However, about half way through the author writes
> The only place on the whole island where the two worlds nearly collide is the Markham valley […]
Author then goes into a bit of detail on that place before giving two reasons why he believes “that”. Two reasons I cannot for the life of me parse
> The reason why I believe that, despite the minimal trade that existed, the highlands were functionally cut off, is that when the Europeans occupied New Guinea, they themselves did not ever speak of or show knowledge of the highlanders. Similarly, when the highlanders first encountered Australians, they had no concept of the coastal people, or where the shells came from, or any further concept of the broader world.
So the reason the highlanders world nearly collided with the coastal dwellers at Markham Valley is because the Europeans didn’t meet the highlanders when they occupied the island?
The other reason is to do with genetics, which I find equally detached from the core subject of those paragraphs.