And this leads to the most interesting part of this story: how the highlanders were so isolated for so long.

I want to acknowledge that the highlanders were not completely, hermetically sealed off from the outside world – it’s just that knowledge of outside world never actually made it to them or vice versa.

Over time, a few goods did make their way up to the highlands: pigs, about 3,000 years ago; the sweet potato, which is South American and arrived about 300 to 400 years ago; and tobacco, also American, which came the same way.

The journey the sweet potato and tobacco took to get there is a good example of how this all worked without transmitting further information. The Spanish and Portuguese brought both plants to the spice islands (in what is now Indonesia), just off the western tip of New Guinea, in the 1500s. The sultanates had been trading with the western tip of the coastal region of New Guinea for centuries. So the plants crossed over and started moving east along the coast and up into the interior. Beyond that point, there were no merchants. But when a woman married into the next clan over, she took cuttings from her family’s garden with her. Each new family then planted the same, saw that it worked, and passed it on. At that pace the sweet potato crossed the highlands in a century or two, with nobody knowing where it came from beyond the tribe beside them.

And what fascinates me is that even with the highlands as sealed off as they were, such significant goods still got in. Sweet potatoes allowed a population explosion in the highlands: they give far more calories per acre, and pigs can live off them. So in a 10,000 year sealed off universe, after the invention of agriculture, the biggest change to highland life happened in the last 500 years, which I guess isn’t a coincidence, as the sweet potato got there through the same structural forces that later brought the Australians.

Here is much more from Daniel Frank, fascinating throughout.