The fear of heights is developed in infants while they are moving around in their environments, a new study explains.
Learning to avoid cliffs, ledges, and other precipitous hazards is essential to survival and yet human infants don't show an early wariness of heights.
As soon as human babies begin to crawl and scoot, they enter a phase during which they'll go over the edge of a bed, a changing table, or even the top of a staircase.
In fact, research shows that when infants are placed near a virtual drop-off - a glass-covered table that reveals the floor beneath - they seem to be enthralled by the drop-off, not fearful of it.
It's not until later in infancy, at around 9 months, that infants show fear and avoidance of such drop-offs.
And research suggests that infants' experiences with falls don't account for the shift, nor does the development of depth perception.
The study is published in Psychological Science, a journal of the Association for Psychological Science.