Here's a breakdown of why:
* Australia: Australia's unique ecosystem has different native species like kangaroos and koalas. There was never a natural population of beavers there.
* Africa: Africa has its own diverse set of animals, including hippos and crocodiles. Beavers are not native to this continent.
* South America: While South America shares some similarities with North America, beavers did not naturally migrate there.
Important Note: It's possible to find beavers in some parts of South America and Africa due to human introduction. These are not native populations, but rather the result of deliberate or accidental releases.