Humans have historically lived in groups of about 100, yet our facial recognition skills easily adapt to a modern world where we see endless faces each day, whether in person or on TV. A new study in Proceedings of the Royal Society B, the first to give an evidence-based estimate of how many faces the average human knows, puts the number at an impressive 5,000, though some participants recognized as many as 10,000, reports the Telegraph. "Given the social lives of our ancestors, the ability to recognize thousands of individuals might seem like overkill," but "we haven't yet found a limit on how many faces the brain can handle," University of York psychologist Rob Jenkins explains in a release.
Twenty-five volunteers were given an hour to recall as many faces as possible—belonging to friends, acquaintances, famous people—and came up with 550 on average, reports Nature. They were then shown 3,441 faces of famous people and recognized 800 on average. Estimating "facial vocabulary" based on the ratio of famous faces recalled versus recognized, and how a person's recall rate slowed, researchers were "surprised by how high the top end was," co-author Mike Burton tells the Guardian. However, we have faults with the unfamiliar. For example, "people are surprisingly bad at checking a real face against a photo ID," Burton adds. (While it still has much to learn from our own abilities, facial recognition technology does better in this regard.)