UNLIKE women, men can continue having children into old age, but those kids may pay a small price – in intelligence.
Children born to older dads score lower on average on a range of tests, including concentration, memory, reasoning and reading, while the kids of older mothers score higher than those of younger mothers. That’s according to at the University of Queensland in St Lucia, Australia, and colleagues, who analysed data on more than 33,000 US children taken at 8 months and again at 4 years and 7 years (PLoS Medicine, ).
One might expect the offspring of older parents to benefit from good nurturing and better opportunities, leading to higher IQ, says McGrath. “That is exactly what we find for mothers – but exactly what we don’t find for dads.” The differences in test scores were small, however, amounting to 2 IQ points for the child of a 20-year-old father compared with that of a 50-year-old.
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Accumulations of genetic errors in sperm-producing cells may explain these results, says McGrath, as well as findings of an increased risk of schizophrenia, autism and bipolar disorder in the children of older dads.
