Why is Australia one of the most biologically diverse countries in the world?

Question

Why is Australia one of the most biologically diverse countries in the world?

Answer 1

stevian1 is right. australia was once attached to antarctica (gondwanaland) and since separation has been an island too far away from others to be affected biologically. the only newcomers to the land were aboriginal peoples some 60,000 to 100,000 years ago. they are natural conservitors, so until the arrival of colonial settlers the land saw little change except for the natural evolution of the biosphere. unfortunately modernity is a big threat

Answer 2

Millenia of isolation from the rest of the world have left it relatively untouched