Papua New Guinea: Most Diverse People

This Science Monday comes from the journal Science.  You can't get much more sci ency than that.  Except for maybe Nature.
If you travel through New Guinea, it is apparent to the trained ear that people along the banks speak distinct languages. The island's remarkable linguistic diversity reflects real genetic differences.  The report in Science concludes that this genetic variation dates back just 10,000 to 20,000 years, rather than to 50,000 years ago or so, when humans first arrived.
The island's independent invention of agriculture 10,000 years ago did not wipe out the genetic differences, as it did in Europe or parts of Asia. With agriculture, you tend to get larger groups of people and genetically homogenized societies. In Europe, farmers from Anatolia replaced local hunter-gatherers and erased much of their genetic contribution. That did not happen on New Guinea .
The researchers analyzed variation among 1.7 million DNA markers across the genomes of 381 Papua New Guinea (PNG) residents, and they also compared the complete genomes of another 39. They concluded that the people of New Guinea were isolated from Asians for most of prehistory, and that highland and lowland dwellers separated from each other 10,000 to 20,000 years ago. In the highlands, people split into three very distinct clusters of social groups within the past 10,000 years, soon after they began cultivating plants. In the lowlands, two main clusters arose in the north and south.  Why the separation?  That is one for the anthropologists to answer, but it is not solely geographic separation.  Cool right?