The authors test the relationship between linguistic diversity and parasite richness, theorizing that anti-pathogen behaviors, such as the favoring of contact with a limited range of similar, nearby populations carrying the same suite of parasites and pathogens, will be selected for due to variability in immunobiological makeup between groups. As a result, cultural and gene pool isolation will be likely to further divide local parasite-host groups, generating language diversity as well as population divergence and new evolutionary forms among the parasites themselves. A significant positive correlation is found, which the authors suggest has important implications for future research regarding cross-cultural transmission and interaction.