|Research Focus It takes two to tango

In most taxa, females are more likely than males to care for offspring. Why? Ever since Trivers ’ landmark work, the answer has been traced back to sexual differences in pre-mating reproductive investment (unequal gamete size or anisogamy). However, recent work shows that parental investment theory has inadvertently ignored a profoundly simple fact of life: every offspring has a mother and father. Taking this into account completely changes how we should think about sex differences in parental care. In one of the best-known evolutionary game theory models to explain sex differences in parental care [1], both males and females have the option to desert rather than care for offspring, but the benefits of desertion differ between the sexes. A deserting femal