Lefties, Raise Your Hands

August 12, 2026

AI Summary

5 min read

Why 90% of People Are Right-Handed—and What Lefties Reveal About the Brain

About 90% of humans are right-handed, a figure that holds across every culture on Earth. But among our closest primate relatives, the split between right- and left-handedness is roughly even. For decades, scientists couldn't explain why humans are the outlier. A new statistical analysis from the University of Oxford and University of Reading may have cracked it—and the answer has less to do with hands than with legs and brains.

The Evolutionary Shift That Made Us Right-Handed

The researchers analyzed data from over 2,000 monkeys and apes across 41 species, using Bayesian modeling to test which traits best predicted handedness. They looked at diet, body size, social structure, habitat, movement patterns, and tool use. In every case, humans stood apart. But when they plugged in two specific evolutionary developments—bipedalism and brain size—humans no longer looked like anomalies.

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What you'll learn

1 (01:40) **Why 90% of Humans Are Right-Handed** - The host introduces the episode's central puzzle: the extreme right-handedness of humans compared to other primates.
2 (08:26) **Interview: Dr. David Carey on Left-Handed Brains** - Clinical neuropsychologist Dr. David Carey joins to discuss brain asymmetry in left-handers.
3 (10:45) **The Corpus Callosum and Language Dominance** - Dr. Carey debunks the old theory that left-handers have a larger corpus callosum to connect a language-dominant left hemisphere to a left hand.
4 (12:09) **Clinical Implications of Handedness** - Dr. Carey discusses how handedness affects neurological diagnosis and recovery after stroke.
5 (14:54) **Complementary Hemispheric Specialization** - Dr. Carey explains how the brain's two hemispheres take on complementary roles, using face and language processing as an example.
6 (16:22) **Footedness, Sighting Dominance, and Other Asymmetries** - The conversation expands from handedness to other physical biases like footedness and eye dominance.
7 (18:31) **Handedness in Sports: The Fencing Advantage** - Dr. Carey discusses the competitive advantage of left-handedness in specific sports like fencing.

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Show Notes

Most people are right-handed. So this episode, we are celebrating International Left-Handers Day to honor the 10% of the population that are left-handed. To discuss the unique elements of the left-hand brain, host Dr. Samantha Yammine speaks with clinical neuropsychologist Dr. David Carey. She also dives into the question of why so many people are right-handed and later, she explores a study that shows how to figure out which paw preference your dog has.

Link to Show Notes HERE

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