*1 The Allen Curve echoes another famous social metric, the Dunbar Number, which reflects the cognitive limit to the number of people with whom we can have a stable social relationship (around 150). They would seem to underline the same truth: Our social brains are built to focus and respond to a relatively small number of people located within a finite distance of us. One hundred and fifty feet also happens to be the rough distance at which we can no longer recognize a face with the naked eye.
