A number of bacteria that infect insects have a simple and brutal way of increasing their transmission: they kill off all the male progeny of the females that they infect. There’s actually some evolutionary logic to this. The bacteria can get transmitted to the eggs of the females they infect but can’t get carried along on the sperm. That makes the male offspring a problem: they can’t spread the bacteria further, and they’ll compete with the females for food. Better to kill them off, then, just to ensure that never becomes a problem.

But it’s one thing to have something that’s a good idea conceptually and another entirely to evolve an implementation that gets the job done. How, exactly, do you go about killing one sex while leaving the other untouched?

Thanks to a lucky accident, two Swiss researchers (Toshiyuki Harumoto and Bruno Lemaitre) have identified the gene that allows one species of bacteria to kill off males. Although we don’t have all the details, it’s clear that the system leverages something that male flies need to do to cope with the fact that they only have a single copy of the X chromosome.