One of the greatest mysteries in human evolution has long puzzled scientists. That is, why are humans so overwhelmingly right-handed? Approximately 90% of people across cultures prefer to use their right hand, a level of dominance not found in other primates. Researchers have spent decades studying the brain, genetics, and development behind handedness, but it remains unclear why humans became so right-handed.
Now, a new study led by researchers at the University of Oxford points to two major evolutionary milestones: walking upright and the dramatic growth of the human brain.
This study PLOS Biologywas carried out by Dr. Thomas A. Puchel and Dr. Rachel M. Hurwitz from the School of Anthropology and Museum Ethnology at the University of Oxford, and Professor Chris Venditti from the University of Reading. The research team analyzed data from 2,025 monkeys and apes representing 41 different primate species.
The researchers tested several leading theories about the origin of handedness using Bayesian modeling, which takes into account how species are evolutionarily related. They investigated factors such as tool use, diet, habitat, body size, social structure, brain size, and movement patterns.
Walking upright and brain enlargement
Humans initially set themselves apart from other primates in analysis. But things changed when researchers added two important features to the model. It is the ratio of brain size to arm length to leg length that is commonly used as a marker of bipedalism.
Given those characteristics, humans no longer seem to be such an evolutionary anomaly. The findings suggest that the combination of upright walking and large brains may explain why humans have an unusually strong preference for the right hand.
The study also allowed researchers to estimate the handedness of extinct human ancestors. Their results suggest that early humans were Ardipithecus and Australopithecus It probably showed only a mild right-handed preference, similar to that seen in modern great apes today.
This pattern appears to be greatly strengthened by the appearance of this genus. homo. contains seeds homo ergaster, the man stood upAnd Neanderthals probably developed an increasing preference for the right hand, eventually leading to the extreme advantage seen in modern humans.
A strange incident involving the hobbit race
One species stands out from this trend. homo floresiensisthe small-bodied species is often given the nickname “hobbit” because of its small size. The researchers predicted that this type of right-sided bias would be much weaker.
The researchers say this finding fits into a broader pattern of evolution. homo floresiensis Their brains were relatively small, and they retained physical adaptations for both tree climbing and upright walking, rather than being fully specialized for bipedal locomotion.
Researchers believe the evidence points to a two-step evolutionary process. First, walking upright freed the hands from movement, creating new pressures favoring more specialized and asymmetrical hand usage. Later, as the human brain became larger and more complex, the preference for the right hand became even stronger and more widespread.
Dr. Thomas A. Püschel, Wendy James Associate Professor of Evolutionary Anthropology at the University of Oxford, said: “This is the first study to test several major hypotheses about human handedness in a single framework. Our results suggest that this is probably what makes us human. “By looking at many primate species, we can begin to understand which aspects of handedness have been common since ancient times, and which aspects are still inherited.” It’s unique to humans. ”
Why do lefties still exist?
This study also raises new questions for future research. Scientists still don’t fully understand why left-handedness has persisted throughout human evolution, or how human cultures have reinforced right-handedness over time.
Researchers are also interested in whether similar limb preferences found in animals such as parrots and kangaroos may indicate deeper evolutionary patterns common to disparate species.
