In my September 2011 ABT Editorial that argued that humans are all one race, there was a reference to human evolution beginning some 100 million years ago. The date is obviously incorrect, and a colleague at St. Clair County Community College in Port Huron, Michigan, David Sheldon, astutely called this to my attention. I therefore offer the following synopsis of the chronology of human evolution. This represents the apparent scientific consensus and may be helpful as a teaching tool when addressing human evolution with students.
Early hominids (great apes) probably came from apes similar to the chimpanzee ca. 5–10 million years ago. Remains of familiar hominids such as Australopithecusafarensis and A.africanus have been dated from 3–4 and 2.5–3 million years ago, respectively. The first humans (genus Homo), including Homo habilis (handy man), evolved in Africa ca. 2 million years ago. The earliest fossils of H. erectus were found in Indonesia and dated to ca. 1.8 mya. Homo erectus and all previous members of genus Homo were extinct by 70,000 years ago. Homo neanderthalensis (Neanderthal man) lived from ca. 250 to as recently as 30,000 years ago, at which time they were displaced by Cro Magnon man in Europe. They walked entirely upright but were shorter, stouter, and probably stronger than today’s humans. Neanderthal man is probably the source of the mythic “caveman,” but Neanderthal man neither lived in caves nor coexisted with dinosaurs as suggested in fictional media. And there is no evidence that Neanderthal man was hairy like a gorilla.
Cro Magnon man (Homo sapiens, or wise man) evolved some 40,000 years ago, so it is possible that Neanderthal man and early H. sapiens actually coexisted for a while. They may even have encountered each other. The H. sapiens sapiens (civilized man) that exists today is genetically similar to H. sapiens, the added “sapiens” simply denoting the human at the beginning of civilization as we know it. But the two are the same species and would have been able to successfully interbreed.
Curiously, another species of human, H. floresiensis, was very recently discovered in Indonesia. This human, nicknamed “hobbit” because of its small size (~1 m tall), appears to have lived from 100,000 to 12,000 years ago. It appears not to be closely related to modern humans, but they do share a common ancestor. All hominoids except H. sapiens have been extinct for at least 12,000 years. It is not clear why H. floresiensis became extinct.
Human, chimp, and gorilla are in the family of great apes, suggesting a relatedness among them. Humans did not come from monkeys, but both human and monkey evolved separately from a common pre-ape ancestor. The closest living relative of the human is the chimpanzee, and we likely evolved from a close relative of the chimp. This conclusion is based on modern DNA analysis and the human lineage derived from the fossil record. I will leave you with another interesting fact: The organism that has the closest DNA match to the modern gorilla is in fact the human, but the closest DNA match to the human is the chimp! Although the reason for this is not known, it suggests that the gorilla may have evolved from an ancestor of the chimp but prior to the development of the human. The human, chimp, and gorilla are all apes, not monkeys.
Thanks to Dave Sheldon for reviewing the above for me.