As I recall, the statistics I've seen indicate that children actually exposed to direct violence against them will lower IQ, likely due to injury.

The reason I talked about paranoia is because being hypersensitive to threats is a promotion of very short term time preference. Short term time preferences don't sex-select for long-term time preferences, and short term time preferences don't incentivize IQ either. This is because anything that requires high IQ, requires a significant amount of investment in brain power, which requires other needs to have been secured first. You're making a large capital investment in intellect for it's long term benefits. If you don't feel like you can make a large capital investment in intellect because of other perceived threats, then you keep just going along with short term time preferences.