Disease is bad, right? But what if some diseases are a direct byproduct of human adaptation? Discover's Gene Expression blog says we should consider disease as a byproduct of adaptation to our environment. Take sickle-cell anemia, for example. There is no doubt that this is a condition that can kill the carrier. But it is also a by-product of our adaptation to endemic malaria, the blog says. "Sickle-cell disease one of the classical illustrations of heterozygote advantage, whereby those who carry one copy of the mutation on the gene have increased fitness vis-a-vis those who carry two normal copies of the gene," Gene Expression says. "The increase in frequency of the mutant gene though is balanced by the fact that mutant homozygotes have decreased fitness." And though in many cases, the side effects of genetic changes are benign, there are cases where the byproduct is a disease.
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