The article Explaining the Relation Between Birth Order and Intelligence by Petter Kristensen and Tor Bjerkedal (appearing in the journal "Science") seems to have got quite an amazing amount of press so I thought I should say a few words about it. I did not make any comment initially because I thought that it raised no new issues and was not in any way surprising.
To recap briefly, the authors did some very clever statistics on data from Norwegian army recruits which show pretty clearly that being a firstborn raises your IQ by a few points.
I think the reason the article has got such a lot of attention is that the political Left seizes on environmental causes of intelligence like a thirsty man in a desert. All the evidence is of an overwhelming genetic influence on IQ so anything that appears to "undermine" that will be highlighted -- given the traditional but vastly counterfactual Leftist belief in the infinite plasticity of human characteristics.
But the Norwegian findings don't in fact undermine anything. Although IQ is one of the human attributes that is most strongly influenced by genes, nobody has ever claimed that genes alone do the trick. It has always been known and asserted that environmental factors have a subsidiary role -- and stimulation in early childhood has long been agreed to be one of those subsidiary factors.
And firstborns get more attention and hence most stimulation. So a small advantage from being a firstborn was always to be expected.
Perhaps the most amusing part of the coverage given to the findings is the way that old scientific fraud, Frank Sulloway, has managed to insert himself into the discussion. Sulloway is a great advocate of birth order as an influence on human behaviour so I suppose it had to happen but Sulloway's own theory is that birth order determines your politics and, among social scientists, I think it is only the credulous who believe that these days. Sulloway's sustained attempts to block publication of evidence contradicting his theory probably tell you all you need to know about that.
Just a footnote: Did you know that your politics are even more heavily determined by your genetics than is how tall you are? Some people (Leftists) are just born crybabies. See Eaves, L.J., Martin, N.G., Meyer, J.M. & Corey, L.A. (1999) Biological and cultural inheritance of stature and attitudes. In: Cloninger, C.R., Personality and psychopathology. Washington, D.C.: American Psychiatric Press. Pesky things, those genes!
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