The economic school says that macroeconomic changes in American life have made having babies less important. As we moved from agriculture to industry, from rural life to urban life, children became both less helpful and more expensive. What's more, the advent of Social Security and then Medicare inserted the government into family life by giving the state responsibilities for taking of the elderly that children once bore.
What the entitlement state meant was that for the first time in history, people didn't need children to care for them in their old age. The government would do it. Socializing this cost created a market distortion. Children are expensive to raise and everybody gets the government's geezer goodies, whether they pay for the cost of creating new taxpayers or not. So only the suckers have kids.The idea that people have children in order to be cared for in old age is largely nonsense. Social Security was put in place partly to get older people out of the labor market in the Depression but very importantly to deal with the fact that the poverty rate was very high among the elderly--children were not taking care of their parents, no matter what Last may believe was going on back then. Most people understand that saving for your own old age is a lot less expensive than raising a child. At the same time, it is almost certainly the case that economic development and urbanization in this country led to a steep rise in the opportunity costs of children, leading young people to seek ways to gain more control over their reproduction. This latter set of issues is what Last refers to as "cultural explanations."
What happened beginning in 1970 was a massive change in American culture. Just to tick off a few of the most obvious changes: abortion, contraception, marriage, divorce, and religious practice. Each of these subjects underwent titanic shifts beginning in or about 1970. And as our relationship to them changed, so did our behavior with regards to family life.It is my view that Last has this backwards. It was not that culture changed and then family behavior changed. Rather, the very forces that have led to decades of fertility decline in the US have created the demand for greater control over one's life--including choosing the number of children, when to get married, and when not to be married. Most people want neither the government nor the church telling them what to do in these matters.