Charles Darwin claimed that all terrestrial life shares a common ancestry and that the wide array of living species can be accounted for by a process he called "natural selection." By sheer accident, the members of any generation of a given species will differ from one another, and nature will "select" only those able to survive and bear offspring themselves. Over immense periods of time, the selection and inheritance of minute advantageous variations in adaptability will bring about countless new and distinct forms of life, including eventually humans.
Darwin published On the Origin of Species almost a century-and-a-half ago, but today the majority of biologists still commend it for its general accuracy. In a synthesis known as "neo-Darwinism" they have simply added to Darwin’s original ideas our more recent knowledge of genetics. Important internal disputes still divide evolutionary biologists, but in the scientific community today there is an abiding appreciation of Darwin’s genius and the fundamental correctness of his ideas about life’s shared ancestry and the mechanism of natural selection. Opinions differ about the roles in evolution played by chance, adaptation, selection, genes, individual organisms, populations, struggle, cooperation, competition, etc. But most scientists today do not doubt that life has evolved-at least roughly-along the lines that Darwin brilliantly laid out.