Built for Combat

The most ticklish spots — neck, ribs, armpits, feet — are exactly the places you would protect first in a fight. That overlap is no accident. Many scientists think ticklishness evolved as defensive training, a way young mammals learn to guard their soft targets.

Even rats are ticklish. When researchers tickled them, the rats let out high ultrasonic chirps and the brain's reward circuits fired, the same ones active during play. Tickle laughter, it turns out, is far older than humans and runs deep in the mammal family.