A study by Norwegian scientists appearing in today's online edition of the journal Science concludes that a child raised as the eldest has a higher intelligence quotient, on average, than younger siblings. The difference is just a couple IQ points, but it adds an interesting twist to some famous sibling rivalries.

Slightly better brains appear to be a result of the way the senior child is raised and adapts to the family, not to any special genetic traits that go with coming first, the researchers say. The difference may help explain why it seems like Casey Affleck is riding on big brother Ben's coattails, and not the other way around.