WASHINGTON - It seemed settled -- extensive genetic studies had confirmed that the ancestors of all living humans emerged from Africa some 50,000 years ago and either killed off or out-competed all other human-like creatures who settled across much of the world.

But two studies published this week strongly disputed this scenario and reignited the vigorous and often acrimonious debate about where humans come from.

One study, done in Australia, used genetic evidence that suggested ``Mungo Man'' -- a 60,000-year-old skeleton -- is genetically unrelated to the Africans believed to have evolved 150,000 or so years ago and later to have settled the world.

Another, published in Friday's issue of the journal Science, analyzed physical features of early human skulls to suggest there must have been interbreeding among the migrating Africans and resident Neanderthals and even Homo erectus species of pre-humans.