Anything your biology does it does at the cost of what else it could be doing.
Genes that could contribute to high intelligence could also contribute to mental insanity, autism, or any number of other negative things.
If there was no “cost” to a gene that unambiguously made people more intelligent - it would rapidly reach 100% penetrance in human populations.
As it is generally assumed that there is an unequal distribution of intelligence genes in human populations - it seems obvious that higher intelligence comes at a cost that would counteract the tendency for such a gene to reach 100% penetrance in human populations.
Why haven’t murderers reached 100% penetrance of the human population?
>>There IS a link between creative genius and madness - with both schizophrenia and bipolar disorder frequent in highly creative and intelligent people.<
Every highly intelligent person I have ever met was bipolar ... living in a world of continuous deep thought and high imagination while at the same time attempting to slow down enough to fit into the common world of insane laws and rules forced upon society by incompetent bureaucrats and managers who long since should have retired or been fired.
There has to be some environmental pressure which causes those people with the gene to be more successful at breeding than those without the gene. If a gene does not provide a dramatic increase in an organism's chance of breeding (or surviving to breed) then there's no reason for that gene to increase in the gene pool.
I don't see many examples of hyper-intelligence granting people increased breeding opportunities.