Photo: Human Genome Shows Proof of Recent Evolution, Survey Finds

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DNA, or deoxyribonucleic acid, is a molecule made up of chemicals called bases (A, T, G, and C) arranged along two strands of sugar-phosphates that wind together to form a double helix.

An organism's complete set of DNA is called a genome. The human genome contains some 3 billion base pairs, which code for the approximately 30,000 genes that define a person's unique traits.

New scans of the human genome have revealed widespread signs of recent evolution by natural selection affecting a broad range of characteristics from the ability to digest milk to skin color.

Illustration courtesy U.S. Department of Energy Human Genome Program

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