The dominance of right-handedness in the human population has puzzled scientists for years. There are plenty of reasons why having a dominant hand is a good idea. For example, it allows the specialization between the two halves of the brain, which may lead to enhanced cognitive abilities; one side is free to do whatever it wants while the other focuses a bit on the Doritos you’re eating. But individual advantages to having a dominant hand doesn’t explain why so many righties exist.
Believe it or not, hand dominance is not completely a genetic trait. Identical twins that share the exact same DNA have developed different handedness on occasion. So there are both genetic and environmental factors at work. And going back throughout human history, societies have always been dominated by righties, with rates ranging from 97% to 74%.
So what gives?
According to new research from Northwestern University, it’s the level of cooperation versus competitiveness within a society that drives it develop a preferred hand dominance. Though the paper doesn’t strictly give exact reasons for the phenomenon, it does create a working mathematical model that accurately predicts the handedness ratio in different groups of people.
According to authors Daniel M. Abrams and Mark J. Panaggio, a disparity in hand dominance occurs when a society is extremely cooperative. As humans evolved to use tools, those tools would naturally be more useful for a person who shared the same hand dominance as the person who created it. And because people were apt to share tools and cooperate to build a society, pressures were slowly exerted to drive the population to share a hand dominance.
Of course, that doesn’t explain why righties won out. For all we know, it could just have easily been the lefties.
To further test their hypothesis and mathematical model, the duo looked to other groups to see how well it could predict the level of lefties. Animals are naturally difficult to study, as it’s tough to gauge their levels of cooperation as well as which paw they prefer. So they looked at several subgroups of humans – elite athletes.
Some sports have a high degree of competitiveness where being different than the normal would give an advantage. For example, lefties have long been popular in baseball where it is an advantage in hitting as well as – in a few positions – fielding. Boxers often can get mixed up by facing a southpaw. Just ask Apollo Creed.
By estimating the amount of competitiveness versus cooperation and how much of an advantage being different from the norm would give a player, Abrams and Panaggio accurately predicted the ratio of righties to lefties in several major sports. More than 50 percent of the top baseball players throughout history have been lefties, and well more than the national average of 10 percent have been lefties in boxing, hockey, fencing and table tennis.
On the other hand, in sports where specialized equipment is key and players don’t actually square off directly against each other, lefties were quite rare. For example, golf. Most clubs are made for righties and being different from the field gives no advantages. Thus, the number of successful PGA golfers dips way down to four percent.
Obviously, there are many caveats to this line of research. The measures of competitiveness, cooperation and physical edge are difficult to nail down empirically. But still, the overall concept seems to work pretty well, giving credence to the idea that cooperation has driven humans to use the same kind of scissors.
But as far as I can figure, the world’s scissors could have just as easily been lefties.