Sexy sons, dutiful daughters

摘要

Was your father a dashing young man, and your mother a famous beauty? Did your parents have an estate as big as Texas or did you grow up in a hovel? Was food plentiful, or did you nearly starve? Sadly, such things do matter-and not only because of social snootiness. For in addition to that, improbable as it may seem, the answers could theoretically have a bearing on whether you are a man or a woman. The theory in question is that of sex ratios. It predicts whether an organism should have sons or daughters and is one of the most elegant and robust ideas in evolutionary biology. In its simplest form, it says that if all else is equal, the number of individuals of each sex in a population should be equal too. That is because if one sex is rare it will be sought after, and therefore more successful at reproducing. Any genetic change that causes an individual to skew its reproductive output towards the rarer sex will therefore be favoured by more grandchildren-thus spreading the new gene throughout the population.