Our dexterous thumbs have a 2 million-year-old origin

By Krista Charles

Our thumbs allow us to use a variety of tools, from hammers to smartphones, and a new analysis suggests they have a long history. Researchers have found that some hominins started developing more dexterous thumbs about 2 million years ago, which could have allowed them to exploit more resources, eventually leading to the emergence of human culture.

Katerina Harvati at the University of Tübingen in Germany and her colleagues looked at thumb efficiency across different fossil human species. The researchers looked at the shape of thumb bones and soft tissue, which is occasionally preserved. They also created 3D meshes of thumb samples and calculated their torque.

“Levels of dexterity very similar to what we see in modern humans were already present 2 million years ago,” says Harvati.

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Previous research has suggested that Australopithecus, an earlier genus of hominin, may have been the earliest toolmakers, but the researchers found these fossils lacked the same dexterity found in Neanderthals and Homo naledi.

The researchers suggest that Australopithecus might have been capable of using tools without being adapted for it, whereas the Homo genus developed dexterous thumbs and became adapted for more efficient tool making.

“Regardless of whether stone tool use started before the genus Homo, it’s only after 2 million years ago that stone tool use might have been more efficient,” says team member Fotios Alexandros Karakostis, also at the University of Tübingen. “Therefore, this increased efficiency is likely the factor that led to the gradual emergence of human culture rather than stone tool use itself.”

“All Homo share a common morphology that allows for more dexterity than what came before. And that is brought into light and well supported by this multidisciplinary approach,” says Sandra Martelli at University College London.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2020.12.041

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