My new best friend, "rdw", kept saying in response to my demographics post that the fall in fertility rates over the last 40 years was due to abortion. Or at least, the drop for black people was due to abortion, even though the rates fell for white people as well, because black people are out-of-control reproducing machines who have three times the abortion rate. Or something.
I responded that this couldn't be the case, because fertility rates dropped precipitously before abortion was legalized. They also dropped among groups who have a strong aversion to abortion, like the Mormons, and they even dropped in countries where abortion is still illegal, like Iran. (Incidentally, this also shows what's wrong with the religion=fertility hypothesis; in spite of being 98% Muslim and a theocracy, Iran's total fertility rate is 1.82, which is less than that of America.) So while abortion may reduce fertility somewhat, it's clearly not what's been driving the rates down in general.
He didn't believe me. There's no way, he said, that there could be as many abortions as there are without causing birth rates to fall. I pointed out that women who had abortions usually did so to delay having children, not to avoid having children altogether, so there's no reason to think that abortion should lower total fertility that much. But the question still remains: to what extent, if at all, does abortion reduce fertility?
I did some poking around and found this study from the RAND corporation. I haven't scrutinized the study methodology, but RAND is a highly respected research organization and, unlike other "think tanks", it does not have an ideological affiliation. So I will tentatively accept their findings until I have a reason to doubt them. Here are the results:
We can see here that in a hypothetical example where abortion is illegal, the effect on the white fertility rate would be miniscule, a less than 5% increase. The effect on the black fertility rate would be more significant but still minor -- about a 15% increase. This supports my contention that abortion isn't a significant factor in changing fertility rates. Consider that in order to get back up to 1960 levels, the white fertility rate would have to increase by 74%, and the black fertility rate would need to increase by 118%, and you can see that abortion is not a meaningful cause of demographic change.
Nevertheless, this hasn't stopped some anti-abortion crusaders from calling abortion black genocide and likening its effects to the Klan and slavery. I'm afraid they've gotten it all wrong, and since it's surely just a misunderstanding on their part, I'm going to write to each of these groups to explain that it's a lack of conception that's been causing black birth rates to fall. If they truly care about declining black fertility, they need to start encouraging as much irresponsible sex as possible to get these conception rates back up to where they used to be. They'll be quite receptive, I'm sure.
