Women all know that once they’re getting into their late 30s and beyond they have to step on the gas a bit if they want to have a healthy baby, and older mothers-to-be must agonize over whether or not to test for various congenital abnormalities.
But men can wait as long as they like, can’t they? Rod Stewart fathered his eighth child at the age of 66 after all, Sir Paul McCartney his fourth at 61, and the 54 year-old Simon Cowell has only just produced his first little bundle of joy. Everybody knows that when it comes to having babies, women get past their sell-by date long before men.
Or do they? Actually the news is that guys had better look out since evidence is piling up showing they hold a much bigger share of responsibility than they probably thought for their progeny’s genetic health.
One study, where dozens of Icelandic families had their genomes sequenced has shown that older dads are much more likely to have kids with diseases often linked to new genetic mutations. The researchers estimate that a 36 year-old man will pass on twice as many mutations to his child as a man of 20. Other research suggests that mutations for autism, for example, are four times more likely to originate on the fathers’ side than the mothers’.
It’s not just autism though and a much larger scale, just published study based on Swedish data has linked advanced paternal age with a whole range of psychiatric and even academic problems.
Luckily for the researchers, Brian D’Onofrio of Indiana University and his colleagues, the Swedish seem to be obsessively good at keeping records and the team have been able to sample every single person born in the country between 1973 and 2001 to look at outcomes of their fathers’ age at birth – that’s over two and a half million people.
They found that a child born to a man aged 45 was 3.5 times more likely to have autism, 13 times more likely to have ADHD and 25 times more likely to have bipolar disorder than a child whose father was 24 years old. Children of older dads were also found to be more prone to substance abuse and suicidal behaviour, and less likely to do well academically.
And this is a big issue given that the average age of fathers at the birth of a child is ever increasing, rising from 27 years in 1970 to 33 in 2012, and some have even speculated that this could partly explain the increase in diagnosis in the last few decades of some of these conditions.
Why is it the fathers’, rather than mothers’ age that matters so much? The thing is, women have all their eggs mustered and ready for action from birth, well ready apart from a couple of tweeks anyway, while a man keeps making new sperm throughout his life. This means that mistakes in the germ cell division process accrue and the sperm of older men carry more mutations, some of which could lead to congenital problems in their babies.
The researchers were keen to control for environmental effects and did this by including a comparison of siblings who, unless they’re twins, clearly have a father of a different age when they were born but likely grow up in similar environments. The detrimental effect on outcomes for kids of older fathers remained, although the team concedes that some of the negative consequences of having an older father may be outweighed by his greater maturity, conscientiousness, and social and cultural capital.
So for men, as for women, it’s a matter of weighing up the pros and cons depending on your own life and loves when deciding when to have kids, but these results certainly need taking into account. The reproductive playing field is levelling and it’s clear that the biological clock is not just a woman thing. It’s also definitely a man thing.