I'm intrigued that the stated IQs seem above-average (100):
"In the study, Norwegian epidemiologists analyzed ... military records. ... the researchers found that eldest children scored an average of 103.2, about 3 percent higher than second children (100.3) and 4 percent higher than thirdborns (99.0)."
Especially considering that there will always be more first-borns than second- and third-borns. I'm not sure if the bell-curving is done internationally, but I would bet it is - otherwise it would be useless as a measure of intelligence between different nations. So the difference would be explained if Norway has a slightly higher IQ than average.
"In the study, Norwegian epidemiologists analyzed ... military records. ... the researchers found that eldest children scored an average of 103.2, about 3 percent higher than second children (100.3) and 4 percent higher than thirdborns (99.0)."
103.2 more than compensates for 99.0.
Since Norway has mandatory military service http://en.wikipedia.org/wiki/Military_service#Norway , this does not refute jokes about "military intelligence".