Big siblings have long suspected it, and now science backs them up: Oldest children have slightly higher IQs than younger kids. Family dynamics, not biological factors, account for the 3-point discrepancy, which holds up for children who become the oldest after the firstborn dies. That tiny gap may mean the difference between a "name" college and a state school.
Oldest kids don't just get more parental attention—they benefit from mentoring younger siblings. Researchers looked at records for Norwegian men and say the results, which appear today in the journal Science, likely extend to women. The sample, of more than 240,000 men, was large enough to be significant, the Times reports; one psychologist calls it "a dream come true." (Read more intelligence stories.)