The long decline of Mesoamerica

Occasionally mooted, as a club to beat the moderns, is the ninth-century drought in North America. The Turkestan suffered one of their own around that time. An earlier - worse! - one might have struck AD 100ish (ht Turtle). Thus, the trees.

Now, the human genetics. Four days back bioarXiv got a major preprint spanning all this time, from the 200s BC to the Columbian Exchange. It talks Ancient North Mesoamerica, which is Mexico to us. Yesterday le turtle set to interpret the study more fully.

Since the genomes are ancient they don't have all that Old World schmutz - and Spanish-driven internal admixture - of contemporary now-Hispanics from the region. Thus they present a capsule not only of their selves but of their ancestors.

First up is that the Spaniard came at the end of a long decline in population. The Chol-Milpa system - and the Olmec, one imagines - exploded the local population until about AD 100, when came the decline. This decline actually surprises me a bit on account the Maya and the Teohuacanos had founded some serious polities Ai.D. 200-600, far superior technologically than the Olmec. But then, Kyle Harper tells us that Rome declined too during those centuries.

The decline might have started with that Norteño drought; but between the Ai.D. 100-800 there shouldn't have been drought. There WERE some local eruptions like Ilopango and, then, the hemisphere-wide late Ai.D. 530s disaster; maybe Chichon. It could also be that civilisation worked as roach-motels, dragging people from the farm and removing them from the gene-pool. When the civilisations died, such survivors (like the Lacandon Maya) as returned to subsistence or even huntergather lifestyles could hardly maintain their prior numbers.