The rise of right-handedness
Study explores why trait is so prevalent in people, cultures
The innumerable differences between people are what make humanity one of nature's most compelling and spellbinding tapestries. But why do the vast majority of us share certain characteristics, such as right-handedness, over others?
Researchers from the United Kingdom think two uniquely human traits — bipedalism (the use of two rear limbs, or legs) and enlarged brains — may be responsible for a specieswide preference for favoring our right hand, according to a study published April 27 in the journal PLOS Biology.
The study, authored by Dr. Thomas A. Püschel and Rachel M. Hurwitz at Oxford's School of Anthropology and Museum Ethnography, as well as Professor Chris Venditti at the University of Reading, says "the predominance of right-handedness in humans is a robust cross-cultural phenomenon, and no left-dominant human society has been documented, making it unlikely that culture alone can account for the evolutionary trajectory of handedness in our species."
Here's what you should know about the dominance of right-handedness.
Comparison of species
To find out why so many of us are right-handed, the researchers collected data from 2,025 individuals across 41 species of monkeys and apes. Accounting for the species' evolutionary relationships, they analyzed the evolution of handedness through the lens of prevailing hypotheses, including tool use, diet, habitat, body mass, social organization, brain size and locomotion.
What they found is that humans don't fit neatly into the same patterns that explained the other species' handedness.
"This is the first study to test several of the major hypotheses for human handedness in a single framework," Püschel said in a statement. "By looking across many primate species, we can begin to understand which aspects of handedness are ancient and shared, and which are uniquely human."
Evolution's role
According to Püschel and his colleagues, when we evolved to walk upright, we also began using our hands for a host of new purposes.
"The initial adoption of an upright gait freed the upper limbs, creating novel opportunities for tool use, gestural communication and other fine motor behaviors in which lateralization would have conferred performance advantages," the researchers wrote.
Because bipedalism paved the way for more sophisticated behaviors, it was effectively the first step on humans' journey to right-handedness. Our larger brains grew and reorganized accordingly, solidifying the rightward bias seen today, according to the study.
"In humans," the researchers wrote, "the evolution of bipedalism and the subsequent freeing of the hands may have intensified selective pressures for stronger hand preferences."
Püschel, Hurwitz and Venditti noted several other lines of inquiry that their research opens, including what role culture played in normalizing right-hand dominance, why some people are still left-handed today, and whether similar patterns of limb preference seen in other species "point to a deeper, convergent story across the wider animal kingdom."
