It's intelligence even considered to be something that is directly heritable these days? I thought that too many genes and possible gene combinations were involved.
I am not aware of the latest studies, but older research indicates that intelligence is highly inheritable.
An anecdotal observation: When our son was 6 weeks old, we took him to a pediatrician, who had been practicing for almost 40 years had treated thousands of kids over his career (he has since retired). We knew him well because he had also been the pediatrician for our daughter, who was 3 years old at the time. After the 6-weeks exam, the pediatrician told us jokingly "don't bother saving money for college with this one, he will get scholarships for everything". He said this because our son was unusually attentive relative to the many other patients he had.
Since then DS, has been tested and found to be PG. Obviously at six weeks there was no unusual nurturing for DS compared to DD, so the difference was really nature.
