Ernst Mayr, a biologist who expanded upon Darwin's theory of evolution, died on February 3 at the age of 100. While he also earned acclaim as an ornithologist, naturalist, and historian of biology during his eight-decade career, Mayr will be best remembered as a champion of evolutionary theory.

Mayr's major contribution came in 1942, when his book Systematics and the Origin of Species was published. Here, Mayr laid one of the cornerstones of the then new synthetic theory of evolution, which unified Charles Darwin's theory of evolution by natural selection with Gregor Mendel's theory of heredity. One of the shortcomings of Darwin's theory was that it didn't explain how new species appear. Geneticists who advanced Mendel's theories on heredity, meanwhile, began to look for explanations of speciation at the level of the gene.