As I understand it, birth defects are like 99.999% of the time unhelpful. But that 0.0001% of the time the genetic freak is a huge advantage and that gets passed down in the gene pool and thus, over many many generations, evolution.
Alcohol, which is known to increase birth defects, should increase the speed at which that happens. Right? Like playing the lottery with more tickets.
Fetal alcohol syndrome has to have a huge negative impact on population survivability. I have a hard time believing that even that one one-in-a-million genetic freak superman is able to offset that. Seems more likely that if anything, the general benefits of alcohol consumption (e.g. incentive to settle down into agrarian communities, increased social cohesion) outweight the negative health impacts.