I would direct you to the Smithsonian Institution. Although the data are confusing, it is clear that our earliest ancestors started walking on two legs — the first step (no pun intended) toward homo sapiens — about 4–5 million years ago.

Here is the link:

http://humanorigins.si.edu/education/introduction-human-evolution

Thanks for the great question!

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Mike is an Assistant Professor of Management for Legal and Ethical Studies at Oakland U. Mike combines his scholarship with practical experience in politics.

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