General & History
While our ancestors certainly raided the nests of birds and reptiles for eggs from very distant pre-human times, obtaining milk from animals is a very recent development - so recent people from many regions are genetically unable to digest milk as adults (lactose intolerance (D1)).
Use of milk and milk products from animals has been a specialty of the herding peoples of Europe and Central Asia, thus few people of ancestry from this region are intolerant. On the other hand, up to 80% of American blacks, 80% to 100% of American Indians and 90% to 100% of East Asian Americans show symptoms of lactose intolerance as adults. In Southern India intolerance is nearly 70%, but in Northern India it is only about 25% due to genetic mixing with European and Central Asian peoples.Links