Fossil & Geologic Evidence: Bipedalism vs. Brain Size

For years anthropologists struggled with the question as to what role larger brains played in the evolution of bipedalism. Beginning in the late 1800's until the early 1900's, almost all known fossil bipedal hominins had relatively larger brains. Then, in 1924, Raymond Dart found the first australopithecine, known as the Taung Child in South Africa. This specimen belonged to the species A. africanus and had relatively a small brain similar to that seen in modern chimpanzees. However, only a partial cranium of the Taung Child was recovered and bipedalism was determined based on the inferior position of the foramen magnum. Since evidence remained scant, debate about the timing of bipedalism and brain size continued.

However, in 1974, Donald Johanson found the nearly complete fossilized skeleton of Lucy, a member of the species A. afarensis dating to 3.2 Ma. Lucy was unique at that time, b because she exhibited both a small brain, similar to that of modern chimpanzees, and the highly derived features characteristic of bipedalism, similar to humans. As other contemporaneous and older fossils (perhaps as old at 7 million years) are found, scientists have revised the bipedalism timeline. Today, the evidence undoubtedly demonstrates that bipedalism was the first hallmark of the hominin lineage. One of the advantages of bipedalism is the freeing up of the hands to produce more technologically advanced stone tools which may have lead to a better diet that affected brain size.^8-10,27-29