Why there are so few left-handed people: scientists have found a new evolutionary clue

A new study from Oxford University offers an evolutionary clue. The authors believe that mass human right-handedness could be linked to two key features of our evolution: the transition to walking on two legs and brain enlargement. The work is published in PLOS Biology.

Important: the study doesn't say that left-handedness is an outlier or a "bug." It's only about a statistical skew: why, at the level of humanity as a whole, there are far more right-handed people than left-handed people.

The details

Scientists have long tried to understand why humans differ so much from other primates in their hand preference. In monkeys and great apes, individuals may also use one hand more often, but the species as a whole usually doesn't have such a consistent rule: almost everyone is right-handed.

The authors of the new paper collected data on 2,025 individuals from 41 species of monkeys and great apes. They then tested different hypotheses: whether hand preference could be influenced by tool use, diet, habitat, body mass, social organisation, brain size and mode of locomotion.

At first, humans did appear to be an exception. No other primate showed such pronounced right-handedness at a population-wide level. But when the researchers added two factors to the model - brain size and the ratio of arm and leg lengths associated with upright walking - humans stopped looking like a "strange error" in the overall evolutionary picture.

The explanation goes like this: when human ancestors started walking on two legs, the hands were freed from a permanent role in locomotion. They could be used more often for precise actions - carrying objects, processing materials, making tools, communicating with gestures. In such a situation, the specialisation of one hand may have become increasingly useful.

Later, with the enlargement of the brain and the development of a more complex nervous system, this bias could have taken hold more strongly. According to the authors' theory, uprightness could have created the conditions for hand specialisation, and a larger brain could have reinforced and stabilised the preference for the right hand.

The researchers also tried to assess how right-handedness might have changed in ancient human relatives. According to their model, in early hominins like Ardipithecus and Australopithecus, the right-handed "skew" may have been weak, roughly the same as in modern great apes. With the appearance of the genus Homo, it became noticeably stronger, and in Homo sapiens it reached the modern level.

A separate exception is Homo floresiensis, known as the "hobbit" from Indonesia. For him, the model predicts a weaker preference for the right hand. The authors attribute this to a smaller brain size and a body structure that combined uprightness with climbing adaptations.

Why it matters

Right-handedness is a familiar thing that's easy to overlook. But from an evolutionary perspective, it's an unusual trait. People don't just often choose one hand: in almost all cultures, the majority choose to use their right hand.

A new study helps explain why this bias may have become so strong. It links the work of the hands not to a single cause - such as tools alone, or the brain alone - but to the broader history of the human body: we stood on two legs, freed up our hands, and got a brain that can increasingly distribute tasks between the sides of the body.

That said, the question is not definitively closed. The authors themselves note that important mysteries remain: what role culture played, why left-handedness persisted, and whether similar patterns might exist in other animals, such as parrots or kangaroos.

Background

The preference for one hand is related to lateralisation - the separation of functions between the right and left sides of the body and brain. In humans, this is particularly noticeable: many precise actions are more often performed with the right hand, and movement control is related to the way the brain's hemispheres work.

In the past, right-handedness was tried to be explained in different ways. Some hypotheses have emphasised tool making, others have focused on language and gestures, while still others have focused on social life, imitation or the benefits of group coordination. The new work doesn't dismiss these ideas entirely, but shows that without uprightness and brain enlargement, the picture would probably be incomplete.

It's also important to remember: left-handedness is a normal developmental variant. The study explains not "why left-handed people exist," but why there are so many right-handed people in human populations.

Source

Thomas A. Püschel, Rachel M. Hurwitz, Chris Venditti, "Bipedalism and brain expansion explain human handedness," PLOS Biology, 2026. The article was published on 27 April 2026.

In the study, the authors combined data on hand preference in 2,025 individuals of 41 primate species and used evolutionary modelling to test different explanations for human right-handedness. The most important factors were found to be traits related to uprightness and brain size.