The introspective morality-dump chapters are not my favorites (eg. I find the 'imagine distant descendants' to be entirely useless intuitively, and would prefer versions of the update-now argument which are more like 'decide now how you would update your beliefs based on predictions you make now failing or succeeding, since once they actually fail or succeed you'll be embarrassed & biased'), but oh well let's begin analysis.

A year ago, Dad had gone to the Australian National University in Canberra for a conference where he'd been an invited speaker, and he'd taken Mum and Harry along. And they'd all visited the National Museum of Australia, because, it had turned out, there was basically nothing else to do in Canberra. The glass display cases had shown rock-throwers crafted by the Australian aborigines - like giant wooden shoehorns, they'd looked, but smoothed and carved and ornamented with the most painstaking care. In the 40,000 years since anatomically modern humans had migrated to Australia from Asia, nobody had invented the bow-and-arrow. It really made you appreciate how non-obvious was the idea of Progress. Why would you even think of Invention as something important, if all your history's heroic tales were of great warriors and defenders instead of Thomas Edison? How could anyone possibly have suspected, while carving a rock-thrower with painstaking care, that someday human beings would invent rocket ships and nuclear energy?

This is actually a pretty bad example. The Australians and New Guineans etc. were not necessarily incompetent (witness the boomerang, or the independent invention of the blow-gun), and specifically, throwing-sticks (atlatl) are really fearsome weapons which can throw darts or rocks insane distances more comparable to English longbows than anything else. Throwing sticks for spears were in military use in ancient Greece or Egypt, areas which always had bows-and-arrows.

A better example would be Tasmania and technology it lost, like making fire.

In a land where Muggleborns received no letters of any kind

This would seem to indicate Harry over-estimated the magnitude of his inference in the early chapters about the implication of so few Muggleborns at Hogwarts, but immediately raises the question of what do those lands do with their Muggleborns.

Finally:

She came awake with a gasp of horror, she woke with an unvoiced scream on her lips and no words came forth

Sybil is now definitely the bearer of at least one unvoiced prophecy, and if I'm counting right, at least two - she woke up without speaking in some earlier chapter as well.