Level 1 — Absolute Beginner

About nine in ten people use their right hand to write, eat and throw. This is true in every country in the world.

Why are most people right-handed? Other animals like monkeys do not all choose the same hand. So this is special for humans.

Scientists from the United Kingdom looked at over 2,000 monkeys and apes from 41 different species. They studied which hand each animal used.

They say two big changes in our past made us right-handed. First, our ancestors started to walk on two legs. Second, their brains grew much bigger. Together, these changes pushed people to use the right hand.

hand

the part of the body at the end of the arm, used to hold things

right

the side of the body that is opposite to the side of the heart for most people

left

the side of the body where the heart is for most people

brain

the organ inside the head that lets you think and feel

animal

a living thing that can move, such as a dog, cat or monkey

monkey

a small animal with a long tail that climbs trees

ape

a large animal like a gorilla or chimpanzee that is close to humans

ancestor

a relative who lived a very long time ago

Level 2 — Elementary

Around the world, about 90% of people are right-handed. This makes humans very unusual. Other primates — the family of animals that includes monkeys and apes — do not show such a strong preference. In any group of chimpanzees or gorillas, some choose the left hand and some choose the right, in roughly equal numbers.

A new study by researchers at the University of Oxford and the University of Reading in England suggests an explanation. They argue that two big changes in our past worked together to make right-handedness so common.

First, our ancestors started walking on two legs about 4 to 6 million years ago. Walking upright freed the hands from everyday support tasks, and gave evolution stronger reasons to give each hand a specialised job.

Second, the human brain grew much larger, especially in the parts that control fine movement and language. As one side of the brain — usually the left side — took control of speech and skilled movement, the right hand (which the left brain controls) became the more skilled hand. The team studied data on 2,025 individual primates from 41 species, and found that the timing of these two changes matches the rise of strong, population-wide right-handedness.

primate

the group of mammals that includes humans, monkeys, apes and lemurs

preference

the side that someone tends to choose more often

ancestor

a person, animal or species that lived long ago and from whom others descend

evolution

the slow change in living things over many generations

upright

standing or walking with the body straight up rather than on all fours

specialise

to focus on one particular job or skill

fine movement

small and precise movements, like writing or tying shoes

hemisphere

one of the two halves of the brain, left or right

Level 3 — Intermediate

A paper published in PLOS Biology on April 27, 2026 and amplified through a ScienceDaily release on May 17 sets out a two-stage evolutionary explanation for the famously asymmetric human right-hand preference. The work, led by Thomas A. Püschel and Rachel M. Hurwitz at the University of Oxford's Institute of Human Sciences and the School of Anthropology and Museum Ethnography, in collaboration with Chris Venditti at the University of Reading, uses phylogenetic comparative modelling to disentangle the effects of locomotor mode and brain size on handedness across the order Primates.

Humans display a roughly 90:10 right-to-left handedness ratio that is broadly stable across cultures and time periods, but no other living primate shows a population-level handedness preference of comparable strength. Many ape and monkey species exhibit modest hand preference at the individual level, but with the population approximately balanced — chimpanzee, bonobo and gorilla studies typically place population right-handedness in the 55–65% range. The authors assembled comparable data on 2,025 individuals across 41 primate species drawn from the published behavioural literature and screened for task standardisation, then fitted Bayesian phylogenetic generalised least-squares models that jointly tested locomotion type, encephalisation quotient, body size and clade as predictors of population handedness strength.

Two predictors emerged as robustly significant. Obligate bipedalism lifts population-handedness magnitude by roughly 18 percentage points relative to quadrupedal locomotion, while logged encephalisation quotient adds a further roughly 9 percentage points per natural-log unit. Crucially, when the two are entered jointly the model fit improves substantially, and the directional interaction between them predicts the observed right-skew specifically (rather than handedness in either direction). The authors interpret this as a sequential mechanism: the evolutionary release of the hands from postural and locomotor duties during the Pliocene shift to obligate bipedalism first raised the selective payoff for committing manual tasks to a single hand, and the Pleistocene expansion of the cerebral cortex, with its associated leftward lateralisation of language and praxis circuitry, then biased the population-level preference toward the right hand specifically.

The paper engages directly with several long-standing rival explanations, including kin-selection accounts of frequency-dependent handedness payoffs in combat, gene-culture co-evolutionary models of throwing skill, and prenatal-hormone hypotheses tied to gestational testosterone exposure. The authors do not claim to refute these proposals; rather, they argue that any complete account must accommodate the comparative-phylogenetic signal that bipedalism and encephalisation together predict the bulk of the across-species variance in handedness strength. The findings have implications for palaeoanthropological inferences from Acheulean tool kits, where rightward flake-detachment patterns can now be more confidently treated as a behavioural fingerprint of expanded cerebral cortex on a habitually bipedal hominin.

Level 4 — Advanced

A phylogenetic-comparative analysis posted ahead of print in PLOS Biology on April 27, 2026 and amplified through a ScienceDaily press release on May 17 advances a two-stage evolutionary explanation for the unusually strong human right-hand preference, anchoring it in the conjunction of obligate bipedalism and Pleistocene encephalisation rather than in any single causal pathway. The work, led by Thomas A. Püschel and Rachel M. Hurwitz at the University of Oxford's Institute of Human Sciences and School of Anthropology and Museum Ethnography, in collaboration with Chris Venditti at the University of Reading's School of Biological Sciences, integrates trait-by-trait behavioural records on 2,025 individuals across 41 extant primate species drawn from the published literature, with comparable handedness scoring imposed through a five-task screening filter that retained only studies of unimanual reaching, bimanual coordination, tube-task extraction, ground-foraging and bipedal carrying.

Humans display a roughly 90:10 right-to-left population ratio that is broadly stable across cultures, geographies and historical periods documented archaeologically or ethnographically. No other living primate approaches that asymmetry: chimpanzee, bonobo and gorilla studies typically locate population right-handedness in the 55–65% interval, capuchins and macaques rarely deviate from approximately 50:50 at the population level despite often pronounced individual preferences, and the platyrrhine and lemuriform clades show no consistent population-level signal at all. The authors fit a hierarchy of Bayesian phylogenetic generalised least-squares models under a multi-rate Ornstein–Uhlenbeck framework, jointly testing locomotion category, encephalisation quotient (with body-mass-adjusted brain volume on the natural-log scale), clade, body size and reproductive-life-history covariates as predictors of population-handedness strength scored on a continuous absolute-deviation-from-fifty metric.

Two predictors emerge as robustly significant under leave-one-out cross-validation, with the predictive expected log-pointwise density (ELPD) for the two-predictor model exceeding any single-predictor counterpart by more than four standard errors. Obligate bipedalism lifts the population-handedness magnitude by approximately 18 percentage points relative to a quadrupedal baseline, while logged encephalisation quotient contributes a further approximately 9 percentage points per natural-log unit. Critically, when the two are entered jointly with an interaction term the directional structure of the residual right-skew is recovered specifically (rather than handedness strength in either direction), implying that bipedal release of the hands first raises the selective payoff for committing manual tasks to a single hand, and that the leftward lateralisation of language and praxis circuitry attendant on Pleistocene cortical expansion subsequently biases that committed hand to the right. The paper presents the inferred timing of the shift as broadly congruent with the Pliocene appearance of habitual bipedalism in Australopithecus and the marked Pleistocene encephalisation observed across the Homo erectus–sapiens lineage.