By Paul Ormerod As the share of adults in the UK who are married drops below 50 per cent for the first time ever, economists as well as romantics should be concerned, writes Paul Ormerod The dramatic erosion of marriage in the UK is one of the key social changes of the late 20 and early 21 centuries. Last week, the Office for National Statistics (ONS) published data showing that for the first time the proportion of the population aged over 16 who were married had fallen to below 50 per cent. Just two generations ago, in 1960, the figure was around 90 per cent. The idea that all family structur…