Humans evolving in Tibet, according to an article in news@nature and ScienceNOW, 16 Sept 2004.
Cynthia Beall of Case Western Reserve University, Ohio interviewed thousands of people living in villages in Tibet and drew up detailed family trees and medical histories. They also tested the concentration of oxygen in the villagers’ blood and found that some people were able to carry approximately 10% more oxygen in their blood. This seems to be an inherited trait that could be passed down from both parents. This means some people inherited copies of the high oxygen gene, some had two copies of the low oxygen gene and some had one of each. In high altitude Tibet the air is very thin and the ability to carry more oxygen in the blood should be a healthy advantage.
To see if there was any reproductive advantage for the extra oxygen capacity the scientists looked at the survival rates of children of mothers with high and low oxygen blood. Babies born to women with high oxygen blood had a 94% chance of surviving the first year of life, but babies whose mothers had low oxygen blood had only a 60% chance of surviving their first year. Children whose mothers had high oxygen blood were also more likely to live to the age of 15, when they were old enough to have children and pass on any inherited high oxygen genes. The scientists are not certain why the high oxygen gene confers this advantage. It may be that high oxygen in the mother’s blood enables the babies to reach a higher birth weight, or it may enable them to survive respiratory illnesses in childhood.
Emma Marris, writer for news@nature describes the findings as “a tidy example of darwinian evolution occurring as we watch”. Henry Harpending, an anthropologist at the University of Utah commented to ScienceNOW that the research revealed “a dramatic example of natural selection”. However he wondered why the low oxygen gene is still there and suggested the high oxygen gene came about recently or it has some unknown disadvantage for adults.
Editorial Comment: This is an example of natural selection, but it is not evolution. The fact that the low oxygen gene causes a disadvantage in this environment does not explain the origin of the high oxygen gene. It could be that the two types of oxygen genes only make a difference in the extreme conditions, such as in the high altitude of Tibet, and there hasn’t been enough time for the low oxygen gene to be selected out because the population of Tibet only settled there fairly recently. This would fit if all races are descendants of people scattered from the Tower of Babel.
Harpending may also be right about the gene having some disadvantage. Until scientists actually identify the gene we won’t know. Whatever the truth turns out to be the people of Tibet are not evolving. Some are simply more able to cope with living in a hard environment because of a characteristic they already had.
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