nonexistent in non-European populations. It presumably achieved its sudden prominence through the natural selection caused by some serious epidemic that raged through Europe at that time.
The variant gene was discovered because it is also protective against AIDS. But AIDS is far too recent a disease to have driven the frequency of the CCR5-delta-32 variant to such a high level in the European population. That driving force was at first thought to have been the Black Death, which killed some 25 to 40% of Europeans in the years 1346-1352, and a further 15 to 20% in 1665-1666. But it now seems that smallpox, which in the long term killed a larger number of people though in less
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