There are places where frogs could be — but aren't. Ninety years ago, scientists were debating the question of animal dispersal. How come there are kangaroos in Australia, and none in southern Africa ...

There are places where frogs could be — but aren't. And places where frogs could be — and are. Ninety years ago, scientists were debating the question of animal dispersal. How come there are kangaroos ...

There are places where frogs could be — but aren't. And places where frogs could be — and are. Scientists in the 1930s hadn't yet come up with the notion of plate tectonics (that continents break up ...