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Interpretation of fossil finds and what they imply about human evolution often means different things to different scientists. To many, evidence shows that the sequence of species in the Homo genus followed a linear route, fromHomo habilis to Homo erectus and eventually to Homo sapiens. To other scientists, the fossil record points to a bushy, branching tree rather than a single stem. Two new fossil finds from the rich deposits around the Koobi Fora ridge in Kenya’s Lake Turkana basin add more conclusive evidence that our ancestral tree branches and that species often occupied the same time periods and the same regions. Some species evolved on their own paths and died out, leaving no ancestors, while others eventually developed into new species.

The discovery team, which was led by University College London anthropologist Fred Spoor and Meave Leakey of the National Museums of Kenya, has identified the fossils as belonging to Homo habilis and Homo erectus. The fossils dated to similar time periods, supporting the notion that multiple species coexisted in this lake basin, and that they did so for almost half a million years. This Human Bulletin places these fossils in context with other Homo species and ancestral path to humans.

Class Discussion

Display the hominid “family tree” diagram from the Hall of Human Origins web site:

Point out to students that in some cases the branches of the family tree do not connect. Explain that science is a dynamic process and as scientists find more evidence those links may change or be connected. Draw students’ attention to Homo ergaster, Homo erectus, and Homo habilis on the diagram. Explain that the Snapshot will provide new evidence regarding these species.

Have students view the snapshot and read the synopsis. You can use the following to guide a class discussion.

  • Many scientists theorize that the sequence of species in the Homo genus follows a linear route. Describe this sequence.
  • Other scientists theorize that the fossil record shows the sequence of species in the Homo genus as a branching tree. Describe this sequence.
  • What does this new evidence indicate?
  • Which of these theories does the new evidence from Lake Turkana support?

Students who wish to learn more about this subject can visit the Anne and Bernard Spitzer Hall of Human Origins web site at: