When Two is Too Many and Not Enough: Discoveries on the Stability of Shared Leadership from Rome to Mars

Leadership research has established the benefits of shared leadership, but much less is known about its stability. Drawing on data from NASA space analog teams and Ancient Rome (32 BCE–491 CE), we discover that the number of leaders critically shapes whether shared leadership persists or changes form. Using observational data from 13 NASA crews and historiometric data from the Roman Empire, we find that shared leadership often arises in both contexts, but its stability varies markedly. Specifically, while both hierarchical leadership (single leader) and group shared leadership (three or more leaders) tend to persist, dyadic shared leadership (two leaders) is uniquely unstable. This