As a Latin American adult, I offer the counter-evidence that most adults I know can drink milk with little issue, while few are fluent in English. The mutation

As a Latin American adult, I offer the counter-evidence that most adults I know can drink milk with little issue, while few are fluent in English. The mutation that allows humans to drink milk beyond their infancy spread about 10 millennia ago, way before the Indo-European family of languages was a thing. Edit: Did a little sleuthing. I'm from Mexico, and just learned that half of the Mexicans can't digest milk. Seems like we imported the mutation from the Spanish/Portuguese since the indigenous people are the least able to digest milk. I live in Northern Mexico, and while most of Mexico is a cauldron of mixed races, the further South you go, the more pure indigenous people you can find. That's why in my social circle most people possess the lactase adaptation, but if I lived further South, less and less people would. Live and learn.