Interesting paper, Climate shaped how Neolithic farmers and European hunter-gatherers interacted after a major slowdown from 6,100 BCE to 4,500 BCE:

The Neolithic transition in Europe was driven by the rapid dispersal of Near Eastern farmers who, over a period of 3,500 years, brought food production to the furthest corners of the continent. However, this wave of expansion was far from homogeneous, and climatic factors may have driven a marked slowdown observed at higher latitudes. Here, we test this hypothesis by assembling a large database of archaeological dates of first arrival of farming to quantify the expansion dynamics. We identify four axes of expansion and observe a slowdown along three axes when crossing the same climatic threshold. This threshold reflects the quality of the growing season, suggesting that Near Eastern crops might have struggled under more challenging climatic conditions. This same threshold also predicts the mixing of farmers and hunter-gatherers as estimated from ancient DNA, suggesting that unreliable yields in these regions might have favoured the contact between the two groups.

This is not a surprising result. I predicted this (along with many others) pattern in the late 2000s. It was just not plausible that a ‘spherical cow’ diffusion process characterized the expansion of farming. There is real topography and climate to deal with.

Jared Diamond’s Guns, Germs, and Steel comes in for a lot of criticism, but the insight of latitudinal migration being easier than longitudinal has been pretty spot-on. These authors find Neolithic expansion across the Mediterranean much faster and easier to model than that going north. Pretty clearly the Near Eastern farming cultural package was a poor fit to Northern Europe, and it took some adaptation for it to get good.

That being said, I think another aspect which is going to be impossible to model in a specific sense, is that there were political and social reasons for how and when these Neolithic lifestyles spread. To give a strange analogy, the massive internal war in the Arab Empire in the late 7th century gave Byzantium a major respite from external pressure and allowed it to recover. It’s totally plausible that chaos in a Neolithic tribal confederacy might give hunter-gatherer clans time to recover and retaliate.

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.