I’m tolerant of a lot of stuff, gays, Republicans, Keanu Reeves; and there are a few things of which I am not tolerant: ignorance, racism, bigotry, and milk. I cannot help milk, though. My lactose intolerance is genetically coded into me. My ancestors decided some thousands of years ago that raw milk was not for them – can’t say that I blame them, I loathe milk – which had the effect somewhere along the way of turning off the gene that contains the instructions for digesting lactose.
People that live in Northern Europe, a society that still maintains a rich Milk culture (pardon the pun, I am not referring to yogurt), have switched-on genes for digesting lactose. They do not suffer the same gassy, cramping, and bloating that other Europeans and people of European ancestry tend to suffer from, like myself.
People in Africa, especially south of the Sahel, also tend to be lactose-friendly. The Maasai in Kenya are an example of a culture where lactose tolerance lasts throughout life.
Genetics difference between people and cultures is not limited only to whether or not they can digest milk, though. East Asians and Native Americans have variant genes that provide them with hair that is thicker than European or African hair.
Scientists hypothesize that variation among humans derive from a variety of responses, from climatic stimulus, dietary changes, and changes in geography.
Geneticist and Evolutionary Biologists are faced with many research problems. Of the 20,000 or so genes in the human genome, most are not understood. The genes can be broadly classed but specific functions and interrelationships with other genes is still a mystery.
Culture makes us who we are today. According to some scientists though, cultures 20,000 years ago or more, also had a hand in making us who we are today, too.