Social Group Maxima: The Breaking Point

Open Access
Greenleaf, Didier David
Area of Honors:
Chemical Engineering
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Darrell Velegol, Thesis Supervisor
  • Themis Matsoukas, Honors Advisor
  • Sociology
  • Group Dynamics
  • Robin Dunbar
  • Dunbar's Number
What if you were told that your brain would not allow you to have strong relationships with more than 150 people? According to Robin Dunbar, that statement might not be too far off. Dunbar found in a study of primates in their natural environment that the neocortex size (a portion of the brain known as the critical thinking section) correlated well verses mean group size. When this relationship was extrapolated for humans, he found a mean group size of 150. However, how can groups for humans be measured? With conventional definitions containing vague, immeasurable terms, a more usable definition was derived: “A number of individuals that recognize the names of, have had conversations within the past three months, and share a common goal with one another” With this definition, a survey study was done on the spring 2010 graduating Chemical Engineers of Penn State University. It was found with 95% certainty that the true mean group size was 15.8 ± 5.1. This number was much less than Dunbar’s quoted number of 150, but it should be noted that his number is a social limit of a human, rather than the size of one single group found in this study. However, what occurs after the number of 150? In order to test this, a mathematical model was used to simulate the growth of bacteria in a multiple substrate environment. It was hypothesized that when growth parameters were allowed to mutate over time, distinct species would arise. Bacteria growing to a critical population causing speciation would mimic the ‘splintering’ or breaking of groups after going over the maximum. Running the simulation twice with 10,000 generations showed results that supported our hypothesis, however more testing needs to be done for confirmation.