Recent Human Evolution - Lactose Tolerance

Humans, like other mammals, feed their young with milk from excretion glands (breasts). The predominant sugar in milk is lactose, and like any other complex sugar, it requires the production of an enzyme, which in this case is lactase. Lactase breaks lactose into simple sugars; glucose and galactose. Obviously the genome contains a section of coding which creates the lactase enzyme. Since most mammals stop consuming milk excretions once they get to a certain age, and their is no other source of lactose other than milk, the costly production of lactase is of no use. Therefore, in most mammals, including most humans, the genes that produce lactase are switched off. This is the cause of lactose intolerance, whereby adult humans are unable to digest the main ingredient of milk, lactose.

Humans are unusual compared to other mammals in that, among the human tribes that have domesticated milk producing cattle, they continue to consume milk as a nutritional source (sometimes the MAIN source) as adults. Based on evolution we would then be able to make a prediction; any human tribe that has domesticated cattle will have a greater ability to digest lactose. Further that they will do this by continuing to produce lactase as adults.

This prediction is indeed confirmed, in humans from populations with a long herding history, mutant forms of the lactase gene continue to operate into adulthood. Also this mutant ability is never present in any of the human tribes which did not develop herding, such as Australian Aborigines, who are all lactose intolerant. Evolutionary theory says that this is an example of how mutations can be beneficial and add information to the genome. A creationist however would say that god created all humans with the ability to produce lactase but "after the fall" humans devolved, and so some populations lost this ability. In other words, Aborigines are devolved Europeans. How can we disprove the creationist on this point?

Simple, because evolution makes another prediction in this matter. Since history says that herding, as a cultural innovation, arose independently among different human tribes, evolution predicts that the mutation that allows continuing production of lactase will be a different mutation in each case. Once again this is confirmed. Herding was invented independently by groups in Europe, Africa and the Middle East, using milk derived from cattle, camels, and goats.  These populations all have evolved lactose tolerance, but with strikingly different mutations to their lactase genes. So we can then ask the creationist which version of lactose tolerance Adam was created with, then we have proved that all the others MUST have evolved.

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