We document the historical roots and contemporary consequences of masculinity norms—beliefs about the proper conduct of men. We exploit a natural experiment in which convict transportation in the $$18^{\textrm{th}}$$
18
th
and $$19^{\textrm{th}}$$
19
th
centuries created a variegated spatial pattern of sex ratios across Australia. We show that in areas with heavily male-biased convict populations, relatively more men volunteered for World War I about a century later. Even at present these areas remain characterized by more violence, higher rates of male suicide and other forms of preventable male mortality, and more male-stereotypical occupational segregation. Moreover, in these historically male-biased areas, more Australians recently voted against same-sex marriage and boys—but not girls—are more likely to be bullied in school. We interpret these results as manifestations of masculinity norms that emerged due to intense local male-male competition. Once established, masculinity norms persisted over time through family socialization as well as peer socialization in schools.