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Dr. Sarah Feakins, University of Southern California – Environment and Bipedalism

In today’s Academic Minute, Dr. Sarah Feakins of the University of Southern California explores the role environmental factors played in the origin of bipedalism. 

Dr. Feakins is an assistant professor of Earth sciences at the University of Southern California’s Dornsife College of Letters, Arts and Sciences. Her research uses biogeochemical analytical approaches to answer questions about climatic and ecological change. Her current projects include compound-specific carbon isotopic reconstruction of paleovegetation. She holds a Ph.D. from Columbia University.

About Dr. Feakins

Dr. Sarah Feakins – Environment and Bipedalism

What came first: the bipedal human ancestor or the grassland encroaching on the forest?

Human ancestors developed bipedalism—that is, the ability to walk on two legs—around six million years ago. One long-standing theory suggests that this important development was the result of grasslands replacing rain forests in Northeast Africa, where early human ancestors evolved before spreading throughout the globe. It seems makes sense: with fewer trees, being able to walk upright on the savannah would be a significant advantage. But our latest efforts to piece together what the landscape looked like casts doubts on this theory.

By studying ocean sediment cores taken in the Gulf of Aden off the coast of Somalia, we’ve been able examine about 12 million years’ worth of data about the changing plant cover of Northeast Africa. The prevailing winds blow across Northeast Africa toward the Gulf, where they deposit their load of dust. It gives us a good idea of the big picture of what was going on throughout the landscape, while the geology on land gives us a narrow snapshot of around a particular fossil when it was buried.

In the ocean sediment core, we found waxy molecules from plant leaves along with pollen. With these two pieces of evidence, we were able to determine not just what types of plants existed in the landscape throughout the past several million years, but in what proportion they existed.

What we found was that the grasslands effectively took over the landscape of Northeast Africa by around 12 million years ago. That’s six million years before hominins—early human ancestors—developed bipedalism. While it does not settle the debate over the origins of human bipedalism, it does add an illuminating new piece of evidence to consider.

Production support for the Academic Minute comes from Newman’s Own, giving all profits to charity and pursuing the common good for over 30 years, and from Mount Holyoke College.

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