The digestion of milk in human beings is facilitated by the enzyme lactase, which breaks the indigestible lactose found in milk into digestible components; glucose and galactose. Lactase is secreted in large amounts in infants because they survive solely on breastfeeding. They need an overdose of lactase to aid in digesting the mother’s milk. After infancy, however, grown up children, like adults, start eating a variety of foods whose digestion does not depend on lactase. Consequently, the secretion of lactase slows down because it is no longer needed by the body for metabolic processes. However, due to social-economic and cultural diversity, different groups of people adopt different dietary lifestyles, which influence the kinds of food they eat (Kittler, Sucher, and Nelms 12). In this case, nomads and pastoralists who depend on animal rearing tend to drink more milk and on a more frequent trend than those who lead settled lifestyles, such as urban dwellers. The human body is apparently a very adaptive machine; while lactase is no longer available in sufficient amounts in adults, the body must find a way to digest the milk its system receives. Accordingly, the body’s adaptive mechanisms converge with evolutionary processes to trigger gene mutation in the DNA strand associated with the production of lactase (Check 995). Consequently, people who consume consistently develop a condition known as “lactase persistence,” the ability to continue producing lactase throughout their adult lives. In this regard, people who tolerate milk (such as pastoralists) do so because their dietary lifestyle- frequent intake of milk, triggers gene mutation in the DNA strand associated with lactase. This condition induces the body to continue producing lactase, a process that normally ceases after infancy. In contrast, this kind of mutation does not take place in adults who do not take milk frequently, hence their inability to tolerate milk; their lactase levels are insufficient to aid milk digestion.
This genetic changes show that the evolutionary history of milk tolerance in human populations follows migration and settlement patterns of the early man as well as prevalent economic activities. It also shows that milk tolerance is associated with cultural practices. Consequently, milk tolerance is high among pastoralist groups because their diet consists mostly of milk products. This discovery provides an alternative explanation to natural selection, besides the environmental approach adopted by Darwinism. While Darwinism emphasizes on environmental factors to explain how human beings survived over time, the discovery of gene mutation to explain milk tolerance shows that biological adaptations and cultural practices also play a role in evolution.
Given this understanding of milk tolerance, it is clear that the extinct Homo neanderthalensis who survived on hunting and gathering could have developed mechanisms to tolerate milk if they consumed it frequently. Although at first they could not produce lactase, consistent milk intake could have triggered gene mutation to induce lactase secretion. Future generations would have been endowed with the lactase gene from infancy through hereditary inheritance. On the reverse side, milk tolerance will disappear if a generation stopped taking milk due to the availability of other foods. This is because the body will have little use of lactase, and the gene associated with its secretion will become obsolete. As a result, it will be absent in future generations because the human DNA could have evolved to produce only genes that are necessary for survival.