Are older men's sperm really any worse?

It turns out this problem is surmountable with a simple trick: Observe cases where couples are using donor eggs. There’s no reason that the age of the egg donor would be related to the age of the father (indeed, in the data it typically is not) which means you can examine the impact of the father’s age independent of the mother’s.

Studies that do this — here is one nice review in the journal Fertility and Sterility — tend to find that while semen volume (and, hence, sperm count) does decline with age, there is little overall impact on reproductive success (the ability of the sperm to penetrate the egg, fertilize it, etc.). This is encouraging — but it’s worth noting that while the number of sperm doesn’t matter much when fertilization occurs outside the body, as is the case when using donor eggs or doing in vitro fertilization, it will matter if you’re procreating the old-fashioned way. So more sex may be necessary.

The evidence on autism and other behavioral disorders appears less reassuring. The authors of a 2011 review article in Molecular Psychiatry combined a number of studies comparing children of older and younger fathers (this is called a “meta-analysis”). They concluded that relative to children born to 20- to 29-years-old fathers, those with fathers aged 30 to 39 were 1.2 times more likely to have autism; those with fathers aged 40 to 49 were 1.8 times more likely; and those with fathers over 50 were 2.5 times more likely. The studies used in the meta-analysis were all pretty consistent. They did not all find the same size effect, but virtually all pointed to increased risk of autism with increased paternal age.