Paleoanthropology: an exact science?
In his book In the Footsteps of Eve Dr Lee Berger considers "a line of couples representing the 200,000 generations of hominids that have lived on the Earth since bipedalism began." He points out the difficulties of identifying morphological changes across the 400,000 individuals from the "existing fossil record" which represents "fewer that 5,000 individuals" many of whom are not actually part of that direct heritage. In addition, the fossil record occurs in clusters, both geographically and chronologically -- paleoanthropologists are essentially joining dots to make a recognisable picture. That they are prepared to make claims about the evolution of modern humans based on such sparse evidence must require a degree of arrogance that would be frowned upon by other sciences.
The story of hominid evolution is also a fickle one. When Raymond Dart discovered the first example of Australopithecus africanus (the now famous Taung child) in 1924 (additional examples, such as Robert Bloom's discovery of Mrs Ples, were found in the Sterkfontein Caves) the field of paleoanthropology blossomed and a pattern of human evolution was proposed. This was, unfortunately for Dart, abandoned when Australopithecus afarensis (Lucy) was discovered in the Hadar region of Ethiopia in 1974. Africanus was no longer in the running as our ancestor but was relegated instead to the sidelines, whilst afarensis was promoted to the premier spot. Every discovery since has been fitted to this pattern -- with almost 20 recognised genus of hominids now included in the Homo sapien sapien "family tree".
The pattern is, of course, in dispute: the role of Homo neanderthalensis is considered a dead-end by most paleoanthropologists, but is still held to be significant by a few renegades, and Australopithecus africanus is considered to be the direct ancestor of choice by those who consider South Africa to be the "Cradle of Humankind". Paleoanthropology often seems to be based more on personality and loudness of voice than hard science.
Two major discoveries in Kenya added to the debate about the human family tree. In October 2000 the Kenyan Palaeontology Expedition, composed of Kenyan and French scientists, discovered 13 fossil fragments in the rocks of the Tugen hills. These rocks are known to be six million years old, and if the Orrorin tugenensis is recognised by the scientific community, it will become the earliest example of bipedalism yet discovered. At the moment Ardipithicus ramidus, dated to around 4.5 m.y.a. (million years ago), holds this title.
The second discovery, more rapidly accepted by the scientific community, was announced by Meave Leakey of the National Museums of Kenya and her colleagues. Kenyanthropus platyops (the flat faced man of Kenya) was discovered on the western shore of Lake Turkana in northern Kenya. The strata from which the fossil skull has been removed are dated to between 3.5 and 3.2 m.y.a. It is claimed that Kenyanthropus platyops represents a completely new branch of the family tree.
In February 2001 paleoanthropologists in Ethiopia unearthed a well-preserved partial skeleton (including the all-important skull) of a young hominid from strata dated to 3.4 million years ago. The dig was in the Afar region, south of the famous Hadar site where Lucy was discovered. The age of the hominid puts it roughly half way between Lucy (3.2 m.y.a.) and similar fossils found in Laetoli, Tanzania (3.7 m.y.a).
'New hominin genus from eastern Africa shows diverse middle Pliocene lineages' -- a technical article in Nature by Meave Leakey et al. which reports on the discovery and classification of Kenyanthropus platyops.
Daniel E. Lieberman's Nature article 'Another face in our family tree' gives a more accessible view of the implications of these recent discoveries.
In the Footsteps of Eve by Lee R. Berger Ph.D. and Brett Hilton-Barber, Adventure Press, National Geographic, Washington, D.C., ISBN 0 7922 7682 5, 325 pages.
This article was originally published on the web on 11 May 2001.