ScienceShot: Strong Jaws, Tiny Index Fingers

Kirk Douglas may have nabbed man's-man roles in Spartacus and other films by virtue of his jutting jaw. But casting directors seem to have missed one of the actor's manlier traits: a stubby index finger. Scientists have known that men boasting traditionally more masculine mandibles—think Douglas's iconic cleft chin—also tend to have short pointer fingers relative to their ring fingers. But no one knew if the trend held true for kids not yet through puberty. To find out, researchers photographed 17 boys between 4 and 11 years old. And, sure enough, those with more petite trigger fingers also bore bigger, rounder chins (at right). They also had smaller foreheads and thicker eyebrows, the group reports online in the Proceedings of the Royal Society B. High levels of in utero testosterone may help to shape both the digit mismatch and the lads' faces, pointing the importance of the hormone even early in life. Call it the Spartacus, Jr. effect.

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