Her examples and arguments are compelling. She disputes many commonly-held beliefs, including ones about the very process of fertilisation. There is evidence that rather than patiently awaiting penetration, the egg engulfs the sperm, possibly selecting which sperm to merge with. Similarly, the traditional model that female primates merely tolerate intercourse with the males in their troop is discounted. Genetic tests show that about half the infants born in troops are fathered by males outside the troop, despite the efforts of the males to isolate the females from outsiders.
Female chimps have much more say in the fathers of their children than previously imagined.
She also provides evidence that primate and other mammal males have more influence on infants than previously believed. In many species, the males helping to raise, feeding and protect children which they believe to be their own. Under different circumstances, they often commit infanticide. The theme of mothers rationally reducing their losses by failing to invest in offspring with only a slight chance of success is one Hrdy discusses from many angles. Although she takes examples from a wide range of creatures, including insects, birds, and mammals of all sorts, she keeps returning to human examples.