Young children in rural Gambia face constant exposure to gastrointestinal and respiratory infections and, during the rainy season (July–November), suffer recurrent bouts of Plasmodium falciparum malaria. Within living memory, these conditions led to more than half of the children dying before their fifth birthday, providing a graphic demonstration of the impact that infectious diseases have had on our natural selection. Fortunately, these horrific statistics have been decreased greatly by improved medical care, especially through vaccination and anti-malarial therapies, but conditions such as these have inevitably left a powerful imprint on man's genetic make-up.

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