Humans are really good at using tools with our elbows

Humans can use tools with many body parts, from feet to elbows. This suggests the brain bits behind dexterity aren’t restricted to our hands.


Our hands are pretty good at using tools, probably because they’ve been adapting to do so for more than 3 million years1. But it turns out they aren’t the only body part we can use tools well with. We can also use our elbows, feet, and non-dominant hands quite well2.

Now, that doesn’t mean all these weird body parts also evolved for tool use. Humans, it seems, are just very good at generalising our motor skills. Once we’ve figured out how to use a hammer to hit a nail, it doesn’t take much effort to apply those skills to other body parts2.

This ability – called poly-dexterity – isn’t just some weird quirk of our brain. Instead, its discoverers suggest it’s a sign that the bits of the brain responsible for tool use evolved before our hands. Hence why the former isn’t limited to just the latter2.

If true, this could dramatically change our understanding of the order things happened during human evolution.

Experiments with elbows

Osiurak et al. found a paradox.

See, it seems that our fancy hands were evolving ~3 million years ago, back our brain was still chimp-like. So when the brain began to catch up, there was already some specialised equipment at the end of our arms. Thus, many people think that dexterity and our hands are thoroughly intertwined in our brain1.

Early hominin hands showing key similarities with ours, despite predating much of our brain’s evolution1

And yet, we see people born without arms able of performing quite deft actions. How could this be if our dexterity is stuck in our hands2?

This led Osiurak et al. to speculate that maybe dexterity and hands weren’t as closely linked as many people thought. So they did what any good scientists do when they come up with some speculation: they set out to test it.

Their test was deceptively simple. It essentially consisted of taping tools to different body parts, like our elbows. If people really were poly-dexterous as they thought, they should have little trouble adapting to these new circumstances. On the other hand, if hands are really crucial for dexterity they should just flop incapably like a Magikarp in battle.

One set of experiments, with hammers!2

As both the title and summary at the start of this post gives away, their results supported their hypothesis. It seems that people poly-dextrous, capable of adapting to use just about any body part you can tape a tool too.

Whilst discovering this secret superpower is cool and all, there’s more significance to this discovery. The fact that dexterity isn’t just limited to our hands has some important implications for our evolution.

Poly-dexterity and human evolution

The obvious implication that we can use tools with our elbows is that tool use isn’t as intertwined with our hands as we thought. So whilst we may start seeing hands adapting to tool use ~3 million years ago, tool use may have been happening for a long time previously.

This makes sense. After all, many apes use tools; so it’s likely our early ancestors were too. Plus, why would our hand start to adapt to tool use if we weren’t already using tools? Things don’t evolve on the off chance they might become useful later.

A bonobo making stone tools like a boss, despite having different hands

But this also raises a key question. If we were using tools for a long time, why did our hands only start adapting to this ~3 million years ago? Something changed in our evolution to free up our hands for tool use. Maybe it was the fact we were using them less to climb, maybe tool use suddenly became more important, or perhaps we just got evolutionarily lucky1.

So this research hands us more questions than it solves. But now we know that they’re out there, we can start reaching out for answers. Who knows what we might grab onto? And how many more hand-based puns I can squeeze into the next post on the subject?

References

  1. Kivell, T.L., 2015. Evidence in hand: recent discoveries and the early evolution of human manual manipulation. Phil. Trans. R. Soc. B370(1682), p.20150105.
  2. Osiurak, F., Lesourd, M., Delporte, L. and Rossetti, Y., 2018. Tool Use and Generalized Motor Programs: We All Are Natural Born Poly-Dexters. Scientific reports8(1), p.10429.

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Humans are really good at using tools with our elbows

by Adam Benton
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