Why you can drink milk if you’re Northern European without digestive issues, but your ancestors couldn’t
This is more meant for modern Northern Europeans, where we see the highest allele frequencies for this variant.
I'm referring to this one:
https://snpedia.com/index.php/Rs4988235
We can see that it's highest in populations like the Irish and Swedes, but interestingly Jats from South Asia also have it at a pretty sizeable frequency, actually one of the higher ones in South Asians, which I assume is because of their elevated Steppe ancestry. Fulani groups have it as well which is interesting. On the other hand, it seems to be much lower in Mediterranean populations like Southern Italians, Greeks, and Sardinians.
But here's an interesting observation. When we look at the main ancestral populations of Europeans, namely WHG, EEF, and Steppe, they really didn't have much of this variant at all. From what I gathered from AGES: Ancient GEnome Selection, the frequencies were roughly:
WHG: 0.76%
EEF: 0.00%
STEPPE: 3.24%
I've talked about this before when it comes to pigmentation. We can see that the ancestral populations of Europeans were darker pigmented by looking at some of the major variants involved in skin, hair, and eye color. Then there was a pretty dramatic shift in allele frequencies, especially during the Iron Age around 3,000 years ago.
More on that here:
https://www.livescience.com/archaeology/most-ancient-europeans-had-dark-skin-eyes-and-hair-up-until-3-000-years-ago-new-research-finds
The same thing happened with lactose tolerance.
For those who aren’t aware, some of us don’t have this variant. If we drink milk or eat dairy products like cottage cheese, we don’t digest lactose very well 💩, because after childhood the body stops producing enough lactase to break it down properly.
Northern Europeans didn’t originally have high levels of lactase persistence either, but over time dairying created strong selection pressure for it. Milk, especially fermented dairy like cheese and yogurt, became more commonly used in some populations, and people who could digest lactose into adulthood had an advantage, so the trait increased over many generations. In other populations that same pressure wasn’t as strong, so lactose intolerance is still more common today.
Anyway, the point is that allele frequencies can change a lot in a relatively short evolutionary time. Traits that were rare can become common depending on diet, environment, and also things like sexual selection. We don’t stay the same, our ancestors weren’t the same, and human populations keep changing over generations, even if it doesn’t always look like it.
Posted Jun 8, 2026, 10:15 PM UTC