If they literally never mix, it doesn't reach the population it isn't in. But that's a bigger ask than you'd think. Stuff moves around, on its own, and often,

If they literally never mix, it doesn't reach the population it isn't in. But that's a bigger ask than you'd think. Stuff moves around, on its own, and often, on humans and human artefacts. Like for example, mosquitoes breeding in a puddle on a boat. This is basically a worry people have about gene drives, that they will jump from places where they are wanted, to wild populations that are doing nobody any harm, and eradicate whole species.