Our ability to perceive all three dimensions, due in part to having two eyes on the front of our heads with overlapping visual fields, allows us to enjoy 3D summer blockbusters, but may have originally evolved for a simpler purpose: avoiding falling to our deaths.
If you're going to be able to effectively navigate the world, one thing that seems almost indispensable is the ability to perceive depth. It's an ability that most of us take for granted, since it runs in the background of our minds, outside of conscious awareness. Philosophers going back hundreds of years, like Descartes, wondered whether the ability to see in depth was a feature inherent to the mind or if it required learning in the earliest days and weeks of life.
In the last few decades, researchers have become able to address that question by using the tools of modern cognitive and comparative psychology.
Read about it in my latest piece at Nautilus Magazine: Depth Perception & Death Prevention: Babies’ Visual Instinct
Photo of infant on visual cliff from Gibson & Walk's 1960 article in Scientific American magazine.