Population structure and excess mortality among young men in the United States.

In this study I examine local variation in the timing and magnitude of the excess mortality hump, which is the period in adolescence and in young adulthood when mortality rates spike in young men due to an increase in risk-taking behaviors believed to result from a surge of testosterone production and subsequent aggressive, impulsive behaviors. Using an ecological framework and data on all-cause mortality in the United States between 2000 and 2018, I test the hypothesis that dimensions of the local population structure will exacerbate testosterone production and intraspecific competition among young men, which in turn leads to behaviors that elevate the risk of death. This hypothesis is supported by the data. I find that the age at the peak of the excess mortality hump is younger in counties where the sex ratio skews toward males and where population density is high. Additionally, I find that the overall magnitude of the peak of the excess mortality hump is greater in counties where the sex ratio skews toward males.