Younger siblings are more prone to taking risks. That is a long-standing theory of University of California, Berkeley, evolutionary psychologist Frank Sulloway, who argues this behavior is a reaction to their relative lack of parental attention.
The look-at-me hypothesis makes intuitive sense, and evidence for it was presented in a study of economic behavior last year. But proving its validity to skeptics would require finding a controlled setting where personality traits are exposed in clearly measurable ways — like a baseball diamond.
In a paper just published in the journal Personality and Social Psychology Review, Sulloway and Richard Zweighenhaft of Guilford College use Major League Baseball statistics as evidence that birth order influences behavior. Looking at performance data on 700 brothers who played in the big leagues, they report younger siblings are 10.6 times more likely to attempt to steal a base than their more risk-averse older brothers.
According to their data, “younger brothers were more likely to engage in the risky business of stealing bases; they attempted more steals per game; and they were more likely to succeed in doing so.”
The researchers used base-stealing as their main measure because it is “inherently risky” behavior, with a big potential downside (making an out) and a marginal upside (as advancing a base does not guarantee scoring). In addition, they note that the player attempting to steal is always risking injury, in that doing so “almost always requires the act of sliding into a base, together with physical contact with the player who is defending that base.”
They also found that, compared with their older brothers, younger brothers were also likely to be hit by pitches. This presumably reflects “a refusal to be intimated by pitchers who throw close to the body,” they write.
In that same paper, Sulloway and Zweighenhaft conduct a meta-analytic review of 24 previous studies looking at birth order and participating in dangerous sports. They conclude that second-born children (and those who came after) are 1.48 times more likely than firstborns to engage in a range of potentially hazardous athletic activities, including playing football or going skydiving.
The researchers offer three potential explanations for their findings. One is that differences in levels of risk-taking are simply the “residual byproducts of personality differences developed in childhood.” Another possibility is that the younger sibling learned from the elder’s mistakes, discovering by example “when risk-taking is appropriate and when it is not.”
The third thesis suggests sibling rivalry is at the root of such behaviors. This notion is supported by their finding that “differences in base-stealing proclivities between brothers were significantly larger when the brothers were separated by less than five years, and when they also competed in the same player category.”
So if Cain is at bat and Abel is on first, look for Abel to make a break for second.
