Because of the great scale on which World War II (WWII) was fought, national armies could not afford to rely on their traditional recruitment methods, and therefore often had to resort to drafts to select their combatant forces. This means that all sorts of people ended up in the military, including very smart and very dumb designated patriots.

Scotland was among the only countries at that time to have made its citizens take a mandatory IQ test, in 1932 for those born in 1921, which offered the central government a clear perspective on the level of education present in the population at the time of the war. Now, scouting through the de-classified archives, researchers at the University of Edinburgh, led by Ian Deary, showed that some of the most intelligent men to have fought in the war on behalf of Scotland died in battle, while others, who were less intelligent, returned home unharmed.

"No other country has ever done such a whole-population test of the mental ability of its population," Deary says. "We wonder whether more skilled men were required at the front line, as warfare became more technical."

"We also wondered whether there was an overall small tendency for more intelligent soldiers to want to do the job well, perhaps meaning they ended up in more threatening situations," he adds.

The find was further strengthened by the fact that Scotland registered an abrupt drop in the levels of intelligence of its men, soon after the war completed, until the next generations of children grew up to replace their fathers.

"One could hypothesize that the association between greater intelligence and higher war-related mortality might be driven by the more crystallized verbal abilities, leading to greater leadership roles," adds Phil Batterham, an epidemiologist at the Australian National University in Canberra, Australia.