I was more than a little shocked when Steven Pinker stated point blank that birth order does not affect personality. It was a little more than a page or two in his long The Blank Slate, but it was the part that most stuck with me. Not long after reading that, I came across a chapter collected by Gary Marcus making the same argument. In essence, the argument was that study after study had failed to find any empirical evidence of birth order effects.
(Full disclosure: I have known Gary Marcus for some time, and his early work was a spring-board for my first published paper. I have met Pinker only a few times, but he was the PhD mentor of my first cognitive science mentor, Michael Ullman.)
I didn’t believe a word of it. But, as they say, “them’s the results.” There has been some success in finding a birth order effect on IQ, with IQ dropping a little with each child. A recent mammoth study replicating these results got a great deal of press. Still, that’s not really an effect on personality, which is what interested me.
This is not as esoteric a point as it may seem. There is a lot riding on it. The reason Pinker brought up birth order in his “The Blank Slate,” was that it is a test case in the Nature vs. Nurture debate. Specifically, what affect do parents and the familiiy environment have on children as adults? That’s a hard question to test, because it’s hard to quantify “family environment.” But birth order is easy to quantify. Pinker argues that family environment and parent child-rearing strategies are fairly irrelevant. The lack of birth order effects on personality lends strong support.
As I read the literature on birth order effects, I started to wonder if the problem was with quantifying “personality.” These studies all hinge on having a good measure for “personality,” otherwise you can’t say that people of a similar birth order are similar in personality. I began to think I had a way around this problem, and I developed an experiment. I ran two versions of the experiment on undergraduate psychology students at Central Michigan University, and it showed weak but significant birth order effects. Undergraduates at a single school is a fairly limited sample, so I’m running a larger version of the same experiment through the Web.
You can participate by clicking here: Birth Order Study.
In a few weeks, I hope to do a more detailed post on this topic.
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