By J. DeVoy
Humans’ opposable thumbs are crucial to a range of functions needed to grapple with and manipulate materials to build advanced shelters, tools, and other devices. But our hands could have developed in any number of ways while retaining opposing thumbs – why is the human hand proportioned the way it is?
Answer: To punch people.
Prof. David Carrier at the University of Utah has been testing this hypothesis and postulates that:
“there are several possible hand shapes that would have allowed greater dexterity, making it less clear why we ended up with the hands we have. But only one hand shape lets us make a fist with a thumb as buttress.” (source)
More information at the link.