Lowly Origin: Where, When, and Why Our Ancestors First Stood Up. Jonathan Kingdon. Princeton University Press, Princeton, NJ, 2003. 408 pp., illus. $49.50 (ISBN 0691050864 cloth).
The first systematic review of the anatomical differences between modern humans and the African apes, the chimpanzee and gorilla, was by T. H. Huxley in 1863. In an essay entitled “On the Relations of Man to the Lower Animals,” which forms the central section of his book Evidence as to Man's Place in Nature, Huxley sets out his conclusion that the anatomical differences between modern humans and the chimpanzee and gorilla are less marked than the differences between the two African apes and the orangutan. Charles Darwin drew upon this evidence when, in 1871 in The Descent of Man, he suggested that the ancestors of modern humans were more likely to be found in Africa than elsewhere.
Developments in biochemistry and immunology during the first half of the 20th century allowed the search for evidence about the nature of the relationships between modern humans and the apes to shift from traditional gross morphology to the morphology of molecules. The earliest attempts to use proteins to determine primate relationships were made just after the turn of the century, but what Linus Pauling called “molecular anthropology” did not get into its stride until the early 1960s. Two scientists, Morris Goodman and Emil Zuckerkandl, made important contributions to this research. Goodman used techniques borrowed from immunology to show that the albumins of modern humans and chimpanzees were so alike that one could be confused with the other. Zuckerkandl employed enzymes to break hemoglobin up into its component peptides, and then used chromatography to demonstrate that the patterns made by the peptides from a modern human, a chimpanzee, and a gorilla were indistinguishable. A little later, Vince Sarich and Alan Wilson suggested that the modest differences in the serum protein albumin that separate modern humans from the living African apes may well have taken little more than 5 million years to accumulate.
By the late 1980s, advances in molecular biology meant that the differences between ape and human could be explored at the level of the genome. Studies of DNA hybridization confirmed that modern humans, chimpanzees, and gorillas were closely related, and subsequent DNA sequence analyses have confirmed Goodman's hunch that chimpanzees are more closely related to modern humans than to gorillas. Researchers cannot agree about the best way to calibrate the divergence of the chimp and human lineages. Estimates range from 5 million to 12 million years, with the early date having more adherents than the later one.
The impressive predictive power of biochemical methods contrasts with the dearth of fossil evidence about the history of the Pan–Homo clade. You will search the paleontological literature in vain for any fossils that are claimed to represent either the common ancestor of the Pan–Homo clade, or of any creatures belonging to closely related clades. Nor will you find any fossil evidence that has been assigned to the chimpanzee part of the Pan–Homo clade. Most scenarios that purport to “explain” the origin of the human clade have either been refuted by paleoenvironmental evidence (e.g., taxa that almost certainly belong to our own, hominin, clade are not confined to savannah environments), or they are so far-fetched that researchers are loath to devote time to refuting them.
Jonathan Kingdon is not a member of the early hominin Mafia, and that alone makes him singularly well equipped to cast an eye over the thorny problem of human origins. He was talent-spotted by Julian Huxley, who, impressed by Kingdon's knowledge of the wildlife in Uganda's National Parks, suggested that he should abandon teaching fine arts at Makerere University and switch to zoology. Thankfully, Jonathan Kingdon did not altogether abandon fine arts, and he is well known for combining his zoological and artistic talents in books that capture the essence and evolutionary context of African wildlife in a unique way.
The short title of Kingdon's latest book uses the last two words of Darwin's Descent of Man. Darwin ends the book by giving his readers a lesson in evolution and reminding them that “man still bears in his bodily frame the indelible stamp of his lowly origin.” In case you miss the literary reference, the author helpfully subtitles the book “Where, When, and Why Our Ancestors First Stood Up.” Scientists are supposed to eschew the “why” questions, but Kingdon sensibly casts these fetters aside and tackles the “why” question with gusto. Nor does he shy away from controversy.
There is presently a substantial schism in the early hominin Mafia family. The West Coast side of the divided family takes anagenesis (the process by which one species evolves into a new species) as its null hypothesis. According to this view, all fossil hominins belong to a single lineage of time-successive taxa unless proved otherwise. The null hypothesis of the East Coast faction is quite different. Recognizing that the evolutionary history of most other mammals is complex and “bushy,” this faction holds that even if we were sure that the existing hominin fossil evidence faithfully represented all the diversity that has ever existed, we could not reconstruct the branching pattern with any confidence because it, like that of most mammalian taxa, is too bushy. Thus the prejudice of the East Coasters is a form of uniformitarianism: It rests on the essential similarity of evolutionary branching patterns in different taxa. In this view, a simple linear explanation of human evolution flies in the face of a more complex comparative reality.
The West Coast branch of the family accuses their East Coast relatives of being unscientific, and of doing “X files” paleontology. The East Coast family are generally more tolerant of their West Coast colleagues and, even when provoked, their harshest criticism is that the West Coasters tend to interpret the world in too simplistic a fashion. Jonathan Kingdon has never been a fence sitter, and in this instance he comes down unequivocally on the side of the East Coasters. He cites evidence of many living animals that show at least as much, and probably more, taxonomic diversity than that envisaged by the East Coasters. His scenario is as follows. The ancestor of the Pan–Homo clade returned to Africa from Asia about 10 million years ago. By this time it was much less dependent on trees for its habitat, and Kingdon thinks that its niche was, or became, that of a ground-dwelling ape, trunk erect and carefully sifting through the forest floor for foodstuffs. The taxonomic diversity some see in the hominin fossil record would have come from the effective isolation provided by the patchwork quilt of eight or so major lake basins scattered across Africa.
Kingdon has read widely and wisely. There are a few glitches in his book: Most of the sensation in the face travels with the three divisions of the trigeminal nerve, and it is the mammalian middle ear, not the inner ear, that has complex homologies with the jaws of earlier vertebrates. But these are trivial concerns and the confusions are uncharacteristic. The text is riddled with evidence that Kingdon is one of the few people who have the breadth of interests and the practical knowledge of contemporary African wildlife to comment authoritatively about the ecology and diversity of its flora and fauna.
In Chicago's excellent Field Museum, there was (and maybe still is) an exhibit about Africa. To try and convey the sheer size of that continent, an outline of Africa has been traced on the floor. Within it, to scale, are the outlines of many other parts of the world that we routinely think of as big (e.g., North America, India, Australia). Jonathan Kingdon's Lowly Origin does justice to the immense task of trying to convey the actual and potential complexity of the evolutionary history of Africa's fauna. The West Coasters think we are close to knowing all there is to know (at least in terms of taxonomic diversity) about the early stages of human evolution, whereas the East Coasters think, at least in relation to the early stages, that we are just beginning to scratch the surface of the fossil evidence. Kingdon's book shows the value of the perspective of a careful student of “old-fashioned” natural history. The author does not claim to have found the answer to human origins. The real message of the book is the rich contextual evidence it provides. Wise students of human evolutionary history would be well advised to think carefully about that message.
