The missing link in human evolution?
By John Reader
A blaze of media attention recently greeted the claim that a newly discovered hominid species, Australopithecus sediba, marked the transition between an older ape-like ancestor, such as Australopithecus afarensis, and a more recent representative of the human line, Homo erectus. As well as extensive TV, radio and front-page coverage, the fossils found by Lee Berger and his team at a site near Pretoria in South Africa featured prominently in National Geographic, with an illustration of the three species striding manfully across the page. In the middle, Au. sediba was marked with twelve points of similarity: six linking it to Au. afarensis on the left and six to H. erectus on the right. Though Berger did not explicitly describe Au. sediba as a link between the two species, the inference was clear and not discouraged. The Missing Link was in the news again.
Ever since 1857, when the discovery of Neanderthal Man showed that prehistoric humans did not look like us; and 1863, when Thomas Huxley wrote that one day ‘some unborn palaeontologist [might find] the fossilised bones of an Ape more anthropoid, or a Man more pithecoid, than any yet known’ – for 150 years, the Missing Link has been a beacon of palaeoanthropological research.
For the first 100 years or so, the study of fossil humans was more of a debating society than a science, with its participants more numerous than the objects on which their interest was focused. Even in the 1950s there were fewer than a dozen fossils covering the several million years during which modern humans had evolved from an ape-like ancestor, with plenty of space (both temporal and morphological) between them for erudite speculation. Some practitioners managed to find (or even manufacture, in the case of Piltdown Man) specimens that filled the gaps with Missing Links.
Accumulating evidence (genetic as well as fossil) has shown that the ancestors who lived in Africa millions of year ago were not alone. They were one of several (perhaps many) primates whose evolutionary trajectories were similar to ours, and who lived at the same time. Untangling the fossil evidence to reveal our line of descent is a challenging task. Especially when the fossils are often so broken, distorted or incomplete that opposing interpretations of the same features can be proposed with equal validity, and the points distinguishing them may be so slight, or so ambiguous, that interpretation depends as much upon the proponent’s preconceived notions and force of argument as upon the evidence of the fossils themselves.
No surprise, then, that when a new fossil species attracts a blaze of publicity and Missing Link attribution, discerning observers are inclined take the history of the author into account as they appraise the relevance of the announcement. For instance, in the case of Australopithecus sediba, Science magazine announced the species in detail whilst also including a profile of the lead author himself, sub-headed: ‘After a career marked by controversy, Lee Berger hopes new hominin fossils will salvage his mixed scientific reputation.’
It is probably fair to say that Berger has had a chequered career, but the science on Au. sediba is sound. After all, it was good enough to convince anonymous reviewers and the editors at Science. Indeed, no one has questioned the specimen’s relevance to several important areas of palaeoanthropological research.
Interpretation is another matter, however, and here there is little expert approval of Berger’s claims, particularly in respect of the species’s transitional status. At root the issue is simple: if Au. sediba is to qualify as an ancestor of our genus, Homo, it must be older than any known Homo fossils. But, with an age of just 1.977 million years, it is appreciably younger than a 2.3 million-year-old specimen from Ethiopia which is widely accepted as the earliest known representative of our genus. Faced with that conundrum, Berger questions whether the Ethiopian specimen is, in fact, Homo. But even if it is, he says, his discovery could still represent a late surviving population of Au. sediba that led to Homo at another place and time.
This approach, seemingly offered principally to defend, not elucidate, a provocative interpretation, could be seen to diminish both its author and the science. Which is a pity, for instead of creating media hype, the discovery and study of Australopithecus sediba should focus on the study of our fossil ancestors and our greater understanding of human evolution.
John Reader is Honorary Research Fellow in the Department of Anthropology, University College London. A writer and photographer with more than fifty years of professional experience, his work has included contributions to major international publications, television documentaries and a number of books, including including The Untold History of the Potato, Africa, Pyramids of Life with Harvey Croze, and Rise of Life. His latest book, Missing Links: In Search of Human Origins, publishes this month.