The latest twist in the history of humankind is that after ancestral Homo sapiens settled Papua New Guinea, which seems to have been around 50,000 to 70,000 years ago, they not only didn't budge. They not only didn't mix with the peoples around them, if any. They didn't even mix with each other, going by the startling degree of genetic and linguistic diversity found between groups of Papuans, as reported in Science this week.

In fact, the original occupants of both Papua New Guinea and, later, Australia, seem to have been a very sedentary bunch. The aborigines' forefathers reached Australia at least 50,000 years ago, scattered along the coastline for about 1,500 to 2,000 years and then, having struck roots wherever they struck roots, they didn't budge for the next 50,000 years.

An unrelated study published in Nature in 2016 postulated that aboriginal Australians and Papuans diverged from Eurasians anywhere from 70,000 to 50,000 years ago. This postulation is bolstered by the new study, which indicates that the Papuans would remain genetically independent from Europe and Asia for most of the last 50,000 years.

Anyway, some time would pass, then the ancestors of the Papuans and Australians split somewhere between 40,000 to 25,000 years ago. "Papua New Guinea was likely a stepping stone for human migration from Asia to Australia," writes the team.

The ancient Australians settled the coasts, and stayed there. The ancient Papuans would settle the highlands and the lowlands – and each would stay where it was. "The genetic divide is between the people in the highlands and lowlands that appears to have occurred 10,000 to 20,000 years ago, concurrent with the spread of crop cultivation and the trans-New Guinea language family," write the scientists.

Open gallery view Baby tree kangaroo on the shoulder of the chief's wife, Papua New Guinea Credit: Nyctalimon

They would stay isolated, genetically and otherwise, in the highlands and lowlands until around 4,000 years ago. Even more startlingly, the people from the isolated Papuan highlands remain independent now.

This is the conclusion of the first large-scale genetic study of Papua New Guineans, was conducted by the Wellcome Trust Sanger Institute (the British institute previously known as The Sanger Centre), Oxford, and the Papua New Guinea Institute of Medical Research.

Out of Africa

Though the theories of human evolution have been evolving themselves, anthropologists still generally think that all the peoples in the world today originated in a single migration of Homo sapiens out of Africa, perhaps 60,000 to 70,000 years ago. There was clearly one or more Homo sapiens migrations out of Africa, but they failed (went extinct). The people who spread into Asia, walking and/or sailing, evidently reached Papua New Guinea and Australia very early in this process.

Note that sea levels 60,000 years ago were a lot lower than today because so much water was locked up in the ice caps. Africa and Arabia were connected, and the ancients could have walked at least much of the way down along the East Indies coast to Australia, over exposed land that is today covered by ocean.

One reason why scientists had suspected the Papuans might have great genetic diversity within them, is that this small number of 8 million people has about 850 languages (accounting for over 10 percent of the world's total number of languages, the scientists claim). They also demonstrate cultural diversity.

So the scientists sequenced 381 Papuans from 85 of these language groups, checking more than a million genetic positions in each individual genome, and compared them to investigate genetic similarities and differences. They found that groups of Papuans speaking different languages were genetically distinct.

Open gallery view Highlands of Papua New Guinea Credit: eGuide Travel

"Our study revealed that the genetic differences between groups of people there are generally very strong, often much stronger even than between major populations within all of Europe or all of East Asia," lead author Anders Bergström stated.

In Europe and Asia, populations did not generally remain so isolated, if only because hunter-gatherers got around. Once people started farming, somewhere between the early signs of cultivation 23,000 years ago and around 12,000 years ago, they became more settled and mixed less, giving rise to more genetically homogenous societies.

Yet although Papuans also developed agriculture, no such process of homogenization occured.

"Using genetics, we were able to see that people on the island of New Guinea evolved independently from rest of the world for much of the last 50,000 years," stated Dr Chris Tyler-Smith of Wellcome. "This study allows us to glimpse a different version of human evolution from that in Europe and Asia."