[hntrader]

You strongly believe this based on what?

Being "99.9 percent identical" doesn't necessarily preclude substantial genetic variation in intelligence just like it doesn't preclude such variation in height or skin tone.

https://en.m.wikipedia.org/wiki/Heritability_of_IQ

[stephc_int13]

Heritability of traits is not always directly genetic.

[hntrader]

Correct.

I was asking what the basis is for your confidence that it positively isn't substantially genetic.

We know that intelligence is highly heritable, which leaves a few possible explanations, genetics being one of them (along with prenatal nutrition, prenatal lead exposure, etc).

If you're going to claim that genetics is only a small part of the reason that it's heritable, then that has its own burden of proof that needs to be met.