About one person in ten is left-handed, and that number has not moved in 130,000 years.
We know because of scratches on Neanderthal teeth. They clenched hide between their front teeth, pulled with one hand and cut with a stone blade in the other, and every time the blade nicked the enamel it left a scratch at an angle. The angle tells you which hand held the knife. Across 35 Neanderthals from Spain to Croatia: 32 right-handed, 3 left-handed. The same split you would get from a room of people today.
That stability is the real puzzle. If left-handedness were worse, selection would have removed it. If it were better, it would have spread. Something is holding it exactly there.
It is not simple genetics. The largest study ever run, 1.7 million people, found 48 genetic variants that together explain about 3.45 percent of it. Identical twins with identical genomes routinely disagree about which hand they write with.
In 1991 a paper reported that left-handers died nine years earlier than right-handers, 66 against 75, from 987 death records. It made headlines worldwide, and it was an artefact. Left-handed children had been forcibly retrained for most of the twentieth century, so older people born left-handed reported as right-handed, which made left-handers appear to vanish from the older age groups. Corrected for that, the real difference is 0.43 years. A century of punishing left-handed children produced the statistic that appeared to justify the punishment.
So what does hold it at ten percent? The leading answer, contested rather than settled, is that the advantage is unfamiliarity. The best test came in 2017, when six elite sports were sorted by how much time a player gets to react. In men’s squash, where rallies are long and you can adapt inside a point, 8.7 percent of the elite are left-handed, which is simply the population baseline. In baseball pitching, cricket and table tennis, where the ball arrives in a fraction of a second, it is 30.4 percent. Same athletes, same population, triple the share, and the only variable is time.
Which means the advantage is made entirely of scarcity. If left-handers became common, opponents would grow familiar with them and the advantage would erode. Ten percent is not an accident. It is an equilibrium.
CHAPTERS
0:00 Look at your hands
1:10 How we read handedness off a skull
1:53 Thirty-two right, three left
2:20 It is barely inherited
3:31 The study that terrified a generation
4:49 They had been erased
5:46 The gap does not shrink, it disappears
6:20 So what holds it at ten percent?
6:39 Eight societies, and homicide
7:33 The test is time, not practice
8:37 Triple the share
8:57 Made entirely of scarcity
9:47 We treated them as broken
SOURCES
Frayer et al., handedness from oblique striations on Neanderthal teeth. 35 individuals, 32 right to 3 left
https://news.ku.edu/2016/07/21/study-finds-earliest-evidence-fossil-record-right-handedness
“Hand to Mouth in a Neandertal,” PLOS ONE (2012)
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0043949
Cuellar-Partida et al., “GWAS identifies 48 common genetic variants associated with handedness,” Nature Human Behaviour (2021). 1.7 million people, 3.45% SNP heritability
https://www.nature.com/articles/s41562-020-00956-y
Coren and Halpern, “Left-handedness: a marker for decreased survival fitness,” Psychological Bulletin (1991). The nine-year claim. Rebuttal:
https://pubmed.ncbi.nlm.nih.gov/8416031/
“Modeling to explore and challenge inherent assumptions when cultural norms have changed,” Archives of Public Health (2023). The corrected 0.43 years
https://link.springer.com/article/10.1186/s13690-023-01156-6
On the forced retraining of left-handed children
https://www.press.jhu.edu/newsroom/stuttering-and-retraining-left-handed-children-mid-century-us
Faurie and Raymond, “Handedness, homicide and negative frequency-dependent selection,” Proc R Soc B (2005)
https://www.researchgate.net/publication/7864491_Handedness_homicide_and_negative_frequency-dependent_selection
The counter-evidence, which the video states out loud:
https://www.sciencedirect.com/science/article/abs/pii/S109051381100064X
Loffing, “Left-handedness and time pressure in elite interactive ball games,” Biology Letters (2017)
https://royalsocietypublishing.org/rsbl/article/13/11/20170446/87957/
Companion video: Picture An Apple. Some People See Nothing. This Is Aphantasia.
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