Coupled Contagion

Paul Smaldino and I have a new paper out in Evolutionary Human Sciences. We show that in a polarized population the joint dynamics of cultural adoption and disease transmission can quickly become very complex. We focus on two social processes, homophily and out-group aversion. People preferentially interact with others like themselves and they avoid adopting the behavior of people who are not like them.

One of the most interesting patterns we observed was when both homophily and out-group aversion are high and people can learn protective behaviors (e.g., masking, social distancing), epidemics that start in one group quickly die out but are picked up by the other group and end up being much worse -- i.e., infect a greater proportion of that segment of the population. This pattern is reminiscent of the observed dynamics in the US during the SARS-CoV-2 pandemic.

We actually wrote this paper in April-May 2020. Publication was delayed because it languished at PNAS for nearly 100 days before receiving a negative review. Fortunately, we were able to get the ideas out in a preprint. EHS was much faster and more professional -- I highly recommend the journal.