The demographic devastation was so severe, and the selective pressure so intense, that it left a detectable genetic signature in the immune systems of the surviving population’s descendants.

The modern Maya people of Tixcacaltuyub carry, in their immune gene frequencies, the trace of what their ancestors survived in the sixteenth and seventeenth centuries.

This genomic evidence does not tell us anything that historical sources did not already establish about the severity of the post-contact epidemics.

But it provides independent, biological corroboration of that history, and it adds specificity about which aspects of the immune system were most affected by the selective pressure of specific diseases.

For the people whose history is being investigated, this finding is not abstract.