Archaeologists working in Kenya's remote Turkana basin are using the latest analytical techniques and theories on human behaviour to fill in many of the gaps in the evolutionary record. And as Terry Hardaker explains, there's more than a missing link in the transition from apes to humans
Since the time of Charles Darwin, the quest to discover our human origins has exerted a strong pull over archaeologists and anthropologists. Until relatively recently, however, progress in this field had been agonisingly slow. It is only in the last 40 years that East Africa has been pinpointed as the most likely location for the transition from apes to hominids.
Though we continue to use the term "missing link", it looks increasingly as though "missing links" would be more accurate. And the search for these is hindered by the fragility of human bones and the fact that they are seldom preserved for long.
Many of the richest sites of human remains are difficult to reach, even today. And when finds are made, they have to be fitted into a vast time scale; depending on how we define the term "human", we are looking at a period of initial hominid development of between six and three million years ago. It is for all these reasons that the story of human evolution is still like an enormous jigsaw with most of the pieces missing -- and no picture on the box.
A team of researchers from France and Kenya, headed by Dr Helene Roche of the Centre National de la Recherche Scientifique in Paris, and Dr Mzalendo Kibunjia from the archaeology division of Nairobi Museum, has mounted a series of expeditions to the western shores of Kenya's Lake Turkana since the late 1980s. The aim of the West Turkana Archaeological Project is to discover traces of early hominids, particularly stone tools, preserved in fossil sediments of earlier lake shores in the same area.
It is an arid, remote region occupied by the seminomadic Turkana tribes whose contact with the outside world remains limited. Until the 1960s, the "jade sea" of Lake Turkana (formerly Lake Rudolf) was seldom viewed by Europeans. Even now, with a road running to the lake, it remains out of the reach of most travellers.
It takes two days to reach the lake from Nairobi by 4WD vehicle. As a consequence, the eight week-long expeditions have to be virtually self-sufficient. The local Turkana provide labour for kitchen and camp jobs, and sometimes assist with fieldwork.
Despite being well equipped -- the expedition carries the world's most sophisticated GPS survey equipment (see box) -- the European soon finds himself incapable of performing what for the Turkana are simple tasks. These include finding the right spot to dig for drinking water, walking across a few miles of wilderness without getting lost, and keeping clean without the use of a bath.
To explain why we travel to this region to look for prehistoric sites, we must go back 20 million years. At that time, sub-Saharan Africa was covered with dense tropical forest from coast to coast. This was occupied by a rich variety of game including primitive apes. Geological forces were starting to tear the continent apart, opening up a gigantic fissure that would eventually run from the Jordan Valley in the north, to Lake Nyasa (now Lake Malawi) in the south. The creation of this -- the Great African Riff Valley -- provoked two major events, both of which are thought to have played a key role in the transition of apes to early hominids.
Firstly, it threw up mountain chains which broke the forest canopy and produced a more open environment. Secondly, it created a "rain-shadow" area in the east, preventing moist, tropical, westerly winds from penetrating beyond the mountains. This further contributed to breaks in the forest cover. Tree-dwelling apes were, for the first time, faced with a landscape where trees were not continuous. Their eventual response was to stand up and walk on two limbs. …