For several million years our ancestors were hunter gatherers, living on game, wild plants and honey. Then, around 10 to 11 thousand years ago, the first agricultural communities developed in Anatolia (present day Turkey) and around the Black Sea. The earliest crops likely included early types of wheat and barley. In essence, these cereals are carbohydrates that contain starch. However, early humans could not break down starch that easily. It is thought that around that time a mutation occurred that provided some advantages to the early agricultural workers by allowing them to digest the wheat and barley more easily. Specifically, the salivary glands produce an enzyme that breaks down starch and there is evidence that there were mutations that occurred that resulted in the gene getting multiplied to several-fold more, resulting in the better ability to break down starch. One advantage is that by breaking down the starch in the mouth, it would generate glucose, which provides a sweet taste that would make the food more attractive. It also would tend to increase the blood glucose levels faster, that we know could improve the ability to gain weight. Today some studies show that the mutations that allow us to eat starchy foods are higher in agricultural communities as opposed to hunter-gatherer groups.
Similarly, the introduction of domesticated goats, sheep and cattle resulted in pastoral living in which it was necessary to be able to digest milk and cheese. However, while babies drink breast milk, the ability to ingest milk goes away as we get older. This is because there is an enzyme that helps us break down milk (lactase), and as we get older we lose the ability to make it. However, there were mutations in lactase that resulted in the continued production of lactase into adulthood, and this allowed individuals to continue to eat milk and cheese as adults. Today the majority of individuals carry some lactase and are able to digest milk and cheese. However, some individuals do not produce enough lactase and are “lactose intolerant”. These individuals can still drink milk if it is supplemented with lactase.
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- Ranciaro, A., Campbell, M.C., Hirbo, J.B., Ko, W.Y., Froment, A., Anagnostou, P., Kotze, M.J., Ibrahim, M., Nyambo, T., Omar, S.A. and Tishkoff, S.A. (2014) Genetic origins of lactase persistence and the spread of pastoralism in Africa. Am J Hum Genet 94: 496-510.