Numerous studies show that girls reach puberty younger, become sexually active earlier and are more likely to get pregnant in their teens if their father was absent from the home from when they were young. But the usual explanation – that such families are under more stress – is now being challenged by a long-term study of girls in New Zealand and the US, the Western countries with the highest teen pregnancy rates.



Having no father usually means less household income and a greater chance of other disadvantages, such as domestic violence or a depressed mother. According to the stress hypothesis, this triggers some innate mechanism that ensures that girls pass on their genes sooner when times are tough.



If this is the case, the problem of teenage pregnancies in such families could be tackled by relieving the stress, for instance by providing more support for single mothers. But the latest study shows that even when stress is taken out of the equation, an absent father is still associated with earlier sexual behaviour.

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