Distant Australia as well belongs to our New World of humanity. Its oldest human remains are also those left by clever sapiens, our siblings. Most oceanic islands, like the three seagirt continents, have also never felt the tread of any ancestral species. Big Madagascar and New Zealand were first settled by seafarers from the Pacific only a couple of millennia past, a timescale that overlaps familiar written history. We can offer a plausible explanation.
Primates are land animals.
Even now, at any moment, not as many as one human out of 1,000 is to be found afloat or aloft. Those ancestral folk could not cross the seas during their million years of foraging afoot. The New World was reached overseas only after the eventual appearance of a dynamic younger species, our very own. It was only the sapient men and women who journeyed a couple of hundred centuries ago along icy coasts and inland valleys. So much water was locked ashore as glacial ice that the level of the high seas dropped by hundreds of feet, and many islands were for a while part of the main.