<Li> While much of the rest of the world underwent significant cooling and thus loss of species diversity, Australia--New Guinea was drifting north at such a pace that the overall global cooling effect was roughly equalled by its gradual movement toward the equator . Temperatures in Australia--New Guinea, in other words, remained reasonably constant for a very long time, and a vast number of different animal, fungal and plant species were able to evolve to fit particular ecological niches . </Li> <Li> Because the continent was more isolated than any other, very few outside species arrived to colonise, and unique native forms developed unimpeded . </Li> <Li> Finally, despite the fact that the continent was already very old and thus relatively infertile, there are dispersed areas of high fertility . Where other continents had volcanic activity and / or massive glaciation events to turn over fresh, unleached rocks rich in minerals, the rocks and soils of Australia--New Guinea were left largely untouched except by gradual erosion and deep weathering . In general, fertile soils produce a profusion of life, and a relatively large number of species / level of biodiversity . This is because where nutrients are plentiful, competition is largely a matter of outcompeting rival species, leaving great scope for innovative co-evolution as is witnessed in tropical, fertile ecosystems . In contrast, infertile soils tend to induce competition on an abiotic basis meaning individuals all face constant environmental pressures, leaving less scope for divergent evolution, a process instrumental in creating new species . </Li> <P> Although New Guinea is the most northerly part of the continent, and could be expected to be the most tropical in climate, the altitude of the New Guinea highlands is such that a great many animals and plants that were once common across Australia--New Guinea now survive only in the tropical highlands where they are severely threatened by overpopulation pressures . </P>

Australia is the only country that is also a continent