In 1922, Edward Treacher Collins, a British ophthalmologist, wrote that early primates needed sight that would "enable them to swing and spring with accuracy from bough to bough…to grasp food with their hands and convey it by them to their mouths". As our primate ancestors moved into the trees to escape their predators, the needs to navigate the tree branches and to grab rapidly fleeing prey with their hands, he argued, meant that evolution favoured a visual system with good depth perception.