Easier access to contraception helps us all live longer. That's the message of two recent papers.
The mechanism here probably isn't what you're thinking. It's not just that better contraception means fewer childbirths and therefore less risk to women's health. Nor even is it that if people have fewer children they'll take more care of them. These mechanisms are important, but there's another.
Step one is in this paper - access to the contraceptive pill in the 1960s and 70s led to more people getting through university.
Unconstrained access to the pill increased female college enrollment rates by over 2 percentage points and reduced the dropout rate by over 5 percentage points....[and] led to increases in male college completion comparable in magnitude to the rise in completion among the women.
Quite simply, because women didn't need to look after unwanted babies, and men didn't need to get a job to pay for them, more people could finish university.
Step two is in this paper - more university graduates mean longer life expectancy:
Evidence from a sample of more than 200 U.S. metropolitan areas over the decade of the 1990s suggests that there are significant human capital externalities on health. After conditioning on a variety of city-specific characteristics, the findings suggest that a 5 percentage point decrease in the fraction of college graduates in the population corresponds to a 14 to 36 percent increase in the probability of death, on average.
This, he says, could be because graduates have healthier behaviour than others - they drink and smoke less - and this influences non-graduates to adopt healthier lifestyles too.
Connect these two steps, and the message is clear - better contraception means a longer life.
There are two messages here. One is that we cannot foresee the full long-run effects of technical change.
The other is that campaigners for better access to contraception, especially in what Adam Smith called barbarous societies, are more right than they know.