Germs Give Eldest Siblings an Edge?

New research suggests that germs, not personality, explain why first-born children often achieve greater success in education and income. Younger siblings are notably more susceptible to severe respiratory illnesses during their first year, with Danish data indicating a two to three times higher likelihood of hospitalization compared to their older siblings. These early health challenges can impede brain development, leading to a lasting impact on adult wages.

The study estimates that illness accounts for about half of the wage gap between first- and second-borns. The remaining difference is attributed to parental behavior. First-born children receive an estimated 20-30 minutes more quality time per day throughout childhood, potentially providing crucial brain-boosting stimulation in their formative years.