It's politically very hard to study the first hypothesis scientifically, and practically impossible for the second. So we don't know, and won't until society has matured to the point we can face these questions.

(I understand what little evidence we have points to maternal health/diet/wellbeing as the single biggest causal factor. Handouts of food - or simply money - to mothers in the latter part of pregnancy are the most effective intervention we know. But again, we know very little and it's very difficult to find anyone who can study these effects from a position of neutrality)