Firstborn kids often grow up to earn more than their siblings. Germs and illness are big reasons why PlayBeing the firstborn in a family has a lot of advantages. Oldest siblings tend to have higher educational achievement and lifetime earnings than their younger siblings. A new study shows that germs play a big role in how younger siblings fare. “Germs in the Family: The Short- and Long-Term Consequences of Intrahousehold Disease Spread” was published in the American Economic Review.