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Is the non-dominant hand vital to the evolution of the thumb?

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From ScienceDaily:

It is well known that one of the main distinctive features between humans and our closest evolutionary cousins, the great apes, is the morphology and manipulative capabilities of their hands. Key to this is the substantially larger, stronger and more robust thumb displayed by humans with such a thumb allowing humans to forcefully and yet dexterously manipulate objects within the hand, a trait first thought to have evolved alongside the earliest stone tool use between 2.6 — 1.4 million years ago.

But most research has focused on the dominant hand.

In the research, PhD student Alastair Key and his research associate Christopher Dunmore, of the University’s School of Anthropology and Conservation, showed that the production of stone tools requires the thumb on the non-dominant hand to be significantly stronger and more robust than the fingers.

Their results, published in the Journal of Human Evolution, demonstrated that the thumb on the non-dominant hand was not only required to exert and resist significantly more force than the fingers when manipulating stone cores, but that it was also recruited significantly more often. This means that our earliest stone tool producing ancestors were likely to have experienced similar recruitment levels, with those individuals displaying a stronger, more robust thumb being more capable stone tool producers and thus having an evolutionary advantage. More.

In principle, the idea is a good one, but note how Darwinspeak about “evolutionary advantage” intervenes at the end.

It is more likely that many left thumbs grew stronger when they were given much more exercise. If human survival had really depended on people who just happened to have strong left thumbs for no particular reason, most communities would not have survived. Whether one’s left thumb was strong would likely depend on whether one had to make tools.

Even so, this sounds much more plausible than many human evolution theories aired today that depend on the hand or parts thereof. As I wrote in Human origins: The war of trivial explanations:

Similarly, the human hand is simply a byproduct of changes to the shape of our feet. Or maybe not.Did stone tools really change human hands? Darwin speculated on this, which makes the idea canonical today. Curiously, while many claim that apes use and shape tools like humans, few speculate why doing so had no such dramatic effect on their hands.

We are told by others that fighting “may have” shaped the evolution of the human hand. One academic offers, “I think there is a lot of resistance, maybe more so among academics than people in general — resistance to the idea that, at some level humans are by nature aggressive animals.” Resistance? Really? Among academics and pundits, that is surely the conventional view!

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