The tick-tock of the biological clock rings in the ears of many women as they approach their mid- to late thirties and into their forties. For some, the sound is deafening and anxiety-inciting. For others, it barely resonates until someone else, ruefully minding your business, brings it up. Regardless of how each woman views it, the term “biological clock” has become so sex-specific as to make “female” an unnecessary prefix. All the while, men generally feel unburdened by a clock—so long as a man gets around to it before he can cash his first Social Security check and can find a willing mate, the kids will come, and his lineage shall be strong and plentiful. Or so it was once thought.
It would be unfair if it were true. The biological bell tolls for both women and men, albeit in different ways. Whereas women are at greater risk for infertility and giving birth to babies with Down syndrome as they age, men over thirty-five face an increased likelihood of bearing a child with abnormalities. Several papers produced by researchers from the United States and the United Kingdom suggest that the older the men are, regardless of their socioeconomic status and the age of the mother, the more likely they are to conceive children with autism, bipolar disorder, and schizophrenia.
Men on the Clock
While all of this research might be novel, its concepts are not. As early as 1912 scientists (the first being a gynecologist by the name of William Weinberg, a huge contributor to the field of genetics) proposed a link between birth disorders and the increasing age of the father. By 1955, L.S. Pearson codified the idea: his copy-error hypothesis stated that sperm were much more likely to experience mutations than eggs, thereby leading to increased likelihood of birth defects attributable to the father’s older age. Leading geneticist James F. Crow explains why males have a higher mutation rates than females in his 1997 review in the Proceedings of the National Academy of Sciences:
“The most obvious explanation lies in the much greater number of cell divisions in the male germ line than in the female germ line. In the female, the germ cell divisions stop by the time of birth ... In the male, cell divisions are continuous and many divisions have occurred before a sperm is produced.”
In short, the older a man, the more mutations his sperm has gone through, and the greater the likelihood for passing along on mutated seed. Seeing as almost all mutations are deleterious, i.e., not good for human survival, that silver fox isn’t about to spawn some superhuman. While Crow acknowledges that the instance of extra-chromosomal mutations “is strongly associated with the mother’s age,” he is more concerned that these paternally-linked gene mutations “are much more frequent.”
At Any Age Possible
The real question: why hasn’t this taken hold of our culture and changed our views regarding May-to-December romances? There appears to be an undercurrent of resentment toward research that casts light on the risk of older men conceiving children. You can look no further than the coverage by the popular press and the reaction to a recent study published in the Public Library of Science in March whose conclusion stated, “The offspring of older fathers show subtle impairments on tests of neurocognitive ability during infancy and childhood.”
A small, but significant, backlash ensued. As soon as it was blogged about on the New York Times, readers felt compelled to share their anecdotal evidence that unequivocally demonstrated that they, as sons of older fathers or their children, never showed signs of intellectual impairment. No, in fact, they and their progeny flourished above those children born to younger parents.
When looking at the results of the study, it becomes apparent that the media struck a nerve. The response exceeded the magnitude of the findings. These researchers determined that children born to men in their fifties had Intelligence Quotients (IQs) measuring a full six points lower than those born to men in their twenties, regardless of the mother’s age. When they accounted for the routine variables, e.g. socioeconomic status, that difference shrank to two points. Now this wasn’t a small study—results came from 33,000 children—so the difference is unlikely due to poor sampling. But it’s reasonable to say that two IQ points are negligible. Moreover, it’s difficult to translate that sort of difference into later-in-life outcomes; the finding only existed for children up to seven years in age. Most people were disinclined to discuss the study and relied on their experiences to disprove the study’s findings.
Is this reaction, in part, due to our culture’s chauvinistic tendency to justify men’s behavior and repudiate women’s? Or is this our inherent frailty speaking? As a society we love the idea of potential (example: our children), but we hesitate to acknowledge limitations, especially if those come about by life choices we have made, such as waiting until fifty to have children. I certainly don’t have any answers, but I’ll ask my old man if he has any ideas.