Scientific hypotheses from 1956

This article was from the Guardian:

Intelligence tests recently carried out among more than a thousand children in Wolverhampton schools appear to show a striking and quite unexpected increase in the mental capacity of children born since 1945. A psychiatrist concerned in the tests has suggested that the most probable hypothesis to account for this change is the effect on the brain of the increase in "background radio-activity".

For the pointer I thank Michelle Dawson.