But even granting these similarities, the differences, as illustrated in the comparison above, are striking, even if they are differences in degree rather than in kind. Note that the eye-openings of human beings are much larger than the iris, the colored part of the eye. A large portion of the sclera or white part of the eye is visible. We are the only mammal whose eye-openings are like this. Since human eye brows and eye-lashes are also dramatically visible (particularly on a model in a cosmetic advertisement), we can infer that these features are signal-enhancers. Our eyes enable us to communicate subtle states of mind or emotion at quite a distance, and it is important for us to be able to "read" and interpret each other's moods, attitudes, and impending actions in this way.

Note also that the lips of the model at right seem enlarged compared to the chimp, which has little lip development. Non-verbal sexual messages are very important in human communication, and smiles, along with intense and prolonged eye contact, constitute a universal language. We are, as our faces constantly reveal, very social creatures.