Ecoscience: Primate Evolution, Humans and Gorillas

Two noted ecologists examine what's know about the history of primate evolution, in particular the relationship between humans and their nearest cousins.

| September/October 1984

primate evolution - chimp and human faces

Research into primate evolution shows humans are about equally related to chimps and gorillas.

Illustration by Fotolia/AlienCat

Although there's still considerable debate about details, the basic outlines of the past few million years of primate evolution are clear for the human line. The study of fossils has taught us a great deal about our distant relatives.

About four million years ago, our ancestors were fully upright creatures only about four feet tall, with brains of about 350 to 450 cubic centimeters (cc) in volume — roughly a third as large as those of modern people. Because the first remains of these ancestors were discovered in southern Africa and were thought to be of apes, the creatures were placed in a genus named Australopithecus — the "ape of the south."

The oldest fossil Australopithecus found so far is a creature from the Afar triangle of northern Ethiopia, who lived about three and a half million years ago, A. afarensis, discovered by paleontologist Don Johanson and his colleagues, became famous when the first fossil specimen was nicknamed Lucy, and Johanson published a fine book under that title.

Australopithecus afarensis gave rise over several million years to two subsequent australopithecine species: A. africanus and A. robustus — both of which were a little taller and had somewhat larger brains than Lucy. The last Australopithecus died out perhaps one and a quarter million years ago. But a couple of million years before that, the australopithecines had given rise to an important branch — the one leading to us.

Tracing the Human Line

The earliest known member of the Homo line was a creature called Homo habilis. It was a contemporary of the australopithecines, lived some two million years ago, stood about five feet tall, and had brain size of around 460 cc. Homo habilis was followed, about a million years ago, by Homo erectus. Members of H. erectus were quite similar to modern people; they average about five and a half feet tall and had brains overlapping size with today's Homo sapiens (700 to 1,250 cc as opposed to 1,000 to 1,800 cc)

Fossils of H. erectus are abundant and widespread, and historically have been given a variety of names including " Pithecanthropus erectus" and "Sinanthropus pekinenses." With a shave, a haircut, and modern clothing, an average male Homo erectus would probably cause little comment if seen on the street today. And there's good reason to believe that our progenitors of a million years ago also had a highly developed culture.

From H. erectus to modern H. sapiens, and its minor "neanderthal" variant, was a mere hop, skip, and jump. Indeed, the basic Australopithecus/H. erectus/H. sapiens sequence constitutes a superb fossil record, one with essentially no "missing links." It's only because of a keen interest in our own history that people even bother to search for more fossils from the past four million years of our ancestry.

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