Conversation: Oh, Brother!

What makes one brother a star and another a flop?

How to explain Bill and Roger Clinton? Dalton Conley, a sociology professor at New York University and the author of The Pecking Order: Which Siblings Succeed and Why (Pantheon) studied Census data and 175 siblings for answers. Conley points not to birth order but to family size and economic influences. "Inequality," he says, "begins at home." TIME spoke with Conley:

What is the family pecking order?

The pecking order is the hierarchy within the family based on the class or socioeconomic status of the adult kids. I define class by four measures: their educational level, the prestige of their occupation, how much money they earn and how much wealth they've accumulated. There's this enormous amount of socioeconomic difference between siblings from the same families.

Do parents love their children equally?

As a parent, I would say 99% of parents love their kids equally. But love is just one thing you're giving your kids. The fact that you do love them equally may be blinding you to the fact that they are receiving different resources and they have different needs.

Do you believe that there's always a favored child?

As a parent, I'll say no; as a researcher, I'd say yes.

What is the impact on siblings of being in a very large family?

Each family has a pie of resources. By resources I mean parental time, energy and, of course, money. Some families have extra-large, supersize pies, and some have small pies. But no matter what the size of the pie, if you're going to slice it into more and more slices, each kid is going to get a smaller slice.

What did you learn about middle children?

In families with three or more kids, the middle children ended up getting short shrift from the parents, unbeknownst to the parents. The problem was that they were less likely to get educational investment, and they were therefore more at risk to fail educationally.

What's your view of birth-order theories?

A lot of people talk about birth order--firstborns are driven and born leaders, last borns are gregarious and outgoing, middle borns are mediators. As far as I understand it, the evidence for those personality-based theories is pretty weak. But even if it were strong, the links are really weak between personality and the kind of outcomes I'm interested in: who's succeeding in school, who's making more money.

You write about "outsider status." What do you mean by that?