The 2-Million-Year-Old Reason Why You Are Probably Right Handed : Milky Way News

EARTH, Laniakea Supercluster—Stand up. Now reach for something. Odds are nine in ten you just used your right hand.

Roughly 90 percent of people across every culture on Earth favor their right hand—a level of one-sidedness no other primate comes close to. While chimps and gorillas show only faint hand preferences, we are the lopsided outliers. And for decades, nobody could say exactly why.

But according to a new study conducted by researchers from the University of Oxford, you can thank your ancestors for getting off all fours and growing a bigger brain for that. The findings, published in PLOS Biology in 2026, explained how the researchers crunched data from 2,025 monkeys and apes spanning 41 primate species, to answer the longstanding mystery.

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Using Bayesian modeling that accounted for how those species are evolutionarily related, the team stress-tested the usual suspects behind handedness: tool use, diet, habitat, body size, social structure, brain size, and movement.

At first, humans looked like a total anomaly, until researchers folded in two specific traits—brain size and the arm-to-leg length ratio that signals bipedal walking—humans stopped looking so freakish. The combination, they argue, may be the engine behind our heavy right-hand bias.

"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,” said Dr. Thomas A. Püschel in the University of Oxford's announcement with ScienceDaily.

“By looking across many primate species, we can begin to understand which aspects of handedness are ancient and shared, and which are uniquely human."

The model even let the team rewind the clock. Early hominins like Ardipithecus and Australopithecus probably had only mild right-hand leanings, similar to today's great apes. The bias appears to crank up sharply with the genus Homo, for example, Homo ergaster, Homo erectus, and Neanderthals likely got progressively more right-handed until we hit modern levels.

The fun outlier: Homo floresiensis, the tiny "hobbit" species. Researchers predict it had a notably weaker right-hand bias, which tracks with its small brain and body still kitted out for both climbing and walking, according to the University of Oxford.

The picture they paint is a two-stage process. First, walking upright freed the hands from getting us around, opening the door to specialized, asymmetric hand use. Second, ballooning brains supercharged the right-hand preference into the near-universal trait it is today.

Big questions remain.

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The University of Oxford notes scientists still don't fully understand why left-handedness has stuck around, or how culture reinforced the rightward tilt. They're also eyeing limb preferences in parrots and kangaroos for deeper clues.

So next time you brick a wide-open left-handed layup while playing pick-up, don’t flop and claim you were fouled. Instead, just blame your ancestors for getting off all fours and evolving such a big, lopsided brain.