Louis Leakey and human evolution

The following drawing comes from Louis Leakey's 1934 book Adam's Ancestors, and shows how he believed human evolution had occurred.

Evolutionary tree from Adam's Ancestors

What is striking about this drawing is just how wrong it is, on so many counts. In this diagram, all of the living apes branch off from humans at the same time, and very long ago -- in the mid-Oligocene, or about 30 million years ago. Nowadays, it is believed that humans diverged from gibbons first, maybe about 20 million years ago, then from orang-utangs, then from gorillas, then from chimpanzees between 5 and 8 million years ago.

Also striking is how almost all of the hominid fossils known at that time (Java Man, Peking Man, the Heidelberg Jaw, Rhodesian Man, Neandertals) are far, far away from the line of human ancestry. All of these, according to Louis, belonged to a branch of 'Paleoanthropidae' (ancient men) that had diverged from the 'Neoanthropidae' (new men) long ago in the Miocene (at least 15 million years ago, in modern terms). Nowadays all of these are considered either ancestral at least quite close to it, and would have diverged from modern humans maybe 2 million years ago for the Homo erectus specimens, and much more recently for the other specimens.

There are only a couple of fossils that Leakey accepted as being on or near the lineage of "true man". One was Louis' own "Homo kanamensis", named from a few fossils found by Leakey's team in 1932 at Kanam and Kanjera. The other, just off the main line of human ancestry, was the fraudulent Piltdown Man, with its apelike jaw and human skull. At the time, Piltdown was still accepted as a valid fossil. The Kanam and Kanjera fossils would be discredited within a few months of the release of Adam's Ancestors, when Leakey was unable to document where they had been found to a visiting British scientist (an incident which did massive damage to his credibility and reputation as a scientist). The Kanjera fossils are now thought to be modern human bones buried in older sediments, while the Kanam jaw is old but not as modern as Louis thought.

Piltdown may have played a role in this, but one can't attribute Leakey's ideas entirely to his acceptance of Piltdown. Throughout his life, Louis Leakey always had a deep conviction that humanity had an ancient lineage. (Leakey was by no means alone in this; his mentor at Cambridge, Sir Arthur Keith, and Solly Zuckerman had similar views.) Even after Piltdown was recognized as a fraud in 1953, Leakey still continued to put most hominid fossils well off the line of "true man". For him, australopithecines and Homo erectus were extinct offshoots, too overspecialized to be human ancestors. The line of true humanity went through Homo habilis, which had been discovered by the Leakeys in the early 1960's at Olduvai Gorge. (Leakey 1966)

Another final interesting point about Leakey's diagram is the ordering of the human races: Australoid, Negroid, Mongoloid, and European. Looking closely at the drawing, one can even see that these races seem to have differentiated from the Neoanthropidae stem at different times, with the 'advanced' races doing so slightly before the 'primitive' races. Leakey was hardly a bigoted racist; he had been raised and initiated as a member of the Kikuyu tribe and spoke Kikuyu as a native. But he could not, apparently, break free of the prevailing wisdom that races could be ordered, and Europeans were the most advanced race. The theory of evolution was not, of course, the cause of this belief. It had always been considered (by Europeans) to be self-evidently true, and the theory of evolution seemed to provide a ready explanation for what was already 'common knowledge'. (see Gould 1983)

References

Gould S.J. (1981): The Mismeasure of Man. New York: W. W. Norton.

Leakey L.S.B. (1934): Adam's ancestors. London: Methuen & Co.

Leakey L.S.B. (1966): Homo habilis, Homo erectus and the australopithecines. Nature, 209:1279-81.

Lewin R. (1987): Bones of contention: controversies in the search for human origins. New York: Simon and Schuster. (discusses in detail some of the major controversies that have occurred in paleoanthropology)

Biography of Louis Leakey

This page is part of the Fossil Hominids FAQ at the talk.origins Archive.