Previous studies have suggested that the nation’s IQ rises by around three to four points per decade, a phenomenon known as the ‘Flynn Effect’, driven by increased prosperity, nutrition, hygiene and safety.
But researchers were astonished that the jump was so pronounced between the 1920s and 1930s.
“When you consider the life experiences of the two groups, those born in 1921 experienced the depression as teenagers and then World War Two,” said lead researcher Dr Roger Staff.
“Those born in 1936 were children during the war and experienced food rationing. Although rationing meant that the food was not particularly appetising it was nutritious and probably superior to the older group. In addition, post war political changes such as the introduction of the welfare state and a greater emphasis on education probably ensured better health and greater opportunities.
“Finally, in their thirties and forties the 1936 group experienced the oil boom which brought them and the city prosperity. Taken together, good nutrition, education and occupational opportunities have resulted in this life long improvement in their intelligence.”
The University of Aberdeen team examined two groups of people raised in Aberdeen, one born in 1921 and one born in 1936. These people are known as the Aberdeen Birth Cohort and were tested when they were aged 11 and when they were adults after the age of 62. The study consisted of 751 people all tested aged 11 and who were retested between 1998 and 2011 on up to five occasions.
Researchers compared the two groups at age 11 found an increase in IQ of 3.7 points which was marginally below what was expected but within the range seen in other studies. However, comparison in late life found an increase in IQ of 16.5 points which is over three times what was expected.
Professor James Flynn, who discovered the Flynn effect said; “The study is very interesting. It should raise our estimates of British adult gains in intelligence.”
Before the war, more than two thirds of British food was imported. But enemy ships targeting merchant vessels prevented fruit, sugar, cereals and meat from reaching the UK.
The Ministry of Food issued ration books and rationing for bacon, butter and sugar began in January 1940.
One person’s typical weekly allowance would be: one fresh egg; 4oz margarine and bacon (about four rashers); 2oz butter and tea; 1oz cheese; and 8oz sugar.
But it was the MoF’s Dig For Victory campaign, encouraging self-sufficiency, which really changed how Britain ate. Allotment numbers rose from 815,000 to 1.4 million.
Pigs, chickens and rabbits were reared domestically for meat, whilst vegetables were grown anywhere that could be cultivated. By 1940 wasting food was a criminal offence.
As sugar was in short supply, sweets were rationed from July 1942 to February 1953.
It is known that despite the stress of the war, the health of the lower classes improved as they were encouraged to eat vegetables, beans and fruit. Access to cigarettes and alcohol was limited.
“These IQ gains are probably not unique to Aberdeen with similar with similar environmental changes being experienced across the UK,” Dr Staff added.
The research was published in the journal Intelligence.