Ellis. It certainly would account for the difference between Mungo and Kow swamp fossils. The belief in two or more migrations into Australia was popular years ago but these days the two types are considered to have evolved in Oz. Simply opposite ends of a cline of variation. Unlikely to have such difference on a relatively small continent. The Aborigine languages are usually divided into two groups. Suggests two migrations. Humans seem to have been in Oz by at least 50,000 years ago and probably longer. I'm presuming the first there basically filled the continent and so N mtDNA and C Y-chromosome were first there in spite of M mtDNA having reached mainland SE Asia before them.
Humans didn't get to Melanesia until about 30,000 years ago, presumably because they didn't have the boating technology to get that far until then. There is also no evidence for people in New Guinea until then but that could be through difficulty of fossil preservation. But they could have died out with changing climate and rise of sea level during the slight warming from 50,000 years ago. Cavalli-Sforza does suggest the the sepik/Ramu of NG may be very ancient though. On the above theory of first in best dressed I'd say Y-chromosome K and mtDNA M came in with the next lowering of sea level starting 30,000 years ago.
People from Melanesia and New Guinea look a lot different from Australian Aborigines. But anthropologists have long believed similar-looking people made up the Hoabinhian culture of SE Asia until about 5000 years ago. People from further north replaced and interbred with them from that time. East Timor appears to be partway through this process. This combination spread into the Pacific, evolved into the Polynesians and arrived in NZ a little less that 1000 years ago.
For anyone from America I see I've made a booboo but I can't be bothered editing it. Of course I mtDNA gets nowhere near America. how did that slip in? Might be some there today with much more recent immigrants.
