I recently recorded a podcast with Anders Bergstrom discussing his paper from a few years back, A Neolithic expansion, but strong genetic structure, in the independent history of New Guinea. This got me to thinking a bit about the patterns over the last ~5,000 years within the island, and more broadly. The island of New Guinea is about the size of Texas. That means it’s a bit larger than France. Much of the population is concentrated regionally in the highlands, where a productive system of gardening agriculture dates back 7,000 years.
One of the main results from Anders’ paper is that though New Guinea seems to undergone demographic expansion with the rise of agriculture, there is no evidence of star-phylogenies on the Y chromosome that you see elsewhere in the world, and genetic distances between populations seem to be rather high at a local scale. You’ll have to listen to the podcast (I think it will probably go live in August, so just subscribe) to get the precise way Anders said this, but one thing I got from the conversation is that the cultural and genetic diversity of the highlands is a function of evolution after a Neolithic expansion of a more homogeneous population. That is, I had assumed that the “Papuan” language family was an artificial construct where a bunch of different unrelated dialects was thrown together, but it seems perhaps they have a common genetic origin in an ancestral population that took up taro farming.
This has huge implications for the rate of linguistic evolution of human societies. Like genetic diversity linguistic diversity emerges in the context of cultural parameters. For example, without literacy and widespread trade, one can imagine oral dialects diverging rapidly. Similarly, without gene flow between neighboring populations, they can rapidly differentiate with small effective populations.
One thing I wonder about is how similar this was the spread of swidden agriculture in Europe. Where the Cardial and LBK cultures originally homogeneous, but eventually fractured into small paramountcies? And why and how did the steppe-derived populations roll over these populations so quickly, and give rise to the ‘star-phylogeny’ Y chromosomes we see today?
Bergstrom makes some general allusion to the emergence of metal. But at this point, geneticists usually pass the buck to prehistorians, archaeologists, and economists. What about the rise of metals resulted in the explosion of paternal lineages, and cranked up gene flow between neighboring populations?
The easy way to explain this is that spears and swords of metal impose the rule of the few upon the many. But I think we need to consider the economic consequence of widespread metal (especially iron) in agriculture, where clearing virgin and the second-growth forest became much easier for peasants, and the social and manufacturing systems needed to produce metal weapons and tools at scale. Combined with the mobility of the horse, the shift into the Bronze and Iron Age across Eurasia resulted in the rise of an almost totalitarian and globalist social order in comparison to the localized and decentralized village societies of the Neolithic.