This is at least one of the studies I've heard of: http://www.ncbi.nlm.nih.gov/pubmed/6872627

This debate is commonly referred to as the nature versus nurture debate:

https://www.google.com/search?q=intelligenc+nature+vs+nurtur...

It's a vigorous and deep debate. Happy reading!

Which is right up there with the abortion debate. In the vast, vast majority of actual cases, you find relatively little disagreement. Rare edge cases, however, ignite incendiary reactions from both sides.

As a pathologist and father, I'm 100% confident there are very good reasons for electing to abort in a variety of circumstances, not all related to the fetus or mother, though there is little reason to rejoice in any of them.

Similarly, I am 100% certain that human development is part genetics, and part environment. But we can't control our genetics. So I don't worry about that much. Maybe there's some fascinating biology discovered every few years, but I can learn good lessons from observing other parents every day.

Maybe that's a good way to frame the environment issue: if you really don't believe environment matters, then ask yourself, should you have kids so you have someone to take your frustrations out on?

The body of research can be found by searching "human biodiversity".