This research uses evolutionary theory to evaluate followers' preferences for physically formidable leaders and to identify conditions that stimulate those preferences. It employs a population-based survey experiment (N ≥ 760), which offers the advantages to internal validity of experiments and external validity of a highly heterogeneous sample drawn from a nationally representative subject pool. The theoretical argument proffered here is followers tend to prefer leaders with greater physical formidability because of evolutionary adaptations derived from humans' violent ancestral environment. In this environment, individuals who allied with and ultimately followed physically powerful partners were more likely to acquire and retain important resources necessary for survival and reproduction because the presence of the physically powerful partner cued opponents to avoid a challenge for the resources or risk a costly confrontation. This argument suggests and the results indicate that threatening (war) and nonthreatening (peace, cooperation, and control) stimuli differentially motivate preferences for physically formidable leaders. In particular, the findings suggest threatening conditions lead to preferences for leaders with more powerful physical attributes, both anthropometric (i.e., weight, height, and body mass index) and perceptual (i.e., attributes of being “physically imposing or intimidating” and “physically strong”). Overall, this research offers a theoretical framework from which to understand this otherwise seemingly irrational phenomenon. Further, it advances the emerging but long-neglected investigation of biological effects on political behavior and has implications for a fundamental process in democratic society, leader selection.