Over generations, this selection pressure can shift the frequency of immune-related genetic variants in a population — increasing the frequency of variants that were associated with survival and decreasing the frequency of variants that were not.

If the post-contact epidemics exerted this kind of selective pressure on the Maya population, we might expect to see differences in the frequencies of specific immune-related genetic variants between the pre-contact ancient individuals (who were never exposed to European diseases) and the modern individuals (whose ancestors survived the epidemic period).

The 2024 study investigated this prediction and found evidence consistent with it: certain immune-related genetic variants showed patterns of frequency change between the ancient and modern samples that are consistent with selection during the epidemic period.

This finding adds a biological dimension to the historical record of the catastrophic post-contact epidemics.