Early scientists theorized that brain development was the main mark of the hominin lineage. The theory on brain enlargement was refuted after the unearthing of first hominin fossils which depicted chimpanzee-sized brains and bipedally-modified morphology. Raymond Dart discovered the first australopith fossil, Taung Child, in South Africa in 1924. The Taung Child was from the species Au. Africanus and had a brain that is comparable to that of a modern-day chimpanzee. Based on the inferior placement of the foramen magnum, Raymond Dart hypothesized that the specimen was bipedal. From this, Raymond Dart hypothesized that bipedalism in early humans evolved before the development of larger brains (“Bipedalism vs. Brain Size,” 2018). Owing to the fragmented remains and small sample size, the dispute surrounding the timing of brain size and bipedalism endured for the next five decades.
However, everything changed when Donald Johanson discovered an almost complete fossilized skeleton of Lucy, in 1974. Lucy was from the species, Au. Afarensis, the species dated to approximately 3.2 Ma. From “Becoming Human - Episode 1 - First Steps” (2018), Lucy was particularly unique during this time since she was one of the first fossils which had a highly derived feature typical of bipedalism and also had a small relative brain size. As other contemporary and older fossils (possibly as old as 7 Ma) were discovered, researchers are still working to revise the bipedalism timeline. Currently, the evidence unquestionably depicted that bipedalism was one of the initial marks of the hominin ancestry, and may have led to numerous more developments. For instance, one benefit of bipedalism is that the hands are freed, that permitted for the making of more technically progressive hand tools. By developing advanced tools, led to more protein diet which may have helped boost brain development.
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References
Becoming Human - Episode 1 - First Steps (Homo Sapiens). (2018). Retrieved from https://www.youtube.com/watch?v=f00USo9sgdY
The University of Texas at Austin, D. (2018). Bipedalism vs. Brain Size | eFossils Resources. Retrieved from http://efossils.org/book/bipedalism-vs-brain-size
