Dating and mating games
In a study of a mouse-like marsupial, scientists found that by sleeping around, females had a better chance of finding males with good-quality sperm and high sperm counts [video].
"So that means that females that mate with lots of males get more of their offspring sired by the good-quality males that increase the baby survival," Fisher told , referring to the mouse-like marsupials.
In a lab study, researchers found that female guppies mating with four different males gave birth to 73 percent more young than their monogamous sisters.
"The benefit for the female is quite clear, because if you have four husbands and you lay them each a clutch of eggs and they sit on it, you're doing much better than if you have one husband and you lay one clutch of eggs," Clutton-Brock said.