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New Discovery Hands Human Evolution a Challenge

By Fazale Rana - August 13, 2015
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The human hand is remarkable. It permits humans to manufacture and use a wide range of tools, distinguishing us from animals and undoubtedly contributing to our success as a species.

One of the unique features of the human hand is our lengthy thumbs. In contrast, chimpanzees have much shorter thumbs, strikingly disproportionate to their long fingers.

In spite of the human hand’s elegant design, many evolutionary biologists believe that it was shaped by an evolutionary history. They believe a knuckle-walking ape-like creature evolved the capacity for bipedalism, freeing the hands, which in turn evolved to become more dexterous. While long fingers and a short thumb are ideal for knuckle walking, they have limited utility for tool making. Presumably, strong selective pressure influenced the thumb and finger proportions (along with it the dexterity of the hand) as hominids began to use tools.

New work, however, undermines this standard evolutionary story.1 Researchers from George Washington and Stony Brook universities recently presented data that suggests that the last common ancestor of humans and chimps possessed a human-like hand, not a chimp-like hand. In other words, the human hand is primitive and the chimpanzee hand represents an evolutionarily advanced state.

These researchers reached this conclusion after doing a careful comparison of human hand proportions with those of monkeys, apes, and the fossil remains of early hominid species and by using this hand data to build an evolutionary tree. They discovered that the hand proportions of monkeys and apes are quite diverse, and the human hand isn’t necessarily that unique. The evolutionary tree they built indicated that human and gorilla hands are very similar, suggesting an ancestral state. On the other hand (no pun intended), chimps and orangutans display similar hand proportions, reflecting convergent evolution.

This work has far-reaching implications when humanity’s origin is viewed from an evolutionary vantage point. Even though the standard evolutionary model regards the last common ancestor of humans and chimps as chimp-like, this latest study indicates that this view is incorrect. That is, the evolutionary ancestor of humans wasn’t a knuckle-walking ape-like creature at all. In fact, it’s not clear what this creature looked like.

Perhaps even more significant is the recognition that the human hand didn’t evolve over time to be better adapted for tool use. It seemingly was capable of doing so all along. With this latest insight, evolutionary biologists are left without an explanation for the origin of the remarkable manual dexterity of humans and the genesis of tool usage.

Time and time again the standard account of human evolution turns out to be incorrect. In this particular instance, the idea that the human hand evolved under selective pressure associated with development and use of increasingly sophisticated tools has been a mainstay of human evolution for nearly four decades. And yet, a single study overturns this idea. This latest work begs the question: How secure is any idea associated with human evolution?

If you want to read about another mainstay idea in human evolution that has been cast aside, check out this article: “The Leap to Two Feet: The Sudden Appearance of Bipedalism.”

Endnotes
  1. Sergio Almécija, Jeroen B. Smaers, and William L. Jungers, “The Evolution of Human and Ape Hand Proportions,” Nature Communications 6 (July 2015): id. 7717, doi:10.1038/ncomms8717.

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