Jared Diamond was right!

At least about some things. In Guns, Germs, and Steel he argued that latitudinal diffusion of agricultural toolkits was much easier than longitudinal diffusion. This seems right, but, one thing which Diamond did not emphasize enough in hindsight I suspect is that demographic diffusion and replacement can follow a similar pattern. I am probably not a "Neolithic population replacement" maximalist to the extent of someone like "Diogenes" or Peter Bellwood, but that is probably mostly a matter of my modest confidence about all of these sorts of issues. But, after running many trials of ADMIXTURE, along with perusing the results generated by Dienekes, David, and Zack, I am more confident in the position that agriculture and agriculture-bearing populations tend to initially follow paths of least ecological resistance. In kilometers the distance between Lisbon and Damascus is 4,000 units, while between Helsinki and Damascus it is 3,000 units, but Lisbon has been much more affected by the migrations from the Middle East than Helsinki. The facilitation of water transportation as well as ecological similarities between Lisbon and Damascus, at least in relation to Helsinki, explains this phenomenon. To illustrate this issue more broadly, let's look at some ADMIXTURE results. Zack Ajmal at the Harappa Ancestry Project has one of the most cosmopolitan reference sets around, and he's been posting results from his "reference 3" population, which merges a host of different study groups. Today he posted K = 6. That is, he generated 6 ancestral populations and allowed the program to assign proportions of each to individuals within the reference set. He labeled his putative ancestral populations: - S Asian - E Asian - European - SW Asian - African - American Zack generated his usual nice bar plots, but I thought there might be another way to look at the relationships between the proportions. A scatter plot where each axis represents a proportion of a putative ancestral group. Below you see "SW Asian" on the y-axis and "European" on the x-axis: