1 million to 500,000 years ago: A fossil in the African gap
In June 2003, our Smithsonian research team uncovered an early human skull from the site of Olorgesailie, Kenya, dated to about 900,000 years old. The find is the first fossil clearly dated to a 400,000-year gap in the human fossil record of Africa. The gap, between 1 million and 600,000 years ago, is a critical time of human evolution in Africa prior to the origin of our species, Homo sapiens.
The
Olorgesailie cranium (A: two views of the frontal bone; B: two views of
the temporal bone) is similar to the best known fossil human of this era,
known in Asia - Homo erectus. Some researchers think that multiple
species occupied the human family tree between 1 million and 500,000 years
ago. Yet our fossil also shows unique traits, without precedence in any
other finds. This makes it hard to assign the fossil to any one species.
In fact, it suggests that during the process of evolution, new traits
developed as groups became isolated, but then these traits mixed and blended
with others as groups spread and came into contact again - repeatedly
for thousands of generations.
The fossil was unearthed in a layer in which stone handaxes typical of Acheulean technology occur. In fact, Acheulean stone tools are present in many layers at Olorgesailie between 1.2 million and 490,000 years ago. Even though we have only the one fossil, the toolmakers at Olorgesailie were apparently able to survive large and repeated changes in the climate and landscapes of southern Kenya. For more information about this, please see our Dispatches from the Field 2004.
Small Mid-Pleistocene Hominin Associated with East African Acheulean Technology. Published in Science (2004), vol. 305: 75-78. By Rick Potts, Kay Behrensmeyer, Alan Deino, Peter Ditchfield, and Jennifer Clark.