The shape and dexterity of our hands enable us to write, paint, gesticulate and even take part in a fist fight. The general consensus is that the nimble human hand evolved as our ancient ancestors began using tools – but that might not be the whole story, according to a study published in the Journal of Human Evolution.
First things first. Human hands are very different from those of other primate species. (Though not necessarily any more evolved.) Our wrists are more flexible. Our joints are larger. Our thumbs are longer and more muscular but our fingers are shorter. These adaptions help us with tasks like building a fire, throwing spears at woolly mammoths and, of course, making and using tools.
Researchers at Chatham University, Pennsylvania, and the University of Kent, UK, believe that some tool behaviors are more essential to the evolution of the human hand than others. "Though archaeological evidence suggests that early hominins participated in a variety of tool behaviors, it is unlikely that all behaviors equally influenced modern human hand anatomy," they write in the study.
Of specific importance, they say, is weapon-making and our ancestors' taste for the juicy and calorie-rich substance found in bones, aka bone marrow.
To explore their hypothesis, the researchers recruited 39 volunteers to complete various neolithic-era tasks, like cracking a nut, wielding a handaxe, hammering flint with a stone, and hitting bones to extract bone marrow. While this was going on, the volunteers wore a glove-like contraption to monitor manual pressure distributions.
The results show that using a stone to crack open nuts involved the least manual pressure and, therefore, nutcracking in and of itself isn't a reason for us to evolve uniquely dextrous hands, Tracy Kivell, a professor in anthropology at the University of Kent said in a statement. After all, monkeys in Brazil and Panama have now technically entered the Stone Age.
Instead, it was using a hammerstone to collect marrow or make flakes of flint (to use as weapons) that required the most pressure. This, the researchers say, suggests these two behaviors had more of an influence on the anatomical and functional evolution of the human hand than the other 37 behaviors measured.
So, there you have it. While the evolution of the human hand is a long and complicated process that cannot be explained by one or two neolithic activities, munching on bone marrow and carving stone tools may have been two of the driving forces.