This blog is intended to go along with Population: An Introduction to Concepts and Issues, by John R. Weeks, published by Cengage Learning. The latest edition is the 12th (it came out in 2015), but this blog is meant to complement any edition of the book by showing the way in which demographic issues are regularly in the news.

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Saturday, September 23, 2017

Older Fathers Put Their Children at Higher Risk of Genetic Diseases

One of the odd things about human reproduction is that women are fecund (capable of bearing a child) from puberty in the teens to menopause in the 40s, whereas men are generally capable of fathering a child from puberty until death at any age. It is well known that as a woman gets older, especially in the late 30s and early 40s, the chance of trouble with a pregnancy and the risk of genetic disease for her baby increase. Men have rarely been implicated in these issues, but today's Economist Espresso links us to a research report published this week in Nature.
Increasingly, scientists are finding that men have something similar, with babies born to older fathers more likely to have genetic diseases. A paper published in Nature this week puts some startling numbers to that idea. Researchers studied the genomes of 1,500 Icelandic couples and their children, finding that a child born to 30-year-old parents would have, on average, 11 mutations from its mother, but 45 from its father. And while every year of maternal age adds 0.37 mutations on average, the rate for men is four times higher.
And here's another interesting conclusion from the researchers:
Moreover, the regional excess of C>G variation in humans is largely shared by chimpanzees, less by gorillas, and is almost absent from orangutans. This demonstrates that sequence diversity in humans results from evolving interactions between age, sex, mutation type, and genomic location. 
We probably wouldn't give this very much thought were it not for the pattern in much of the world for couples to delay childbearing. Low fertility in a society is almost always associated with a later average age at parenthood for both women and men. While women have been aware of the risks associated with later childbearing, men have generally not given this much thought with respect to their own age. This research suggests that men should start making these calculations as they get older. 

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