Scientists have found an elegant way to disentangle the effects of nature and nurture.
Writing in this week's PNAS Cardiff University researcher Anita Thapar and her colleagues compared birthweights and subsequent anti-social behaviour in 779 children with whether their mothers smoked during the pregnancy. But, cunningly, the study subjects were all children conceived by IVF, over 200 of whom were from donor eggs and hence genetically unrelated to their mothers. This study design meant that genetic factors (nature) could be separated from maternal and environmental factors (nurture).
Maternal smoking has been linked in the past to both low birthweight and subsequent anti-social behaviour, although how it provokes these outcomes nobody knew. But what emerged from the Cardiff team's analysis was a very strong relationship between maternal smoking and low birthweight in both the genetically related and genetically unrelated children. This proves that the effect of smoking on birthweight is not down to genetics but must be due to the toxic effect of smoking itself.
Antisocial behaviour, on the other hand, was only associated with maternal smoking in the children genetically-related to their mothers, but not in the children born using donor eggs.
"This shows the importance of inherited factors in the association between prenatal smoking and and off-spring behaviour," says Thapar. "This suggests that gene-environment correlation is important in explaining this association."
The team point out that their results demonstrate that this original and unusual cross-fostering study design is a highly feasible and informative method with which to separate inherited and pre-natal effects on human health.
"There are a whole host of things we can look at now using the same approach," says Thapar.
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