Pretty sure that average IQ has little to do with genetics (except for actually having the genes of a human being) and everything to do with education level, health conditions, crime levels, stable government/society and so on. Specific individuals with abnormal high or low IQ might have a gift or curse passed on from their parents, sure. I'm sure that length of life, level of education, and income correlate with IQ on average and would bear out in a similar order.
If water rots the soles of your boots, what does it do to your intestines?