Born to Be Smarter

I always knew my older brother was smarter than I. Now, a study confirms this by associating birth order with intelligence. But, is it being the oldest or being the firstborn that is associated with higher IQ? The investigators distinguished between biologic birth order and social birth order by examining intellectual performance in men whose older siblings had died.

The subjects were 241,310 male Norwegian conscripts born from 1967 through 1976. The intellectual test administered to the conscripts is highly correlated to IQ. The researchers examined only sibships with intelligence test results and with at least one male born first, second, or third.

Analyses were adjusted for possible confounders, e.g., parents’ education. Firstborn men had …