[lumberjack]

You are confusing things.

First and foremost you don't need evidence to look for evidence. A hypothesis is enough.

Secondly, there is evidence that IQ is at least in part genetic. There is no other way to explain geniuses, child prodigies, and mentally retarded individuals whose environments vary greatly.

[Evbn]

Sure there is: chemical exposure balance or random variation in the uterine or infant environment.

Fetal alcohol syndrome reliably retards kids, and it isn't genetically inherited. Hypothetically, maybe something like adderall works in utero with lifelong effects.

Also, hypothesis formation should be motivated by data, or else you are wasting time searching through an exponential space with 0 probability of finding a correct one.