Why eldest siblings are smarter

Imagine discovering that the real reason firstborns tend to be brighter has nothing to do with discipline or higher parental expectations, but rather with a matter of… germs. We are used to thinking that firstborn children are successful because they are more responsible, or because their parents pour all their parenting energy into them in the early years. However, according to recent research published in The Economist, the reason is something else: infections. The data show that, on average, firstborns perform better in school and earn more in adulthood than their younger siblings. So far, nothing new. But the surprise comes when you look for the cause. Stereotypes lead us to imagine the older sibling as the serious and reliable one, and the younger siblings as the family's rebels. However, very large studies have found no strong link between birth order and personality. This is where the science of microbes comes into play. According to this new research, siblings born after the first child are exposed to more germs from a very young age, simply because they live with another child who brings home viruses and bacteria from daycare or school. And this increased exposure to infections in the early years of life appears to have effects on neurological development. The theory is that repeated illnesses in the early years—even simple flu infections—may slightly slow down certain cognitive processes. This difference is minimal, almost imperceptible in individual cases, but when multiplied by millions of families, it creates a statistical trend: on average, firstborns have a slight advantage. One of the most striking stories involves a Dutch family where the second child, not even two years old, had already had five severe colds brought home by his older sister. The mother reports that the baby was often tired and less responsive in the first few months. This is not conclusive evidence, but it is a concrete example of how the presence of an older sibling literally changes the biological environment in which a child grows up. The most thought-provoking fact is that the “brighter brain” effect seen in firstborns is not observed in only children: it is precisely the dynamic of cross-infection between siblings that is needed. However, there is an interesting counterargument: while it is true that firstborns are more protected in their first few months of life, it is also true that younger siblings, as they grow up, develop a more robust immune system and a greater ability to adapt socially – advantages that do not end with school tests, but can matter a great deal in real life. Ultimately, being the firstborn or the second-born makes less of a difference than we think: the environment, germs, and chance play a greater role than family myths. The takeaway here is this: the difference between siblings is not just a matter of personality or upbringing—sometimes it's a matter of viruses. If you found the idea that a simple flu can change a person's destiny compelling, you can indicate this on Lara Notes using I'm In – it's your way of saying that this insight is now part of how you view the world. And if you happen to tell this story to someone tomorrow, you can use Shared Offline: tag the person you talked to about it and make that conversation memorable. This idea comes from The Economist, and today you saved a couple of minutes compared to reading the original article.