There is a long history of seeking pseudo-scientific explanations for racist beliefs. See for example, phrenology and eugenics.
I am actually glad that you concede that "cultures" can affect learning, not merely evolution. While most people usually use that term to blame minorities for their disadvantages (i.e. culture means "their" culture), it also means that you implicitly accept that living in a (shared) culture with systematic racism and discrimination over several centuries can perhaps negatively affect skill acquisition as well.
Of course. There's rarely a single cause for anything.
But in today's world, real systematic discrimination in hiring and employment isn't likely to be the main driver at places like Google. When you're selecting for individuals several standard deviations above the mean in ability, even very slight shifts in the population mean dramatically affect the number you'll find at such a threshold. This is a touchy third-rail subject, one we'd probably do well not to discuss much, but when the alternative is constantly being told that you're racist or prejudiced, people will naturally want to fight back.
If the city police or local factory had extremely lopsided racial representation, I'd be much more inclined to believe it's due to prejudice. Any average person can do these jobs. Even if there are differences between groups, all groups would have a huge number of people around the average range.
And I'm not saying this out of some attempt to claim supremacy, justify prejudice, or advocate for eugenics. My family is from Portugal. If I had to wager, I wouldn't bet on Portuguese being at the top of the heap intellect-wise, on average. Look at who's winning the Nobel Prizes and Fields Medals--it's not people like me most of the time. Still, we should treat every person as an individual, with respect and dignity.
I am actually glad that you concede that "cultures" can affect learning, not merely evolution. While most people usually use that term to blame minorities for their disadvantages (i.e. culture means "their" culture), it also means that you implicitly accept that living in a (shared) culture with systematic racism and discrimination over several centuries can perhaps negatively affect skill acquisition as well.