“The prevalence of primary lactose intolerance is estimated to be 7 to 20% for people of Caucasian descent, 65 to 75% for African descent, over 90% in some Asian populations and approximately 70% in Australian Aboriginal populations.” – virtualmedicalcentre.com

I’ve always found the prevalence of lactose intolerance to be really interesting. As a caucasian, I fall into the 80% that can down a gallon of milk with no side effects, whereas I can’t think of a single asian friend who isn’t lactose intolerant. One of the most interesting things about lactose intolerance is that many scientists believe lactose tolerance to be our most recent evolutionary developement. 

“The common ability of people in Europe and some other areas of the world to continue producing lactase as adults is very likely a relatively recent evolutionary development.  Prior to the domestication of cattle, sheep, goats, and horses, which occurred after about 9000 years ago, milk was most likely only consumed by babies and very young children.  That milk was human milk.  Dairy products such as cow’s milk, yoghurt, and cheese did not exist.  When nutrient rich nonhuman milk became widely available in pastoralist societies, the rare genetic variations that allowed some adults to easily digest lactose were selected for and this trait became more common.  In other words, natural selection gradually shifted to favor lactose tolerant people, resulting in the progressive evolution of the gene pools of these populations in Europe.”  – “Nutritional Adaptation” by antro.palomar.edu