge their likelihood of making a baby.

"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," Fitzpatrick said.

The study, the three authors say, disapproves earlier thoughts that like human females their counterparts among baboons compete for mates by advertising their inherited bodily assets.

The Amboseli Baboon Project, established 40 years ago, is considered to be the longest-running study of wild primates in the world.

During the period the project says it has accumulated life history information on over 1,500 animals but currently it is monitoring 300 animals.

The researchers say the work has helped them understand that young baboons who grow up without a father reach adulthood more slowly. They also say they have learnt that low ranking mothers have sons with higher levels of stress.

The question of why men may be on the look-out for a very specific kind of spine curve in sexual partners is well documented in science.

Researchers writing in the journal of Evolution and Human Behaviour in March argued that it is not about size but what your lower vertebra do with the spine curve. And that could be because women with that specific spine curve were more likely to give birth successfully, making them more attractive as partners.

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vera sidikababoonswildlifekenya wildlife serviceNational Museums of Kenya