Originally Posted by John DiFool
2-4,000 years seems too recent to account for isolated populations (such as Australian indigents, if that is the right word).
Even 'isolated' populations were probably not truly isolated. They may have, very occasionally (like once every few hundred years), had enough contact with surrounding groups to interbreed. Just imagine a lost baby or adult in the forest, adopted by the 'isolated' tribe (or vice versa), happening every few hundred years thousands of years ago.