On July 26th, 2015 we learned about

Your opposable thumb is sooo five million years ago…

Given our linear relationship with time, it’s easy to think of evolution as an example of progress towards a goal. When coupled with the idea that homo sapiens are a fairly young species, we often get caught up in the notion that we’re the newest and best iteration of life on Earth. That’s not how evolution works, of course, as what’s really happening is a series of changes to better fit ecological circumstances. This is demonstrated nicely by recent study of human hands that show that they’re not actually the latest and greatest in our family tree, but that doesn’t mean they’re at all obsolete.

The study in question looked at thumbs in a few ape and human ancestors. When compared to finger length, longer thumb bones result in opposable thumbs, such as on humans and gorillas. Researches wanted to see when these proportions first evolved in our ancestors, and how they compared to modern animals, especially our closest genetic relative, the chimpanzee.

Classic thumb vs. new thumb

Somewhat surprisingly, our long thumbs were not final revision of primate hands. Both Ardipithecus ramidus and Australopithecus sediba, from 5.6 million and 2 million years ago, respectively, had thumb bones in similar proportion to ours. Instead, the most recent changes to hand-to-finger ratios were found in chimpanzees, who now have much longer fingers to help them grasp tree limbs and move quickly through trees.

This information requires some reshuffling of our origins. Rather than humans splitting from chimps in the trees to move to the ground, our common ancestor may have already been living on the ground like gorillas do now. Chimps would have then moved back into the trees after that. It may also help explain some questions about our early tool use, where production and use of certain tools would have required opposable thumbs that may have been available earlier than previously believed.

Source: Human Hands More Primitive than Chimp Hands by Jennifer Viegas, Endangered Species

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