What's Left?

Left-handedness is rare, biologically rooted, and tied to how the brain manages efficiency—while “what’s left” also becomes a pivot to the dwindling resource humans may be overlooking: helium. Roughly 90% of people are right-handed across cultures and languages, and that preference appears before birth. When fetuses are observed sucking their thumbs, the behavior skews heavily toward the right thumb. The pattern shows up in animals too: horses tend to take longer strides with their right legs, a detail often linked to why racetracks run counterclockwise.

Because left-handedness is uncommon, many cultures historically treated it as suspect. Language itself reflects the bias. “Dexter” and “right” are etymologically linked, while “ambidextrous” literally points to “two right hands,” not equal skill with both. “Ambisinister” similarly uses Latin roots—“sinister” meaning left—to describe people who can’t reliably use either hand.

The underlying reason for having a dominant hand comes down to the brain’s wiring and energy costs. The brain tends to assign tasks to specific regions and avoids constant cross-communication between hemispheres because that would require heavy reliance on the corpus callosum, which takes time and energy. Hand dominance also tracks with brain lateralization: the left hemisphere controls the right side of the body, and the right hemisphere controls the left side. In about 95% of right-handed people, the left hemisphere handles precise language and thinking. For left-handed people, the pattern shifts—there’s roughly a 40% chance that the right hemisphere or both hemispheres take on those precise functions.

That doesn’t mean left-handers have a single, uniform brain type. Still, population-level correlations have been reported: ambidextrous people sometimes score lower on IQ tests, and a higher proportion of people with schizophrenia are left-handed or ambidextrous than in the general population. The story isn’t purely negative, though. More inter-hemispheric sharing can mean more novel connections and potentially more creative thinking. Famous examples are cited: Albert Einstein was left-handed, and five of the last seven US presidents were left-handed.

The advantages show up in everyday skills. On a QWERTY keyboard, the left side contains many letters that allow long English words to be typed with the left hand alone, while the right side has far fewer options—one of the longest commonly typed words on the right is “lollipop.”

Finally, “left” expands beyond bodies and brains to the question of what resources remain. Helium “leaves” Earth in a literal sense: it rises through the atmosphere and is eventually stripped away by solar wind. Helium is also hard to replenish because it forms on Earth mainly through radioactive decay, with alpha particles acting as helium nuclei and natural gas containing helium. With current consumption and helium’s low natural replenishment rate, the transcript warns that within 30 to 40 years there may be little helium left.