“When our earliest human ancestors left the trees and moved to the open grasslands of the savanna, they adopted an upright stance. Possessing already this powerful visual system, they could see far into the distance (giraffes and elephants might stand taller, but their eyes are on the sides, giving them instead panoramic vision). This allowed them to spot dangerous predators far away on the horizon and detect their movements even in twilight. Given a few seconds or minutes, they could plot a safe retreat. At the same time, if they focused on what was nearest at hand, they could identify all kinds of important details in their environment—footprints and signs of passing predators, or the colors and shapes of rocks that they could pick up and perhaps use as tools.”