Sibling Rivalry 

The Revolution Begins at Home

Five years ago, in his book Born to Rebel, Berkeley science historian Frank Sulloway presented some intriguing findings about the relation between personality and birth order within the family. Over the course of 26 years of research, Sulloway found that in pivotal historical moments of socially significant revolutionary change, whether in science, politics, or religion, laterborns were far more likely to favor change, and firstborns far more likely to resist it. Looking at the history of the West, laterborns were 18 times more likely than firstborns to champion radical political revolutions, 48 times more likely to suffer martyrdom in the Protestant Reformation, and 17 times more likely to support radical scientific revolutions during their early stages when the scientific evidence was not yet definitive. And among pre-Darwinian scientists, laterborns were 124 times as likely to support radical innovations.

At least in the West, major revolutions of social import bring out certain aspects of personality that strongly correlate with birth order. Taking his cue from Darwin, Sulloway argued that children come into the world desperately seeking the love and care of their parents--and that firstborns and laterborns find themselves in dramatically different situations in terms of seeking that care. To understand the sources of the roughly fifty percent of personality not governed by genetic influences, Sulloway argues, we must think less in terms of traits and more in terms of family survival strategies that later become enduring features of personality.

Laterborns enter their families as second-class citizens, lacking the rights of their more powerful older siblings, who are bigger, know more, and have already begun to fill up niches to gain parental approval. Laterborns are motivated to struggle for better rights and more power; they oppose the status quo and must find a niche that is not already taken by older siblings. Firstborns, by contrast, have an interest in maintaining the status quo and maintaining the parental investment that their younger siblings threaten; they are more identified with their parents, sometimes acting as surrogate parents to their younger siblings.

In fact, Sulloway found that firstborns who support radical change are likely to have experienced substantial conflict with their parents.

Firstborns have less of a struggle to find a family niche, and their superior size makes physical aggression and assertiveness a more functional strategy. Laterborns must engage in more agreeable manipulations to gain power; on average, Sulloway found that laterborns are more open to experience, less conscientious, more agreeable, and more extroverted than firstborns.

In the wake of Born to Rebel, personality psychologists claim that Sulloway vastly overstates his case. They note that when subjects are asked to describe themselves, birth-order differences are small. Sulloway retorts that if individuals are measured alone on personality traits, without sufficient attention to the behavioral context, birth-order differences are indeed small. But if researchers ask subjects to compare themselves with their siblings on the same traits, birth-order differences in personality come through loud and clear.

Now 54, Sulloway (a laterborn) is something of a maverick in academic circles. He graduated summa cum laude from Harvard and was chosen to be a member of Harvard's Society of Fellows, a coveted position that frees promising students to pursue their own interests. Since receiving his PhD in the history of science from Harvard in 1978, Sulloway has remained on the edge of academia, working from grants and fellowships. The recipient of many awards, including MacArthur and Guggenheim fellowships, he spent most of the '90s affiliated with MIT's Program in Science, Technology, and Society, and is currently a visiting professor at UC Berkeley's Institute of Personality and Social Research, where he teaches a course on evolutionary psychology. We met for the interview at his office in the Berkeley psychology department.

Timothy Beneke: What was the reaction to your book?

Frank Sulloway: The major critiques came from those researchers in personality psychology who had worked on birth order using surveys in which the subjects self-report. When subjects fill out the surveys themselves, birth-order differences seem considerably smaller than they are with historical samples, or with life stories of contemporary individuals.

So there was a battle line set up with some psychologists effectively saying, "When we go and measure birth-order effects using self-report, we don't find much, and yet you have made all these impressive empirical claims." I became very interested in trying to figure out what was going on, so I began designing surveys of my own. The first point I realized is that there are more than 2,000 studies already published on birth order, so it was pointless to duplicate research that had already been done. Instead, we needed to ask what might have been missed in the previous research. One pertinent observation that struck me about asking people to describe themselves on self-report personality tests is that generally there is no effort to compare the person with his or her own siblings.

So I designed a series of surveys where I asked people to rate themselves and a sibling. When you do that, you obtain all the personality differences that I had both posited and documented in my book. So, within families, siblings definitely judge the firstborn to be more conscientious than the laterborn. The firstborn generally occupies a niche as a surrogate parent; and that niche, and its associated strategies, is reflected in firstborns being more responsible, organized, self-disciplined, and so forth. Laterborns, who have less power, are seen by themselves and their older siblings as employing more agreeable, low-power strategies, so they score higher on traits related to agreeableness. Laterborns also score higher in openness to experience. In my book, I posited that firstborns are more open in the sense of being intellectual or smart, but laterborns are more open in the sense of being untraditional. These two differences show up in within-family comparisons. Finally, laterborns are seen as being more extroverted in the sense of being sociable, fun-loving, and gregarious. By contrast, firstborns are seen as being more extroverted in the sense of being assertive or dominant--traits that relate back to their greater size and power within the family.

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