Friday, 1 September 2006

Why season of birth is related to childhood intelligence

Countless studies have found that children’s intelligence appears to be related to the time of year they were born in. Some investigators have argued this is because seasonally varying environmental factors like temperature and infections can affect brain development. But now Debbie Lawlor and colleagues have analysed data from 12,150 children born in Aberdeen between 1950 and 1956, and they’ve concluded that the effect of season of birth is almost entirely explained by the age children happen to be when they start school.

Reading ability at age 9 and arithmetic ability at age 11 were both related to season of birth (children born in late Winter or Spring performed better), but this association virtually disappeared once age at starting primary school and age relative to class peers were taken into account. That is, season of birth was only related to later intelligence because it affected the age children started school, with those who started school younger or older than the average tending to score less well on later intelligence tests.

By contrast, the outside temperature when the children were conceived, during gestation, and at their birth, had no independent association with their later intelligence.

“We have found weak season of birth effects on some aspects of childhood intelligence, which appear to be explained by differences in age at school entry and/or age relative to peers”, the researchers concluded.

However, the story isn’t entirely straightforward. The researchers predicted that children who spent less time at primary school would perform less well on subsequent intelligence tests. Instead, they found the opposite pattern. “It is possible that those who had least time in primary school but most time at home were in fact given extra tuition by their parents”, they surmised.

Lawlor, D.A., Clark, H., Ronalds, G. & Leon, D.A. (2006). Season of birth and childhood intelligence: Findings from the Aberdeen Children of the 1950s cohort study. British Journal of Educational Psychology, In Press. DOI: 10.1348/000709905x49700.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.


Anonymous said...


The authors of Freakonomics wrote sometime ago about how being older (than one's cohort) can confer an advantage on kids in younth soccer programs.

Extending their logic to performance in tests of 'intelligence', I can see how being younger than average is a disadvantage. What is puzzling is that being older is also bad! Why might this be? Do the authors give possible explanations? It would be interesting to see them discussed here in this blog.

Many thanks in advance.

Anonymous said...

I think that the season of birth has nothing to do with intelegence.

The main reason why some people are more intelegent, is becouse of the family background and up-bringing.


Anonymous said...

Geeze can't you read?! It's spelled intelligence. Genetics is the biggest factor in intelligence, the rest is egalitarian pseudoscience.

Joe Friendly said...

Humans have apparently evolved to respond to time of year of birth with systematic differences in neural networking parameters of integration as nature's way of increasing the variety of ways of being human in addition to genetics. Most animals have particular seasons of birth characteristic of their species. By humans being born the full variety of times of year human nature has been regarded as mysterious. Birthday helps sort the variety of human natures, as if providing a solar compass for the human domain! Birthday amounts to the dimension of phase of the annual sine cycle of solar energy flow to the Temperate Zones, and therefore a profound index of solar differences in the developing infant's first year's environment. We need to rescue birthday from astrology! It is a big deal!

Post a Comment

Note: only a member of this blog may post a comment.