In barstool speculation on how long it's possible for someone to survive without sex, the phrases "old fossil" and "a million years" certainly do turn up. However—meaning no disrespect to snubbed Homo sapiens—our species doesn't even register in the scientific version of the debate. In this, there are genuine geologic fossils. And a million years? Forget it. The species attracting interest now look as if they may not have had sex for tens, or even hundreds, of millions of years. Yes, there really is a scientific version of the barroom lament, and it's a serious inquiry. Biologists have long held...