Your family—the number of siblings you have and how old they are—has a big effect on whom you become, research suggests. For one thing, there's intellect: a large Norwegian study just confirmed that first-borns have slightly higher IQs than their younger siblings do. Because the study found that second-born children whose older sibling died at a young age are also slightly smarter and because “only” children do not show this IQ advantage, the intellectual disparity is more likely to be the result of differences in a child's environment after birth than of biological effects. Scientists speculate that eldest kids communicate with and coach their younger siblings, which requires them to consolidate knowledge at a young age and potentially gives them a slight intellectual edge. These findings build upon a body of research suggesting birth order and family size influence a number of traits and risk factors.
All in the Family
Birth order affects our personality and health
This article was originally published with the title "Ask the Brains" in SA Mind 18, 5, 9 (October 2007)