The history of the evolution of life on Earth is divided into four eons: Hadean, Archean, Proterozoic, and Phanerozoic. Phanerozoic includes three eras: Paleozoic, Mesozoic, and Cenozoic. Over 4 billion years of evolution, many simple organisms, complex plants and animals have appeared. The evolution of the genus Homo lasted 2 million years. During this time many species of people appeared and disappeared. The ancestor of the first species of the human genus could be Australopithecus afarensis. The key stages of human evolution are Homo habilis, Homo ergaster, Homo erectus, Homo heidelbergensis, Neanderthal and Homo sapiens. Biological evolution is the development of wildlife. The main driving forces of evolution were discovered by Charles Darwin. He explained evolution in terms of natural selection, hereditary variation, and the struggle for existence.