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Size does matter: … if the L.A. Times is to be believed. (And no, it’s not what you’re thinking.)

Each day, Domb would set out with an assistant to find baboons. Then she would sit and watch them for hours at a time, carefully noting how much attention the males paid to the females who were in the fertile phase of their cycle and had swollen rumps.

Domb also measured the size of each rump–and while she certainly wasn’t the first scientist to do so, her colleagues admire the precision she brought to bear. (“Very clever,” comments Sarah Blaffer Hrdy, emeritus professor of anthropology at UC Davis.) Instead of simply eyeballing rumps and rating them from 1 to 10 for size, Domb videotaped the rumps, similarly videotaped a meter stick, then digitally compared the two images.

Analyzing the data, Domb found that males spent more time fighting over the females with the biggest rumps. And they spent a lot of time hanging around grooming those females so other males couldn’t get near them.

And when Domb studied the detailed historical records for the 29 females studied, she found that the females with the biggest monthly swellings had matured earlier and had more offspring each year. The offspring they had were more likely to survive.

“It was really quite wonderfully surprising for us that we found such a strong correlation with so many measures of female fitness,” Domb says.

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