Evolutionary biologist George Williams died last week, reports the New York Times. He was 83. In his 1966 book "Adaptation and Natural Selection," Williams laid out his argument that natural selection works at the level of the gene and individual, writing that "one should assume the adequacy of the simplest form of natural selection unless the evidence clearly shows that this theory does not suffice." The idea, the Times adds, was popularized in Richard Dawkins' "The Selfish Gene." Evolutionary biologist Douglas Futuyma tells the Times that Williams was "widely regarded by peers in his field as one of the most influential and incisive evolutionary theorists of the 20th century."