Infectious disease and group size: More than just a numbers game

Charles L. Nunn, Ferenc Jordan, Collin M. Mc-Cabe, Jennifer L. Verdolin, Jennifer Fewell

Research output: Contribution to journalArticlepeer-review

112 Scopus citations


Increased risk of infectious disease is assumed to be a major cost of group living, yet empirical evidence for this effect is mixed. We studied whether larger social groups are more subdivided structurally. If so, the social subdivisions that form in larger groups may act as barriers to the spread of infection, weakening the association between group size and infectious disease. To investigate this ‘social bottleneck’ hypothesis, we examined the association between group size and four network structure metrics in 43 vertebrate and invertebrate species. We focused on metrics involving modularity, clustering, distance and centralization. In a meta-analysis of intraspecific variation in social networks, modularity showed positive associations with network size, with a weaker but still positive effect in cross-species analyses. Network distance also showed a positive association with group size when using intraspecific variation. We then used a theoretical model to explore the effects of subgrouping relative to other effects that influence disease spread in socially structured populations. Outbreaks reached higher prevalence when groups were larger, but subgrouping reduced prevalence. Subgrouping also acted as a ‘brake’ on disease spread between groups.We suggest research directions to understand the conditions under which larger groups become more subdivided, and to devise new metrics that account for subgrouping when investigating the links between sociality and infectious disease risk.

Original languageEnglish (US)
JournalPhilosophical Transactions of the Royal Society B: Biological Sciences
Issue number1669
StatePublished - May 26 2015


  • Comparative analysis
  • Infectious disease
  • Meta-analysis
  • Social network
  • Social structure
  • Sociality

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)


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