Why are 90% of humans right-handed? New research delves into the mystery of handedness.

The Deep Mystery of Handedness Linked to "Walking" and "Brain Evolution"

For humans, using the right hand is incredibly routine. Holding chopsticks, gripping a pen, operating a smartphone, turning a doorknob—many tools and actions in society are designed with right-handedness in mind. Of course, there are left-handed people, but globally, the majority of humans are considered right-handed.

This fact is not merely a matter of lifestyle habits. Rather, it has been a longstanding puzzle in evolutionary biology. This is because, unlike humans, other primates do not exhibit such a strong "collective right-hand dominance."

There are animals that prefer using either their right or left hand on an individual basis. Chimpanzees, gorillas, and orangutans have individuals that frequently use a specific hand. However, when looking at the species as a whole, the extreme bias of "almost all being right-handed" seems to be unique to humans.

So, when and why did humans become so biased towards the right hand?

A new study led by Oxford University, published in PLOS Biology in 2026, ties the answer to two major themes in human evolution: "bipedalism" and "brain expansion."

The research team collected data from 2,025 individuals across 41 species of monkeys and apes, statistically testing various hypotheses related to hand usage. They compared factors previously thought to influence the evolution of handedness, such as tool use, diet, habitat, body size, sociality, brain size, and modes of movement.

The results revealed something intriguing: humans appear distinctly abnormal when viewed against the patterns of other primates. In other words, only humans are excessively biased towards the right hand.

However, when factors such as "brain size" and "the relative length of arms and legs" are considered, the abnormality of humans disappears. The arm-to-leg ratio is an important indicator of adaptation to bipedalism. This suggests that the tendency for right-handedness in humans can be explained within the evolutionary flow when considering the upright walking body and expanded brain.

What makes this study interesting is that it does not treat the question of "why right-handedness emerged" as merely a matter of the hands.

Hands were also organs for walking. When our distant ancestors heavily relied on quadrupedalism and arboreal life, the forelimbs were used for movement—grasping branches, supporting the body, moving across the ground. Hands were not free.

However, as bipedalism progressed, hands were freed from the role of movement. Consequently, new uses such as carrying, processing, throwing, grasping, and fine manipulation became important. Hands transformed from "organs for walking" to "organs for manipulating the world."

However, bipedalism alone did not complete the strong right-handed tendency we see today. The research team suggests a two-stage story.

In the first stage, bipedalism freed the hands, strengthening the tendency to use one hand more specialized than the other. In the second stage, with the emergence of the genus Homo, the brain grew larger, and functional differentiation within the brain developed, meaning the left and right hemispheres took on different roles. This possibly led to a stronger right-hand dominance spreading throughout the population.

This hypothesis also connects to estimates of fossil humans.

Using the same model, the research team estimated the degree of right-hand dominance in extinct human ancestors. In early Ardipithecus and Australopithecus, the bias towards the right was relatively weak, similar to modern large apes.

However, in the lineage of Homo, such as Homo ergaster, Homo erectus, and Neanderthals, right-hand dominance becomes more pronounced. This tendency is strongest in modern humans, Homo sapiens.

On the other hand, there are exceptions, such as Homo floresiensis, the so-called "Hobbit humans" discovered on the island of Flores in Indonesia. This species had a small brain and may have been adapted not only to complete terrestrial bipedalism but also to climbing. The research team's estimate suggests that the right-hand dominance of Homo floresiensis was quite weak.

This aligns with the current hypothesis. If the brain was small and the mode of movement retained some arboreal characteristics, it would not be surprising for there to be less strong right-hand dominance than in modern humans.

In other words, right-handedness might be a byproduct of "human-ness."

We began to walk upright. Our hands became free. Our brains grew larger. We made tools, built cultures, and developed language. Somewhere in that process, the bias towards using the right hand intensified and stabilized across generations.

Of course, this study does not claim to have completely solved the reason for right-handedness. Rather, it should be seen as presenting a new framework for organizing the issue. Why do a certain number of left-handed people remain? To what extent have culture and education reinforced right-handed dominance? How much common evolutionary principle is there between animal lateralization and human handedness? These questions remain.

There has been a lot of reaction to this point on social media.

In the science community on Reddit, there were comments pointing out that "animals also have lateral biases." For example, it was noted that some species, like parrots and kangaroos, are known to prefer the left side. This suggests a perspective that human right-handedness should not be overly singled out but compared with the "lateralization" across the animal kingdom.

On the other hand, there was a more measured interpretation: "This study explains not so much why it's the right hand, but why the bias towards one side is so strong in humans." This is a very important point. The core of this study is not simply the "reason the right was chosen," but "why the bias in handedness became extremely strong in humans."

There was also a reaction questioning, "Isn't it cultural influence?" Indeed, there is a history of right-handedness being the standard in human society. Tools, writing, etiquette, school education, and many environments assume right-hand use. On social media, multiple accounts were shared of parents or grandparents who were left-handed being corrected to use their right hand in school.

This suggests the possibility that evolutionary explanations and cultural explanations overlap rather than conflict. There may be a biological tendency for right-hand dominance, which society and culture have further reinforced.

Especially in 20th-century education, there were cases worldwide where children writing with their left hand were forced to use their right. For left-handed people, the fact that everyday tools like scissors, desks, mice, can openers, and musical instruments are made with right-handedness in mind remains a small inconvenience. Left-handed users on social media shared their experiences of "adapting within a right-handed society."

This discussion is very compelling as a scientific article. This is because "handedness" is so familiar yet connects to many themes such as the brain, body, evolution, culture, education, discrimination, and tool design.

The majority being right-handed is not just a statistic. It is a history of human use of the body and a cultural history of which hand society has deemed "normal."

It's important to note that this is not a discussion of right-handedness being "evolved" and left-handedness being "unevolved." On social media, there were joking responses like "Is left-handedness more evolved, or the opposite?" but scientifically, this is not a matter of superiority or inferiority.

Handedness is a phenomenon where the tendencies of the entire species and individual differences overlap. While right-handedness is more common in humanity as a whole, the continued existence of a certain percentage of left-handed people remains an evolutionary mystery to be solved. There is a hypothesis that left-handedness may introduce unpredictability in sports or interpersonal competition, and multiple factors are thought to be involved in brain lateralization and developmental processes.

What this study suggests is that behind the everyday occurrence of right-handedness, there may be bodily changes on a scale of millions of years.

We grasp the world with our hands. But those hands became free because we stood on our feet and began to walk. Walking freed our hands, which led to the creation of tools, and using tools further developed our brains and culture. In this light, the image of humanity biased towards the right hand seems not merely coincidental but an evolutionary trace marked by an upright body and an expanded brain.

When scrolling a smartphone with the right hand, running a pen with the right hand, or when left-handed people feel slight inconvenience with right-handed tools, the shadow of our distant ancestors' way of walking might be cast.

Handedness is not just about the hands.

It is a small yet significant gateway that touches on the history of humanity standing up, walking, thinking, making tools, and building societies.

Source URL

Phys.org. Introducing research led by Oxford University, it discusses the possibility that bipedalism and brain expansion explain human right-hand dominance, using data from 41 species and 2,025 primate individuals.
https://phys.org/news/2026-05-why-is-almost-everyone-right.html

Oxford University official news. Refer to confirm the overview of the study "Bipedalism and brain expansion explain human handedness," the significance of the research, and explanations regarding bipedalism and brain expansion.
https://www.ox.ac.uk/news/2026-05-15-why-is-almost-everyone-right-handed-the-answer-may-lie-in-how-we-learned-to-walk

Oxford University Research Archive paper information. Refer to confirm the paper title, authors, PLOS Biology publication details, comparative analysis of 41 species and 2,025 individuals, and the abstract explaining that brain capacity and limb ratio account for human right-hand dominance.
https://ora.ox.ac.uk/objects/uuid%3A44b7f31d-59ff-4d4f-a5c9-f0b5e3ee28df

Reddit r/science post and comments. Refer to discussions on animal lateralization, cultural influences, experiences of left-handed correction, and interpretations of the research content as social media reactions.
https://www.reddit.com/r/science/comments/1te1th9/about_90_of_people_across_every_human_culture/

LinkedIn post on Phys.org. Refer to confirm the introduction and reaction count on social media.
https://www.linkedin.com/posts/phys-org_why-is-almost-everyone-right-handed-the-activity-7461106162579652608-zd0_

Related posts on X. Refer to confirm sharing status by Phys.org, researchers, and paleoanthropologists.
https://x.com/physorg_com/status/2055371848305541320
https://x.com/ThomasPuschel/status/2055297613017014274
https://x.com/ChrisStringer65/status/2049141600710713740