What Your Birth Order Says About Your Health, Wealth, And IQ

If you grew up with siblings, you might have noticed your family either adhering to or defying birth order tropes – think “the responsible eldest daughter” or “the invisible middle child”.

As it turns out, scientists reckon birth order might actually affect your health, wealth, and even IQ.

Here’s what the research says:

Some data suggest that first-borns are 13% less likely to smoke than fifth-borns, while first-borns are “more likely to be overweight, to be obese, and to have high blood pressure and high triglycerides”.

Meanwhile, first-borns seem likelier to have ADHD and/or autism than those born later. They’re also at a higher risk of food allergies and hayfever.

And second-borns may be more prone to substance abuse, migraines, shingles, and gut issues.

Firstborns seem to perform higher on IQ tests than their younger siblings, even in tests conducted as early as one year old.

Some think that might explain why oldest children could end up more successful and rich, too. A 2014 study found that eldest daughters are the most likely to succeed out of any sibling type; a 2012 study suggests first borns are more likely to hold leadership roles.

Last-borns seemed to be the most social and resilient, followed by first-borns, middle-borns, and only children in a study that quizzed parents on their kids’ qualities.

In the same research, middle-borns appeared the least happy.

Some think it might have to do with how parents treat each new child – perhaps the eldest gets the most emotional investment. “Firstborn kids get the undivided attention of their parents, whereas kids born later are often competing for parental time and resources,” NPR suggested.

Then, there are the peer groups of each sibling to consider. An only or eldest child looks up to their parents, while a younger sibling might “have role models who are slightly irrational two-year-olds, you know, their older siblings”.

With that said, birth order traits are far from universal, and not everyone agrees on how much of a difference it makes to things like intelligence and personality.