A female baboon's backside will swell as she ovulates, so it follows that her suitors will take it as a cue of her fertility. And they do: The swelling brings all the baboons to the yard, as it were. Some females have more swelling than others, resulting in a bigger rear on display. But surprisingly, these larger ladies didn't get any more attention from the men.
It seems that the male baboons knew better: When the observations of swelling were compared with long-term data on offspring, the researchers found that more swelling during ovulation didn't correlate with more living children.