Six on Geography and Science: What Happens If We Hit Sperm Count Zero?; How Connected Is Your Community to Everywhere Else in
philip panaritis
"If we are half as fertile as the generation before us, why haven't we noticed? One answer is that there is a lot of redundancy built into reproduction: You don't need 200 million sperm to fertilize an egg, but that's how many the average man might devote to the job. Most men can still conceive a child naturally with a depressed sperm count, and those who can't have a booming fertility-treatment industry ready to help them. And though lower sperm counts probably have led to a small decrease in the number of children being conceived, that decline has been masked by sociological changes driving birth rates down even faster: People in the developed world are choosing to have fewer children, and they are having them later.
The problem has been debated among fertility scientists for decades now—studies suggesting that sperm counts are declining have been appearing since the '70s—but until Swan and her colleagues' meta-analysis, the results have always been judged incomplete or preliminary. Swan herself had conducted smaller studies on declining sperm counts, but in 2015 she decided it was time for a definitive answer. She teamed up with Hagai Levine, an Israeli epidemiologist, and Niels Jørgensen, a Danish endocrinologist, and along with five others, they set about performing a systematic review and meta-regression analysis—that is, a kind of statistical synthesis of the data. “Hagai is a very good scientist, and he also used to be the head of epidemiology for the Israeli armed forces,” Swan told me. “So he's very good at organizing.” They spent a year working with the data."
The Myth of Badass Sperm
We’ve all been taught that human fertilization is an Olympic-style competition. The truth is that it’s much more like a gigantic lottery.
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