Something happened to Europe’s Neolithic farmers. These people had largely displaced the old hunter gatherer population in many places. Then, 5 or 6 thousand years ago they began to decline themselves. Some people have suggested they were displaced by invaders from the steppe. That has been my preferred theory. Other people think they just moved away because of stress from climate change. That would be interesting. There’s no evidence either way, or at least there’s not enough evidence to convince a majority of experts. 

Now, here we go. A new theory. Maybe it was the plague.

“Between 5,000 and 6,000 years ago, many Neolithic societies declined throughout western Eurasia due to a combination of factors that are still largely debated. Here, we report the discovery and genome reconstruction of Yersinia pestis, the etiological agent of plague, in Neolithic farmers in Sweden, pre-dating and basal to all modern and ancient known strains of this pathogen. We investigated the history of this strain by combining phylogenetic and molecular clock analyses of the bacterial genome, detailed archaeological information, and genomic analyses from infected individuals and hundreds of ancient human samples across Eurasia. These analyses revealed that multiple and independent lineages of Y. pestis branched and expanded across Eurasia during the Neolithic decline, spreading most likely through early trade networks rather than massive human migrations. Our results are consistent with the existence of a prehistoric plague pandemic that likely contributed to the decay of Neolithic populations in Europe.” (Davidski, quoting Rascovan et al., emphasis added by Davidski)

Y. pestis. Oh, very nice. This seems like good answer. It’s certainly an interesting answer.

• Davidski, “Europe’s ancient proto-cities may have been ravaged by the plague“, Eurogenes Blog (Dec. 6, 2018), reporting Rascovan et al., Emergence and Spread of Basal Lineages of Yersinia pestis during the Neolithic Decline, Cell (2019).