system
Given the following post, respond as if you're commenting on Reddit:
human
Why are people from East Asia so likely to be lactose intolerant?

It seems that people from East Asian countries are massively lactose intolerant when compared to West Asians, Africans, Europeans, and so forth.  I was wondering if it's because they consume less dairy into adulthood, or if there is a genetic factor involved.
gpt
You have that backwards.

All mammals, including primates, are "likely" to be lactose intolerant in adulthood. 

People in some human groups, such as Europeans, Africans, and Indians (India, not America - Native Americans are effectively 100% lactose intolerant), are likely to retain the ability to digest lactose in adulthood.