Debunking the Thrifty Genes Hypothesis

We now need to address the issue of why risk alleles are found at a common frequency in the human genome. There are logically three possibilities. First, they are just drifting around, too inconsequential for natural selection to pay much attention to. Second, a balance between the advantages and the disadvantages they confer may actively keep them around. Third, some of the alleles may be truly beneficial, but they are too young and there has not yet been enough time for them to displace the old ones. Evidence is accumulating that all these mechanisms are involved.

Let’s start our discussion, though, with an explanation that you might have read about in the Sunday papers, the so-called “thrifty genes hypothesis.” ...

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