Thumbs and Innovation – What if Humans Lacked Opposable Thumbs?

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Picture credit:National Geographic

My son’s 7th Grade project asked the question above as a scientific inquiry ! IAI jumped at the chance to chime in…They are called opposable (Encyclopedia Britannica details here) because the thumb can be moved around to touch the other fingers, which gives people the ability to grasp things. Most primates (humans, apes, and Old World monkeys) and some other animals have opposable thumbs.

  • All inventions since the Stone Age including spears, rope, hammers, etc. would be different without thumbs to grip them so might have evolved more slowly,
  • Gibbons, our most distant Great Ape cousins, lack opposable thumbs because they’re get in the way of swinging through the forest canopy,
  • We need thumbs to hold/throw/manipulate objects–all prerequisites to making and employing weapons that can act at a distance (rocks, throwing spears, atlatls, bows/arrows),
  • There would be less incentive for humans to be upright since we be inclined to be four legged runners (using knuckles on the front two arms). Upright bipedal walking in hominoids allowed the hands to be freed for other things such as tool/weapon use.
  • Some scientists speculate that human language would not have developed without the evolutionary effect of the human brain making the effort to invent and learn new uses for the hands,
  • Without thumbs, we could not punch each other (see below),

 Sometimes, investigators and scientists turn the question around and ask, “Who has opposable thumbs?”

This video shows that Opossum thumbs are real ! (https://youtu.be/k51iPtwnvng)

Many animals, primates and others, also have some kind of opposable thumb or toes:

* Bornean Orangutan – opposable thumbs on all four hands. The interdigital grip gives them the ability to pick fruit.
* Gorillas – opposable on all four hands.
* Chimpanzees have opposable thumbs on all four hands.
* Lesser Apes have opposable thumbs on all four hands.
* Old World Monkeys, with some exceptions, such as the genera, Piliocolobus and Colobus.
* Cebids (New World primates of Central and South America) – some have opposable thumbs
* Koala – opposable toe on each Marsupial foot, plus two opposable digits on each hand, and unbearably cute unless you try to take its eucalyptus…
* Opossum – opposable thumb on rear feet and is it a “bear”?
* Giant Panda – Panda paws have five clawed fingers plus an extra bone that works like an opposable thumb. This “thumb” is not really a finger (like the human thumb is), but an extra-long sesamoid bone that works like a thumb and this bear adapted its diet to bamboo but is also carnivorous,
* Troodon – a birdlike dinosaur with partially opposable thumbs (and 10 amazing facts from Mental Floss – a site full of fun facts !), and
* Raccoon – a common mammal with thumbs, which are not opposables (but don’t ever let one get into your woods cabin!)

Picture Credit: AFP- Agencie France Presse

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The BBC reported recently that, the giant panda is no longer an endangered species, in part due to the efforts of the World Wildlife Fund and the Chinese embrace of the central China bear as its national mascot. With nearly 1900 adult Pandas living, the species is now “just” vulnerable according to an update to the International Union for Conservation of Nature (IUCN) Red List. However, with populations falling towards 2000, the eastern gorilla, the world’s largest primate, is now endangered.

Testing a hypothesis about fistfights with cadaver arms, Popular Science reported on the research of Utah State biologist David Carrier who “thinks the human hand’s uniqueness was shaped, in part, so we could punch each other in the face. Carrier introduced this off-beat hypothesis a few years ago, to much controversy.” In the Journal of Experimental Biology, Carrier tested the “pugilism hypothesis of hominin hand evolution” by employing the disembodied arms of cadavers to demonstrate that clenching your fist and wrapping your thumb around your fingers reduces your chances of breaking your hand when you punch something. Other studies from the Journal of Anatomy and other journals suggest the human hand was used initially for throwing and clubbing once the humanoid learned a two legged “gait”. As PopSci points out, “Human hands are shorter and boxier than our ape relatives, and our thumbs are proportionally longer in relation to the other fingers. This gives us the unique ability to not only manipulate tools with fine precision, but also form a fist. We’re the only animals that can. We are the only animals with fists.”

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