When it comes to reproduction, female biology is often described in terms of a ticking clock. Women are born with most of their lifetime supply of eggs, meaning that a woman’s age is usually the same as the age of her eggs. Older women therefore produce older eggs.
But male reproduction works differently. Sperm are produced continuously from puberty onwards and can be stored in the reproductive tract before ejaculation. That means a man’s age is not necessarily the same as the age of his sperm. So what happens to sperm while they wait?
Men trying to conceive are often advised to remain sexually abstinent for several days to allow their sperm count to build up. It is true that abstinence increases sperm count. But the size of the ejaculate is not the only factor that determines fertility. Our new study shows that in men (and other male animals), sperm stored during sexual abstinence actually “ages” and deteriorates in quality.
