Steven Pinker -- How the Mind Works - Hampshire High Italian ...

464 J HOW THE MIND WORKSthe female's contribution is the limiting step on how many offspring canbe produced: at most, one offspring for each egg she creates and nurtures.Two cascades of consequences flow from this difference.First, a single male can fertilize several females, which forces othermales to go mateless. That sets up a competition among males for accessto females. A male may beat up other males to prevent them from gettingto a female, or compete for the resources necessary to mate, or court afemale to get her to choose him. Males therefore vary in reproductivesuccess. A winner can beget many offspring, a loser will beget none.Second, the reproductive success of males depends on how manyfemales they mate with, but the reproductive success of females doesnot depend on how many males they mate with. That makes femalesmore discriminating. Males woo females and mate with any femalethat lets them. Females scrutinize males and mate only with the bestones: the ones with the best genes, the ones most willing and able tofeed and protect her offspring, or the ones that the other females tendto prefer.Male competition and female choice are ubiquitous in the animalkingdom. Darwin called attention to these two spectacles, which hedubbed sexual selection, but was puzzled as to why it should be malesthat compete and females that choose rather than the other way around.The theory of parental investment solves the puzzle. The greater-investingsex chooses, the lesser-investing sex competes. Relative investment,then, is the cause of sex differences. Everything else—testosterone,estrogen, penises, vaginas, Y chromosomes, X chromosomes—is secondary.Males compete and females choose only because the slightly biggerinvestment in an egg that defines being female tends to get multipliedby the rest of the animal's reproductive habits. In a few species, thewhole animal reverses the initial difference in investment between eggand sperm, and in those cases females should compete and males shouldchoose. Sure enough, these exceptions prove the rule. In some fishes,the male broods the young in a pouch. In some birds, the male sits onthe egg and feeds the young. In those species, the females are aggressiveand try to court the males, who select partners carefully.In a typical mammal, though, the female does almost all the investing.Mammals have opted for a body plan in which the female carries thefetus inside her, nourishes it with her blood, and nurses and protects itafter it is born until the offspring has grown big enough to fend for itself.The male contributes a few seconds of copulation and a sperm cell