 In a classic early work of cultural evolution, Cavalli-Sforza and Feldman (1981) ask (among other things) how we can explain declining birth rates among Italian women in the nineteenth century. These women went from having around five children on average to having only two. It would be extremely implausible to argue that this occurred as result of natural selection (Sober 1991, 482). It would be implausible, for example, to argue that the fitness of women with smaller families was greater than the fitness of women with larger families. True enough, an individual’s long-term fitness (measured in terms of numbers of grandchildren, or great-grandchildren) may sometimes be augmented by having a few strong offspring rather than lots of weak ones (Lack 1954). But surely Italian women could have raised more than two children to be healthy adults. Cavalli-Sforza and Feldman instead argue that the practice of having fewer children spread through Italy because women acquired the trait both from peers and from individuals from their mother’s generation, through modes of cultural transmission. Forms of oblique transmission are required to explain this transition, because if cultural transmission were always vertical, then the trait of having greater numbers of offspring would be maintained in the population by natural selection, albeit selection acting via cultural inheritance.