Nature: Big Birds Can't Fly

The ostrich, the emu, and the rhea–together with the kiwi and the cassowary–are the court jesters of the avian world, because they can’t do the one thing that birds are famous for doing. They can’t fly. But exactly how, and why did these birds abandon flight? It’s been one of the natural world’s great mysteries. And now DNA is promising to give us the answer.