Science Looks At The Sibling Effect Are you a first-born? A middle child? A twin? An only child? In his new book The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us, author Jeffrey Kluger describes current scientific research into the effects of siblings on human behavior, from birth order studies to sibling rivalries and fighting.

Science Looks At The Sibling Effect

Science Looks At The Sibling Effect

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Are you a first-born? A middle child? A twin? An only child? In his new book The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us, author Jeffrey Kluger describes current scientific research into the effects of siblings on human behavior, from birth order studies to sibling rivalries and fighting.

IRA FLATOW, host: Next up, do you have a brother or a sister, maybe even more than one, and have you ever wondered how your life might have been different had you not had siblings or if you had been the oldest, the youngest or a middle child or if you had a lot of other siblings?

In recent years, scientists have been working to tease out what effect siblings have on people. Siblings always fight. You know, for example, is that sibling rivalry a good thing? What if it extends into adulthood? Is that a positive thing? How does that affect you?

Joining me now to talk about it is Jeffrey Kluger, he is senior editor and writer at Time magazine author of "The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us," just out from Riverhead. He's here in our New York studios. Welcome to SCIENCE FRIDAY.

JEFFREY KLUGER: Thanks for having.

FLATOW: So did you discover anything about yourself from doing this research? Do you have any brothers and sisters?

KLUGER: I have multiple brothers and sisters. I have three full brothers. I have a half-brother and a half-sister. There was a time when I had two step-sisters. And in addition to being scientifically and journalistically fascinated with the topic and having done a lot of work on it, I'm also intimately involved with it and have been profoundly shaped by those relationships.

FLATOW: Does it matter which order you are?

KLUGER: It does, and birth order is one of those rare things that the average person came upon even before scientists really began realizing it. The population had it right before the folks in the labs did. And it is essentially, very broadly, true that firstborns will be the most successful. They will be the ones who earn the most. They will be the ones who are most loyal to the family, most driven to achieve in traditional ways.

They will also be the tallest, even if it's only by a few centimeters, and they tend to have higher IQs by about three points over the second-born.

FLATOW: Well, that explains all my shortcomings.


FLATOW: You're listening to SCIENCE FRIDAY. I'm Ira Flatow. We're talking with Jeffrey Kluger. New book out: "The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us." 1-800-989-8255. For good or bad, siblings can teach us about new things. You know, you depend on your older brother or sister to teach you how to cook, how to throw a baseball, whatever.

Does this carry over into later life somehow? Does it affect us for how we deal with other people?

KLUGER: Absolutely, and one of the most profound effects siblings have on you is that area of conflict resolution skills, that area of relationship formation and maintenance. And, you know, what I - the analogy I like to use is that what goes on in the playroom is a little bit like kittens wrestling.

Kittens aren't really trying to hurt one another when they bite each other in the neck. They always hold back. But what they learn and what they learn when they're wrestling is what they'll use later when they do kill a mouse.

When kids are in playrooms, those skills they practice again and again and again are taken out with them to the playground and to the classroom and to life later on. And a lot of studies do show that conflict resolution skills that are evident when kids are two tend to be used when kids are five, and they're in preschool and kindergarten.

FLATOW: So if you resolved your conflict by batting your brother over the head with a toy, is that what you're going to do later in life?

KLUGER: Well, only to a point, because at some point you go to prison for that.


KLUGER: But yes, one study did show that, particularly among boys, since they tend to be more pugilistic than girls, particularly among boys, physical fighting at home does tend to translate to a greater likelihood of physical fighting at school then later on. Now, again, obviously in adulthood you're not going to be slugging people in bars without getting busted for it, but it does mean that your conflict resolution skills will be worse, and you'll tend to revert to verbal violence or verbal hostility.

FLATOW: If you went to your parents instead and sought their ability to resolve it, does that also carry over?

KLUGER: Well, yeah, the ability to seek wise intervention certainly carries over, and I tell my two school-age children that all the time. You know, come to me first. Let me see what you can - you know, let's see if we can resolve it, although there is - one of the canards that a lot of parenting texts will teach is that unless kids are killing each other in the playroom, you really should stay out and let them resolve those things.

And there is truth to the fact that parents can't possibly police every fight. They would do nothing else. But when kids - when parents do intervene, they help kids learn more sophisticated conflict resolution skills, like the ability to apply a resolution that they learn in Tuesday's fight to Friday's fight, if Friday is about the same thing.

If kids don't get parental intervention, it's sort of like "Groundhog Day," they keep having the same fight again and again.

FLATOW: As baby boomers are aging, are they finding solace in their siblings?

KLUGER: Absolutely, and one of the points I make, one of the most salient points I make, is that siblings are the longest relationships we'll ever have in our lives. Our parents leave us too soon, our spouses and our kids come along too late. As baby boomers age, a lot of us are getting into our 80s and our 90s and beyond, and by definition one spouse is going to outlive another.

So a lot of people are going to wind up in senior adulthood without a husband or wife, their kids have scattered to other cities, and the only people left at the dance will be the ones what brung them, which is their brothers and sisters.

FLATOW: And looking at it from the other direction, these - the baby boomers have aging parents that need to have special care now.

KLUGER: That's right.

FLATOW: I have seen cases where people - in both ways, where siblings who haven't spoken to each other in years are now forced to come back and share the care.

KLUGER: Right, that's right, and this is one area that I also stress, a couple of points. First of all, this raises favoritism issues among a lot of kids because, you know, if the older brother has always been mom's and dad's superstar, but it's the sister who happens to live in the city as the parents, and she suddenly winds up taking care of them, you know, there's a good reason for some resentment there if he's off making millions of dollars on Wall Street.

So it is a good time not to relitigate those fights of childhood but at least to try to see if you can resolve them.

Also, the idea that - one study showed that about 10, 15 percent of sibling relationships truly are so toxic that they're - that they're irreparable. But 85 percent are anywhere from fixable to terrific. And you know, the argument I make, particularly when it comes to taking care of aging parents, is if you can fix them, do. Your sibs are just such a resource.

FLATOW: I have seen cases where people have come back together, you know, have rediscovered a little bit of something in common, in taking care of mom and dad, or mom.

KLUGER: That's right, and hardship can often do that. That's one of the reasons that you find that when siblings - when parents divorce, siblings as a rule tend to get closer rather than further apart, because the two anchors in your life, mom and dad, are becoming completely unmooored. So the sibs tend to hold more tightly. That's what happened in my family.

FLATOW: Yeah. Is it easy or hard to do research about siblings?

KLUGER: It's both easy and hard, and that's not just the easy answer. The hard reason is that it's only about 15 years ago that scientists really began pouring themselves into this because the belief was always that siblings are fungible. They're household inventory. You stock your shelves with them, and the only limit to how many kids parents had is sperm, eggs and economics. As long as they can have them and support them, they should keep doing it.

They have none of the uniqueness of parents or your own kids. So the research didn't really begin until 15-or-so years ago in any vigorous way. But now that it's begun, it's easy to do it because so many people are piling into the field, and so many people like to talk about it.

We're all informed by our sibling experiences. We either had them or were raising them. Some people were only children who have no kids, but that's a rather small minority.

FLATOW: But it's got to be difficult to do a case-controlled experiment, right, on real people and real families?

KLUGER: That's exactly right, and that's one of the concerns. But again, that's a concern of all social and anthropological and psychological sciences, that they don't have the empirical neatness of physics or chemistry. So you do have to do more studies. You have to build up a massive body of work before you can begin to say correcting for all of the other variables.

That's also one of the reasons siblings, sibling research used to turn scientists off because the variables are so numerous. There's gender. There's age. There's age gap. There's the number of siblings. There's income. There's culture. There's education. There were just too many X factors.

FLATOW: Here's our number, 1-800-989-8255, talking with Jeffrey Kluger, author of "The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us." Here's an interesting tweet from MotherlodeBeth(ph), who says: My brother is 17 years older than me. So I was raised as an only child.

KLUGER: And that's a great observation, and that often does happen, that the gap becomes so big that your older sibling is effectively an uncle or aunt. We have some friends - my older daughter has a friend who's her age, 10 years old, and she has two older brothers who are 24 and 25. But, you know, their parents just decided to have a third child, and they're very much her sort of de facto uncles.

FLATOW: Let's go to David in Birmingham, Alabama. Hi, David.

DAVID: Hello, thank you for having me on. I'm a first-time caller, listen to your show all the time.

FLATOW: Thank you.

DAVID: When I heard today's subject, my ears particularly picked up. I'm the oldest of three boys. My parents divorced when I was 11, and then I picked up a stepsister, and then my dad and his wife adopted three additional children. So my kingdom went from the oldest of three to the oldest of seven.

And you talk about resolution conflict, and the things that you have to learn growing up - I feel like I'm a much more successful adult in dealing with my adult relationships now due to the unique dynamics of my childhood siblings.

I'm on my second marriage to a single child, and it's just been really interesting, especially with this new marriage, the fact that, you know, when she comes to my family reunions, well, we have a lot of people. When I go to hers, you know, it's basically her and her parents.

I guess I was just wondering: Do you see a lot of conflict, or are you aware of a lot of conflict in your studies, between those people who have married into a family with lots of siblings?

FLATOW: All right, thanks for the call.

KLUGER: There doesn't seem to be a lot of conflict in that area. You're absolutely right, though, that kids who grow up in a single-child playroom and kids who grow up in a multiple-child playroom tend to have different approaches to the world and tend to have somewhat different conflict resolution skills.

But the idea of the extended family is a very powerful one and often works, particularly when sibs have been disparate, to pull them back together. Now, you see this a lot in situations in which siblings have drifted, but suddenly there's a whole passel of next-generation cousins, and the gravity of those cousins tends to pull the families back together as well.

So you see the salutary benefit of a later generation in healing old sib differences.

FLATOW: We've had a - he brought up the only child. We've had a lot of questions come in, tweets come in about only children. Tell us something about them.

KLUGER: Well, there's a whole chapter in the book devoted to the two far ends of the sibling relationship: multiple births and only children. G. Stanley Hall, a psychologist at the beginning of the 21st - 20th century, infamously said being an only child is a disease in itself. And that kind of wrongheaded thinking informed psychology for a long time. There have been a wealth of studies since then, and they've shown a few things. First of all, it is obviously true that you get a kind of socialization in a multi-child playroom that you don't get in a single-child playroom.

However, there are so many compensating variables now in a culture in which two-income households are much more common. Both parents are working. There's no full-time mom at home. So kids are winding up in daycare when they're four and five months old. Both of my daughters were. So they get socialization there. We lament the idea of the overscheduled child who, you know, finish his classes at three in the afternoon, but isn't home from soccer and swim and chess club until six.

Well, yes, we should look at how heavily we're scheduled in our kids. But for only children, that's three more hours of socialization in which that kid learns outside the home when he's not learning in the home. That's not to say it's easier. It is to say that the compensating factors are there. It's also important to note that single children tend to skew higher in a lot of qualities we value. They tend to have better vocabularies. They tend to have a more sophisticated grasp of current events. They tend to have more sophisticated senses of humor, all because they're living in a home in which they're outnumbered by adults two-to-one.

FLATOW: And as far as leadership, if I recall, I'm just going off my memory from the old astronaut days. Weren't the early astronauts - tended to be single children?

KLUGER: Well, I think 21 of the first 23 astronauts were either firstborns or only children. And, you know, firstborns and only children get a lot of the same benefits.

FLATOW: Is there - did you find any research, people - they set out to plan their family in advance. Is there an optimum number of children for them to plan for?

KLUGER: There really isn't. Again, nature says the optimum number is 50. And if you can have...

FLATOW: Fifty?

KLUGER: ...51 - well, because nature just wants genes. They just, you know...


KLUGER: ...reproducing is a genetically narcissistic act. So all you want to do is get as many genes as possible across to the next generation. For the kids themselves, it's all about - it's also about survival. But in this case, it's about competing for precious resources - food, love, attention from mom and dad. You know, if you've got 10 chicks in the nest and mom only has nine worms, someone's going to go hungry. If mom only has five worms, you're in big trouble, which is one of the reasons that we're so hardwired for sibling competitiveness. And it's one of the reasons we all jostle for attention.

FLATOW: Mm-hmm. 1-800-989-8255 is our number if you'd like to talk about siblings in the few minutes we have left here. We're talking with Jeffrey Kluger, author of "The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us," on SCIENCE FRIDAY, from NPR. I'm Ira Flatow, heading over to the phones. Let's see if we've got - we've got an interesting caller, from - Michelle in Merced, California. Hi, Michelle.

MICHELLE: Hi. It's really exciting to speak with you.

FLATOW: Well, thank you. It's exciting to talk to you, too.


FLATOW: Go ahead.

MICHELLE: My question was actually, when you started describing - I'm the youngest of two siblings. I have an older sister of three years. And when you just started describing the traits of the older sibling, I realized that we're almost the exact opposite of what you described. I'm taller. I actually have a much better career. I'm much closer to the family. And I would actually describe us having a rather toxic relationship. We can barely be in the same room together.

But when my father remarried, I actually gained two step-siblings, an older sister and an older brother by about 12 to 15 years. And I find I'm much, much closer to them, like I can call them on the phone. I can spend holidays with them. And I was wondering if you found anything in your research that maybe described the relationship of a younger sibling not having a good enough relationship with their blood sibling and, like, attaching to a step-sibling.

KLUGER: Sure. There's a lot of research that touches on all those things. First, keep in mind that, you know, the science behind this is - it's hard genetic science. It's hard behavioral science. And in that sense, we all come with essentially the same software preloaded. But layered on top of that - in human beings, as opposed to in other animals - there's a whole suite of other factors in play. There's compassion and there's anger and there's tenderness and there's resentment. And there are all the other things that can confound the underlying rules.

So there are plenty of exceptions to these rules, which is why it doesn't surprise me that by no means does every birth order - or birth order of traits consistent across families. In terms of finding that kind of kinship in step-siblings, that's very common, and a very healthy compensation that - that people come up with. Only children, for example, will tend to find sibling kinship in their cousins.

They'll gather a group of de facto siblings around them. Step-siblings can be - can serve an equivalent function, both when kids are only children, and when they have fraught relationships with their blood siblings. In addition, step-siblings and families - now, your case is a little bit different, because the ages sound a little bit off. But step-siblings and families, if that family is fused young enough and the family can survive a good threshold - it's about six years - if the family can survive six years or so, the difference is that separate a step-sibling from a real sibling tend to vanish entirely. And, in fact, step-sibling relationships can be a little less challenging, because they don't have that early-life competition for the resources of the same parents.

FLATOW: All right...

MICHELLE: What would you say would be young enough to have that fusing between the sibling and the step-sibling?

KLUGER: Well, again, any age. I mean, if you - if the kids are young enough that they're going to get a good six years in one another's company, that's usually a good cutoff point. But remember, anything that happens very young, kids are more impressionable. Young kids don't need as much from a new parent, as long as the new parent loves them and shows them attention and is willing to get goofy with them, they'll fall in love with that new parent. So the younger they are, the better they are. But figure 12 is the upper limit of where you want to begin introducing these things.

FLATOW: All right. Thanks for calling. Was there - about a minute left. Any quick surprise you found when you - about yourself when you did research, something that jumped out?

KLUGER: Well, I think one of the things I found was - had to do with my half-brother and half-sister. We didn't meet them. I knew they existed. But we didn't get to know them until my full brothers and I were in our 30s, and they were in their 20s. And I never would have thought that with all of the deep, deep immersion I had and all the challenges my brothers and I went through together, that I would have been able to forge anything like that level of intimacy with my half-brother and half-sister. And we have. That was about 20 years ago. And, you know, as I said, the step-sibling and full-sibling lines can separate and - or it can begin to vanish, and so can the half and full.

FLATOW: Well, thank you, Jeffrey, for coming in. Great book. Jeffrey Kluger's book "The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us." We're going to take a break. And when we come back, we're going to talk about, oh, how to join a club to make anything you want to. So stay with us. We'll be right back after this break.

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