Those hands were made for punchin’. Well, that’s the conclusion of newly published research, which suggests that our hands didn’t evolve solely to improve manual dexterity, but also so that males could engage in games of fisticuffs over females. That would suggest, controversially, that the human fist is not just an added bonus of natural selection for dexterity, but in part due to the advantages it bestows in aggressive behavior, namely fighting.
“The standard argument is that the hand proportions we have are all about manual dexterity, like tool use,” lead researcher David Carrier from the University of Utah told IFLScience. “There’s no arguing with that. But what we are saying is that, in addition, there may have been selection on specific proportions that make a clenched fist possible.”
You’ve probably not thought about it before, but the human hand is somewhat paradoxical. Many of its uses, from preparing food to crafting tools, require delicate features capable of fine manipulation. But we also use our fragile hands to fight over things, particularly females. This apparent incompatibility has been suggested to be the result of dual specialization for both dexterity and, contentiously, punching.
“Except for bonobos, great apes are a relatively violent group,” said Carrier. “Their aggression is mostly about male-male competition for females. But if we look at humans, at some point our species became very much committed to investment by the father in offspring. So violence and aggression also became about fighting and protecting just a handful of offspring we invest our entire lifetime raising.”
This could, perhaps, partly explain some of the unique features of the human hand that allow the formation of a clenched fist. Compared to other apes, humans have shorter palms and fingers, but longer, more robust thumbs. Chimps, for example, have extended fingers that are more like those of our common ancestor, which are associated with tree climbing.
Since male-male competition is so important in great ape mating systems, the researchers hypothesize that a clenched fist protects the hand bones from injury by reducing strain sustained when striking. More specifically, they propose it redirects the energy in a punch through the thumb to a certain extent so that the palm bones experience less load. To test this out, the team turned to cadavers. Perhaps an unconventional approach to look into our evolutionary past, but Carrier argues you can only go so far back using historical and archeological records before they get “too sketchy.”
To measure bone deformation during striking, the team attached strain gauges directly to the hand bones of the donated cadavers – an invasive procedure, hence live subjects were not appropriate. They then attached fishing lines to the tendons so that the position of the hand could be manipulated, forming tightly clenched (buttressed) or loose (unbuttressed) fists. The hands were then placed in an apparatus and swung towards a force-detecting dumbbell.
As reported in the Journal of Experimental Biology, they found that strains were much higher in strikes where the hand was unbuttressed or relaxed in a slapping position when compared with clenched fists. Buttressed fists, they report, allow for safe striking with 55% more force than unbuttressed fists. These findings, they argue, could suggest our hand proportions evolved not only to improve dexterity, but to allow the use of hands as a weapon during fighting. This is supported by the differences observed between male and female hands, which are one of our more sexually dimorphic features.
The work does not come without criticism, such as a lack of convincing evidence for historic fist fighting, but Carrier argues his case and believes that aggression played a key role in our evolution.