Lactose tolerance evolved three times, according to articles in ScienceNOW 11 December 2006 and Science, vol. 314, p1672, 15 December 2006.
Lactose tolerance is the ability to digest milk in adult life, and depends on the activity of an enzyme named lactase that breaks down lactose, the sugar in milk. In most of the world’s population the enzyme is turned off in adult life, and drinking fresh milk causes digestive upsets. However, some people groups in Europe, the Middle East and Africa can digest milk throughout adult life.
In 2002 scientists found a variation in a gene that regulates production of lactase in Northern Europeans that enables them to tolerate lactose as adults. Researchers then looked for the same variation in other populations that drink milk but could not find it in Africans and found only low levels of it in southern Europeans and Middle Eastern people. They then identified the gene in Europeans and then looked for the same stretch of DNA in a number of African groups. They found three other variations which had the same effect as the European variation.
The researchers claim this is an “elegant example of how evolution can find different solutions to the same problem, especially in the face of strong selection.” Anthropologist Ken Weiss of Pennsylvania State University commented: “There is not just one way to tolerate milk, but several ways. It (the DNA study) is very nice work because it shows that evolution isn’t just about picking one gene and driving it.”
Editorial Comment: The gene discovered in 2002 is a control gene that turns off the production of lactase after childhood. The “variations” found in the people who can digest lactose as adults are mutations that stop the gene from functioning, so that the lactase producing gene never gets the signal to close down.
This new study is not evidence for evolution. Just as there are various ways you could accidentally stop an electronic control device from working, e.g. stamping on it, or pouring a cup of coffee into it, there is more than one way to make a control gene cease functioning. This is not evolution, it is genetic breakdown, and is good evidence that human beings are degenerating, i.e. losing functions, not evolving new ones.
One editor of this newsletter wrote a very unpopular article (particularly with theologians) in the early 80’s entitled “Did Adam Drink Milk?” (Ex Nihilio Vol 4, June 1982, pp9-13) which concluded that the ability to drink milk in adulthood is a degenerate loss. This is another example of the predictive value of creation based research. Of course, it means the study described above should be labelled Lactose tolerance devolved three times. We also predict this loss could occur yet again in any human group as the world and the human genome continues to go downhill.
Evidence News 13 February 2008
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