Your two hands are radically different from the other — not only in the distinct microbial populations they carry but in their cultural baggage as well. The symbolism of the right hand as the doer and the left as the dreamer compelled the pioneering Harvard psychologist Jerome Bruner to write an entire book about it — one of the most insightful books ever written, no less. Even as modern science disperses centuries-old superstition, the evolutionary mystery of handedness continues to fascinate.

The enduring enigma of why a tenth of all humans are left-handed is what the fine folks at TED-Ed distill in this animated primer:

Handedness seems to be determined by a roll of the dice, but the odds are set by your genes.

Dive deeper into the scientific detective story of left-handedness here, then revisit other stimulating TED-Ed animations exploring how melancholy enhances creativity, what makes a hero, how you know you exist, and why playing music benefits your brain more than any other activity.