The model outlined in Guns, Germs, and Steel serves to a great extent as a corrective to ideological theories about the expansion and rise to dominance of European power in the 18th and 19th centuries, before its crest in the 20th. Jared Diamond famously gives a great deal of weight to biogeographical parameters. Charles C. Mann has taken Diamond's wager, and raised him one. But as noted in the comments below the ascendancy of Europeans in a geopolitical sense is only Act I in this drama.
At a certain point early in the 20th century Europeans or people of European descent (e.g., the scions of the white Creoles in Latin American nations where the majority were indigenous or mestizo) were dominant agents across almost the whole of the globe. Even in nations which remained independent, such as Persia or China, European powers were influential, and independence was maintained in part due to rivalries.
But, there is a differentiation here that must be noted. In some regions, obviously Europe itself, but in much of North America, southern South America, parts of southern Africa, and Australia and New Zealand, people of European descent became demographically preponderant. In other areas, such as India, Europeans were unquestionably the ruling stratum, but their longer term demographic impact was to be marginal. Why the difference? As observed by readers the key here is that in some regions where Europeans intruded they filled the vacuum after a demographic collapse, usually induced by introduction of diseases to which the natives were not immune. In the natural course of things one imagines that native populations would have rebounded. And in fact in certain areas they did, such as the highlands of the Andes. But a native rebound would never be possible in a situation where Europeans settled the land.
The highland zones of Latin America are particularly interest because they illustrate the perils and promise of these regions. In the Andes the elevation is such that Europeans exhibited great physiological stress, and it was reputed that women of European descent were simply unable to carry children to term. The historical records make it clear that the collapse of the Inca Empire was preceded by plagues, almost certainly introduced by the Spaniards. But in the centuries after the collapse the Inca cultural system did not disappear. On the contrary, the Inca language, Quechua, became the lingua franca of the highlands, and a post-Inca aristocracy retained a measure of power in this region. Why? Despite demographic catastrophe due to germs, germs, germs, and a lesser extent guns and steel, the Europeans themselves had to face up to the limits imposed by oxygen. In contrast, the highlands of Central America, in particular around Costa Rica, were much more healthful than the coasts. In much of this region, down into northern South America, the coastal regions are populated disproportionately by people of African descent. That is because of the new endemic status of diseases such as malaria, to which Europeans and indigenous people were vulnerable.
We are frankly in our age reluctant to talk about the real biological differences between human populations because of the excesses in this area in the past. But the human geography of the world today is not a function of ideology, but biology! The Scottish attempt to establish a colony in Panama failed for many reasons, but it is clear that the difficulties that Europeans had with lowland tropical climates was one major factor which serves to scaffold the patterns of settlement we do see. The success of European settlement, as opposed to simply colonial dominion, in temperate climates was not a matter of ideology. The Dutch East Indies company sent hundreds of thousands, if not millions (the labor pool expanded out across northern Germany), of young men to man its enterprises in the eastern seas over several hundred years. Though there is a population of mixed-race people who descend from these, their long term demographic impact has been trivial next to the smaller number of Dutch, French, and German pioneers who settled the Cape, and became the ancestors of the Afrikaners. Of course this is the region of southern Africa with a Mediterranean climate, and where the lack of efficacy of the Bantu agricultural toolkit allowed for the persistence of large numbers of Khoisan people down to the early modern period.
Up to this point I've been emphasizing disease. But that's just the most obvious issue. The Bantu likely introduced practice of cattle herding to the Khoikhoi, so those who pushed west toward the Cape could theoretically have switched away from some aspects of their culture to become pure pastoralists. But this does not seem to have happened. In First Farmers Peter Bellwood argues that there is a consistent problem with getting non-farming populations to engage in sedentary agriculture (though pastoralism seems to come easier). Cultural, and perhaps biobehavioral, dispositions are hard to transmit. But there is no reason why switching from wheat to rice based agriculture should be so easy. Argentina's pampas and Australia's Murray-Darling basin were candidates for easy transplantation of European cultural systems, which existed as complex interdependent implicit folkways. In tropical or semi-tropical zones where Europeans settled it seems most often that instead of being primary producers they had to install themselves as the drivers of men, extracting rents in a relatively brute force fashion (e.g., slave capitalism in the South, Caribbean, and northeast Brazil).
Which brings me to New Guinea. Below is a topographical map. You can see that substantial zones of the highlands are at elevations of ~10,000 feet. To no great surprise these highland regions are also the districts with the highest population densities across the island. The whole island of New Guinea has a population somewhat less than 10 million. This is not exceedingly large (Taiwan has more than 20 million), but it is certainly indicative of a basal level of primary productivity due to the system of agriculture which Papuans practice.
Unlike the Papuans, their Australian cousins never took up agriculture, and likely never attained the same population densities or numbers. And, they have been much more decimated by Europeans. But a question: if the people of New Guinea were isolated, why did they not suffer a major population crash? Or did they? And we simply don't know. This doesn't seem implausible on the fact of it, though a quick literature search didn't bring anything up. One issue that has be mooted is that it is clear that New Guinea had a great deal of contact with Southeast Asia over its history. Not only are the coastal people strongly influenced by Austronesians, but the western fringe of New Guinea may have been in the orbit of Majapahit, tenuous as that may be.
I am curious about New Guinea and its people, but all the accessible books or documentaries are rather similar, in sensationalizing (e.g., "headhunters!") or romanticizing (e.g., "an innocent people who know not the ways of the world"). But this enormous island is peculiar, as it resisted the wave of the Austronesians, and developed in parallel with the rest of the world its own system of agriculture. And unlike other agricultural societies there never seems to have been a phase of political consolidation. Rather, New Guinea remained pre-state, perhaps one of the most pure illustrations of Lawrence Keeley's War Before Civilization.
In any case, I'd be curious about some good book recommendations about New Guinea. I'm especially interested in the highlands.
Image credits: Wikipedia (public domain)