Ron Guhname (not his real name), The Inductivist, used data from the General Social Survey to look at the question of whether the legalization of abortion in America caused a change in selective pressures for intelligence. Using the GSS Wordsum test as a rough measure of intelligence Ron finds that abortion did not appear to change the selective pressures for higher or lower intelligence. The selective pressures for lower intelligence continued unchanged.
The first year of the General Social Survey was 1972. I looked at white women ages 50 and over for all surveys conducted in the 70s. The mean number of kids for dull women (Wordsum 0-4) was 3.02. It was 2.22 for smart women (Wordsum 8-10). That's a ratio of 1.36. Looking at this decade, I calculated means for white women ages 45-59. For the unintelligent group, the mean number of kids is 2.38, and it's 1.76 for the bright group. That's a ratio of 1.35.
There is no difference between the two periods. The higher fertility of dull women seen prior to 1970 continues to the same degree today.
My guess is that women use the knowledge that they can get an abortion to become more lax about use of birth control and to enable more spontaneous beginnings of affairs. Abortion might still have caused changes in selective pressures because the women who are willing to go thru with an abortion might differ in some aspect of personality as compared to women who won't.
If you are curious about modern era selective pressures for intelligence see this report from an Australian twins study. For a book length treatment of selective pressures on humans see The 10,000 Year Explosion: How Civilization Accelerated Human Evolution by Gregory Cochran and Henry Harpending.
By Randall Parker at 2009 November 30 09:55 AM Brain EvolutionI can't seem to find the source right now, but I remember reading about a study done in Africa about paternity vs. poverty. Basically the poorer a woman is, the less likely her husband is to be the father of her children. My guess is that this would have a strong selective pressure toward higher intelligence.
Click the SDA interface and mouse over analysis to run a regression. Let's replicate the association our intrepid blogger found: dependent CHILDS, independent WORDSUM(d: 0-4), weight COMPWT, filter SEX(2), AGE(50-99), and both YEAR(1970-1979) and YEAR(2000-2009). You get a positive, pretty stable coefficients and an r-squared close to zero.
An effect that explains close to zero population variation doesn't strike me as likely to affect evolution.
I am well aware of the limits of such curvefitting. Still, I would go back to the drawing board.
Oh, the opening 10 minutes or so of Idiocracy. Watch it and behold our future.