Nature vs Nurture becomes especially interesting when the subjects are too young for life experience to play a large role. Babies aged 4 to 8 months have had almost no cultural training, yet the boys gaze at the truck more often and the girls gaze at the doll more often in a controlled toy-preference test. Because the toy positions are swapped each round to prevent bias, the pattern suggests that some preferences may come from birth rather than from life experience.

Studying behavior by watching what happens — without changing anything — is the core of observational research. In a toy-preference study at a daycare center, you set up a truck and a doll behind a curtain and reveal both toys to each baby one at a time. You watch each baby's eye movements for 10 seconds, then repeat the test three times per baby, swapping the toy positions each round. No physical intervention takes place. That careful watching protocol alone — not any manipulation of the babies or the toys — produces the data about which toy each baby prefers.