Europeans Have Larger Testes than Sub-Saharan Africans but Lower Testosterone Levels

Species and subspecies differ substantially in the size of their testicles. A study has found differences in average testis size when comparing Europeans and Northeast Asians. Other studies have found differences in testosterone levels between Blacks, Whites and Northeast Asians. We sought to replicate and extend these findings in a dataset of 4,462 US soldiers (the Vietnam Experience Study). We find that those of Sub-Saharan African descent (Blacks, n = 525) average smaller testes than those of European descent (Whites, n = 3,654), d = 0.24, while Blacks average higher testosterone levels, d = 0.11. These patterns are not explained by differences in age, weight, or height. We discuss these findings in terms of evolutionary theory of sperm competition and mating systems. These differences are thought to relate to life history speed differences, especially regarding mating patterns. A more polygynous mating pattern is associated with smaller testes and high testosterone, whereas a more competitive/free mating pattern is associated with larger testes, helping with semen production and thus sperm competition. These findings are consistent with how individual level differences in ejaculate quality relate to life history speed.