Prior research finds that sex ratio, defined as the proportion of males and females in a given context, is related to engagement
in risk-taking behaviors. However, most research operationalizes sex ratio at a local context (e.g., regional or county), which
fails to reflect with precision the sex ratios contexts of individuals at a closer level. Furthermore, the relationship between sex
ratio and risk-taking behaviors may be affected by individuals’ life history strategy, with previous studies showing fast life
history strategies linked to risk-taking behaviors, compared to slow life history strategies. The present study analyzes the
relationship between classroom sex ratio and risk-taking behaviors and the interaction between classroom sex ratio and life
history strategy in adolescents. The sample comprised 1214 participants nested in 57 classrooms, 49.75% females, 91.5%
Spanish and a mean age of 16.15 years (SD = 1.23, range 14–21). Results from multilevel modeling showed a negative
relation between classroom sex ratio and risk-taking behaviors in female adolescents with faster life history strategy. By
contrast, classroom sex ratio in male adolescents related positively to risk-taking behaviors but did not interact with life
history strategy. These findings underscore the importance of studying proximate sex ratio on risk-taking behaviors in
adolescents and underline its potential influence in the development and expression of life history strategies
