The Y chromosome has disappeared in at least one species of mammal, the Transcaucasian mole vole. Mole vole females are still XX, but the males are plain X (sometimes called X0), with one fewer chromosome. Given that they’ve lost the Y-chromosome DNA that turns embryos into males, it’s a mystery how the voles still manage to produce any males. But say that human Ys did go extinct, and men with them. Would human reproduction cease? Perhaps not, considering that we have the ability to freeze sperm nowadays and could stock up; we’ll probably be able to genetically engineer sperm in the future anyway. Or if we got evolutionarily lucky, perhaps women would develop a mammal version of parthenogenesis, which allows reptile and fish embryos to develop from unfertilized egg cells. Regardless, there’s no need to be scared, guys—don’t expect some Children of Men–like plummet in fertility. Any changes to the Y could take place only over millions of years.