Proud parents are often first to make the positive visual ID, "What a sweet baby! She looks exactly like her father!" or "I beg to differ! She looks exactly like her mother!"
We smile, and because we're polite, we say we also see the resemblance, but how much do babies actually look like their parents? Could an impartial stranger match a roomful of babies with their moms and dads?
Psychologists at the University of California at San Diego recently set out to test this. They found that a one-year-old is more likely to resemble its father than its mother, but this resemblance fades as the child grows.
The test was conducted somewhat like a police line-up. Volunteers looked at mug shots of children ages one, ten, and twenty. They compared each child with photos of three possible mothers and three possible fathers. When trying to match one-year-olds with their mothers, the volunteers correctly identified only one in three, the same odds as random guessing. However, they got about half the fathers, suggesting that one-year-olds generally look more like dad than mom. By the time the child is ten or twenty, the success rate dropped back to one in three, even for dads.
Why should a one-year-old look significantly more like dad? Perhaps this evolved long ago to motivate fathers to take care of their offspring. After birth, mothers aren't likely to wonder whether a child is theirs, but a father might doubt his paternity. This early resemblance may have once given the infant a survival advantage by convincing dad to stick around.