NEW YORK, June 21 (UPI) -- Norwegian researchers have determined that first-born sons tend to have slightly higher IQ's than their younger brothers.
The study involved two sets of data, The New York Times reported. The first involved the military records of more than 241,00 men born between 1967 and 1976, while the second compared the scores on intelligence tests of 63,951 pairs of brothers.
The team found that older brothers had IQ's averaging just over 103 -- 3 percent higher than those for second-born sons and 4 percent higher than those born third. Sons who became the eldest in the family after the death of an older sibling also tended to have higher IQ's.
The study is to be published Friday in the U.S. journal Science.
Scientists have been arguing for years about the relationship between birth order and intelligence. Frank J. Sulloway -- a psychologist at the Institute of Personality and Social Research at the University of California in Berkeley -- who wrote an editorial to accompany the article, called the study "a dream come true."
