Study of the Day: Smaller Families May Lead to Smarter Children

A new longitudinal study in Personality and Social Psychology Bulletin shows that family size, not birth order, matters for intelligence.

Study of the Day

PROBLEM: Ever since Francis Galton noticed the preponderance of firstborns in the English scientific community (PDF), experts have weighed in on whether birth order affects intelligence. Theorists have argued that "laterborns" live in less cognitively stimulating environments filled with more kids and are left with fewer resources for the pursuit of knowledge. Since intelligence is fairly heritable, can this seeming birth-order effect be explained instead by the preference of smarter parents to simply have fewer children?

METHODOLOGY: London School of Economics and Political Science researcher Satoshi Kanazawa analyzed data from a British study of more than 17,000 people, who took multiple intelligence tests at ages seven, 11, and 16. He controlled for several variables, including fertility, social class, and parental educational background.

RESULTS: Children from larger families, regardless of their birth orders, tend to be less intelligent than kids in smaller households. Birth order is not associated with intelligence once the number of siblings is statistically controlled.

CONCLUSION: The apparent birth-order effect on intelligence may actually be due to family size. Since children largely inherit their intellects and less intelligent parents tend to raise more kids, the offspring of larger families tend to be at a cognitive disadvantage.

IMPLICATION: So why do smarter parents have fewer children? "More intelligent people are more likely to do unnatural things or things for which they are not evolutionarily designed to do," says Kanazawa, "and having fewer children is one such unnatural thing."

SOURCE: The full study, "Intelligence, Birth Order and Family Size," is published in the journal Personality and Social Psychology Bulletin.

Presented by

Hans Villarica writes for and produces The Atlantic's Health channel. His work has appeared in TIME, People Asia, and Fast Company.

How to Cook Spaghetti Squash (and Why)

Cooking for yourself is one of the surest ways to eat well. Bestselling author Mark Bittman teaches James Hamblin the recipe that everyone is Googling.

Join the Discussion

After you comment, click Post. If you’re not already logged in you will be asked to log in or register.

blog comments powered by Disqus

Video

How to Cook Spaghetti Squash (and Why)

Cooking for yourself is one of the surest ways to eat well.

Video

Before Tinder, a Tree

Looking for your soulmate? Write a letter to the "Bridegroom's Oak" in Germany.

Video

The Health Benefits of Going Outside

People spend too much time indoors. One solution: ecotherapy.

Video

Where High Tech Meets the 1950s

Why did Green Bank, West Virginia, ban wireless signals? For science.

Video

Yes, Quidditch Is Real

How J.K. Rowling's magical sport spread from Hogwarts to college campuses

Video

Would You Live in a Treehouse?

A treehouse can be an ideal office space, vacation rental, and way of reconnecting with your youth.

More in Health

Just In