Wednesday, November 23, 2005


Below we see academic "experts arguing about something that they obviously know nothing about. The article is a discussion of the findings in "The cognitive cost of being a twin: evidence from comparisons within families in the Aberdeen children of the 1950s cohort study", by Georgina A Ronalds, Bianca L De Stavola and David A Leon, which appeared in the British Medical Journal of 18 November 2005:

"Twins may be livewires but they are certainly not bright sparks, according to new research showing that they have lower IQs than single children. The study has ignited debate, with some experts claiming the lower IQ is a result of the twins spending less time in the womb and having less room to grow while they are in there. But others have argued that what happens after birth is more important, with twins losing out because they do not have a parent's undivided attention.

"We know there are language problems with twins - it's very difficult for a parent to adequately develop the language skills of two children at the same time," said David Hay, professor of psychology at Curtin University in Perth, who challenged the assumptions of the British research team. Professor Hay said previous research had shown that if one twin died in early childhood, the IQ of the surviving twin reached normal levels, suggesting the post-natal environment - in particular, one-on-one contact with a parent - played a part.

The study, published yesterday, found a five-point average shortfall in IQ among twins compared to single children - and the difference remained apparent even after factors such as the mother's age, the child's sex and the number of older siblings were taken into account. When the twins in the study were aged seven, their average IQ was 5.3points behind the single children in the same family. By the age of nine, it was 6points behind. Girl twins tended to make up the IQ deficit by the age of about 13, which was not always they case with boys.

The researchers who wrote the paper, published online by the British Medical Journal, were sticking with their theory that the "likely explanation" was a shorter gestation. Lead author David Leon concluded that social and economic circumstances could not explain the IQ gap".

These guys must know twins only via columns of numbers about them. Anybody who has helped bring up twins -- as I have -- will know perfectly well what the problem is -- and it is "none of the above". What happens is that twins do not need others for social support as much as singletons do, so they develop language skills primarily to talk to one-another. But because of their similar age and situation, even dizygotic (fraternal) twins tend to understand one-another with a much reduced use of adult language. They to a degree develop a private and largely non-verbal language of their own. So they have much less incentive to develop adult language skills and are therefore slower to develop such skills. And language skills are a central part of IQ development.


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