Compared to other primates, human muscles are rather weak. In hand to hand combat with a chimp, humans don’t stand a chance. It seems that because we are so good at using tools, we could avoid paying for expensive muscles. Similarly, compared to other animals, language lets humans talk more precisely, and talk about things not in our immediate view. So you might expect we’d get worse at non-language communication. You’d be wrong:
Humans are known to have the largest and most visible sclera – the “whites” of the eyes – of any species. This fact intrigues scientists, because it would seem actually to be a considerable hindrance: imagine, for example, the classic war movie scene where the soldier dresses in camouflage and smears his face with green and brown pigment – but can do nothing about this conspicuously white sclera, beaming bright against the jungle. There must be some reasons humans developed it, despite its obvious costs. In fact, the advantage of visible sclera – so goes the “cooperative eye hypothesis” – is precisely that it enables humans to see clearly, and from a distance, which direction other humans are looking. … Chimpanzees, gorillas, and bonobos – our nearest cousins – follow the direction of each other’s heads, whereas human infants follow the direction of each other’s eyes. (The Most Human Human, p. 39).
Note that most of what we learn via looking at each other’s eyes is hard to verifiably say via language. You might feel he is laughing at you with his eyes, but it will be hard to make that laugh the basis of a group response – others probably didn’t see his eyes at the right moment, or might interpret what they saw differently.
Language was a big innovation, but my homo hypocrites hypothesis is that we humans are now actually post-language in important ways. Language let us express and enforce social norms, but we’ve since developed powerful capacities to coordinate outside the scope of language, to evade those norms. The whites of our eyes seem a key part of that norm-evading capacity.