Is mental health and vastness of intellect a product of nature or nurture?
What about neurosis or mental weakness? How much of relative mental vigor
can be attributed to hybrid vigor or genetics? How much to a healthy,
nurturing home and social life?

I think there is a way that incest/in-breeding do have a deleterious impact
on mental and physical health, and a way that hybridization does promote
vigor. How far we can take this is definitely questionable.

Sue