The abortion hypothesis is a different explanation, but it's not necessarily a better one. The proposed mechanism for abortion is that mothers who will give birth to future criminals are more likely to get abortions than mothers who will not give birth to future criminals, which seems vaguely plausible, but it's a more indirect effect than the known effects of lead exposure on brain development.
The lead mechanism is also easier to validate. Simply correlating the drop in crime with Roe v. Wade plus 20 years isn't enough--you also have to show some evidence which mothers and families demographically tend to produce more criminal children, and that these same mothers and families disproportionately chose abortion in greater rates after Roe v. Wade.
The proposed mechanism for abortion is that mothers who will give birth to future criminals are more likely to get abortions than mothers who will not give birth to future criminals
I don't think that's a correct explanation of their position.
Instead, children born who would have been aborted if it were legally available are more likely to be born into environments that lead to increased propensity to criminal behavior: poverty, no father figure, poor supervision, etc.
This is really one of the fundamental problems with the social sciences. So many studies in the social sciences take some spin on:
- 1) Observe correlation in sample.
- 2) Propose explanation for correlation
- 3) Take new sample.
- 4) See correlation still holds, therefore propose that explanation is the reason.
Of course the thing that should be clear in that process is that the explanation is irrelevant. The explanation could well be 'because 1+1=3.' There's an insufficient amount of attention directed towards falsification, prediction, and experimentation that's more than 'toy studies' or abstractly related. In many cases there are reasons for the lack of these processes (ethical concerns, time constraints, unavailability of an appropriate sample, etc) but those reasons do not change the fact that without these processes, the 'science' provided by the above sort of logic is not science - it's just plain old fashioned speculation in a fancy suit.
It could be both, and that's when you have to do things like look at the crime rate in countries that banned leaded gasoline but didn't legalize abortion, or vice versa.
The lead mechanism is also easier to validate. Simply correlating the drop in crime with Roe v. Wade plus 20 years isn't enough--you also have to show some evidence which mothers and families demographically tend to produce more criminal children, and that these same mothers and families disproportionately chose abortion in greater rates after Roe v. Wade.