Researchers at Britain's University of York say facial recognition abilities that allow a person to process 5,000 faces daily is an evolutionary wonder.
"In everyday life we're used to identifying friends, colleagues, celebrities and many others by their faces," says Rob Jenkins of York's Department of Psychology. "But no one has established how many faces people actually know."
So the Jenkins team asked people to write down as many faces they could remember from their personal lives. Then they did the same with people they recognized but did not know personally. They were also shown thousands of images of famous people -- two of each to ensure consistency -- and asked which ones they recognized.
The team found each person could recall from about 1,000 to 10,000 people. "So people know 5,000 faces on average," Jenkins says.
The team thinks its study can help with facial recognition software, though Jenkins admits: "Familiar faces are identified very reliably, but we don't know how."
For thousands of years humans would have met only dozens of people throughout their lives, and Jenkins says it's unclear how we developed an ability to distinguish between thousands of faces in a crowd.