From writing and eating to throwing and building tools, humans overwhelmingly favor the right hand in everyday life. Across cultures and continents, nearly 90% of people are right-handed, a level of dominance rarely seen elsewhere in the animal kingdom. Currently, a notable new study indicates that the answer may come down to two defining changes in human evolution: upright walking and the swift expansion of the brain.
Oxford researchers analyze more than 2,000 primates
The study was headed by Dr. Thomas A. Püschel and Rachel M. Hurwitz from Oxford’s School of Anthropology and Museum Ethnography, along with Professor Chris Venditti from the University of Reading.
Published in PLOS Biology , the research analyzed behavioral data from 2,025 monkeys and apes belonging to 41 various primate species. With advanced Bayesian statistical techniques, the scientists tested many significant theories connected to handedness. They looked at how factors like tool use, body size, habitat, diet, social structure, movement patterns, and brain development may have influenced hand preference throughout evolutionary history.
Humans stopped looking “unique” after two factors were added
At the beginning of the analysis, humans seemed to be dramatically different from all other primates because of their extreme right-hand dominance.
However, scientists noticed something unexpected once they introduced two extra measurements into their models: brain volume and the proportion between arm length and leg length, an important sign of upright movement.
After accounting for those traits, humans no longer appeared like a biological exception. The results indicate that the combination of bipedal movement and expanded brains may explain why humans slowly developed such a powerful tendency toward right-hand use.
How walking upright may have changed human behavior
As per the researchers, the shift toward walking on two legs likely has a major role in reshaping hand use. Earlier primates relied heavily on their arms for climbing and movement. But as ancient human ancestors became increasingly upright, their hands were freed from locomotion and could specialize in other activities.
Researchers believe this created new evolutionary pressures favoring more precise and asymmetric hand movements, mainly for carrying objects, manipulating tools, and doing coordinated actions.
Bigger brains may have strengthened right-handedness
The study indicates that brain expansion later amplified this imbalance. As human brains became larger and more complex, specific functions increasingly specialized in one hemisphere of the brain. Researchers believe this neurological specialization may have strengthened right-hand dominance over time, especially in species that belong to the genus Homo .
The team estimates that early ancestors like Ardipithecus and Australopithecus probably featured only mild hand preferences, similar to modern great apes. But later species that include Homo ergaster , Homo erectus , and Neanderthals likely developed much stronger right-hand tendencies, eventually resulting in the overwhelming dominance spotted in modern humans.
The curious case of the “hobbit” species
One extinct human relative stood apart from this evolutionary pattern.
Researchers forecast that Homo floresiensis often termed the “hobbit” species because of its unusually small body size likely had a much weaker preference for the right hand. As per the team, this fits with the species’ anatomy. Homo floresiensis possessed a relatively small brain and retained physical adaptations connected with both climbing and upright walking, rather than being completely specialized for life on two legs.
Scientists propose a two-stage evolutionary process
The researchers believe human handedness may have evolved through two major stages.
First, upright movement liberated the hands from locomotion-related responsibilities, encouraging more specialized use of one hand. Later, increasing brain complexity and neurological specialization intensified that preference, producing the strong right-hand dominance now widespread among humans globally.
Dr. Thomas A. Püschel described: “This is the first study to test several of the major hypotheses for human handedness in a single framework. Our results suggest it is probably tied to some of the key features that make us human, especially walking upright and the evolution of larger brains. By looking across many primate species, we can begin to understand which aspects of handedness are ancient and shared, and which are uniquely human.”
Questions scientists still cannot answer
Despite the latest discoveries, researchers say several puzzles remain unanswered.
Scientists still do not completely understand why left-handedness survived throughout human evolution or how culture and societal traditions may have strengthened right-hand preference across generations. The team also believes similar limb preferences observed in animals such as parrots and kangaroos could uncover deeper evolutionary trends shared among very different species.
Source : ScienceDaily
FAQs:
Q1. Why are most humans right-handed?
Scientists believe upright walking and larger brain development may have strengthened right-hand dominance over millions of years. These evolutionary changes likely encouraged more specialized hand use.
Q2. How many people are right-handed?
Around 90% of humans worldwide prefer using their right hand for most daily activities. This pattern appears across nearly all cultures.
