About 90% of people on the planet are right-handed, and that proportion is remarkably stable across countries, cultures and eras. Scientists have long understood that such a pattern could not be random, but they did not have a precise explanation. Now researchers from Oxford and Reading, after analyzing data on 2,025 primates from 41 species, have proposed a convincing account of where human right-handedness came from.
It turns out that humans differ significantly from their closest relatives in this respect. Chimpanzees, gorillas and orangutans can also have a preferred hand, but no species shows the same mass-scale and enduring preference for the right hand as Homo sapiens. The key to the puzzle was found in two factors: brain size and locomotion. When the researchers took these parameters into account, their models explained human right-handedness almost perfectly.
Bipedalism appears to have played the main role. Once our ancestors finally stood on two legs, their hands were freed from locomotion and could focus on more delicate tasks, from making tools to manipulating objects in complex ways. And if you are learning to use a stone axe, it is more convenient to do so with one leading hand rather than passing it back and forth with every swing.
Brain growth was also important. The study showed that as the genus Homo evolved, the tendency toward right-handedness became stronger: it was weaker in Homo erectus, intermediate in Neanderthals, and at its strongest in modern humans. That means the habit of picking up a spoon or a computer mouse with the right hand may be a legacy of events that began millions of years ago, when our ancestors were just learning to walk steadily on two legs.
