At cross purposes

The Houston Ship Channel is a rubbish home for a fish. It’s one of the busiest ports in the world and all that traffic has made the water slick with toxic chemicals. Yet the Gulf killifish has found a way: it has evolved pollution resistance by cross-breeding with a different species, the Atlantic killifish, which happened to have a handy mutation.

Cross-breeding, or hybridisation, is more common in nature than we used to think and as global heating makes animals move to areas with lower temperatures, more species may get thrown together. In Alaska and Canada, people have already spotted grolar bears, the result of grizzlies moving up into polar bear territory to escape the heat.

Recently, conservationists have proposed