Why Do Humans Have Thumbs?

Of all the motions the hand can perform, perhaps none is so distinctively human as a punch in the nose. Other animals bite, claw, butt or stomp one another, but only the species that includes Muhammad Ali folds its hands into a fist to perform the quintessential act of intra-species male-on-male aggression.

David Carrier, an evolutionary biologist at the University of Utah, believes our key advantage is the dexterity and configuration of our thumb, which folds over the second and third fingers as a buttress, concentrating the striking power and protecting the delicate hand bones. (Crucially, male index fingers are short relative to the ring fingers, so they fit snugly behind the bulge of muscle at the thumb’s base; in women, the second and fourth fingers are typically the same length.)

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