@hebegebe my point is that, even simple traits that we understand pretty well, and which we know are very strongly heritable, have a huge environmental component. When we start talking about something as complex as human intelligence, to claim that it’s “all genetics” is ridiculous.
Though we are still have the barest of understanding of how brain function works and of the relationships between the genome and the brain, there are a few things that we do know.
We know that the rewires itself twice during childhood and adolescence, changes shape and function, and an adult brain is not merely a scaled up infant brain. It does not seem the least bit likely that the environment would have no effect on these processes and on the their outcomes.
If nothing else, PTSD, and the fact that trauma, which is about as environmental an factor as can be imagined, can affect brain structure, should tell us that a simple hereditary model of brain structure and function is invalid.
So if a short term trauma can cause parts of the brain to shrink, and to change the functioning of other parts of the brain, long after embryonic, infant and adolescent brain development are finished, how can anybody claim that the rest of the brain structure and function are even “mostly” determined by genes that one inherits from their parents, and are not affected by the environment in which one grows up?