Disease diversity and human fertility.

The existence of parasitic constraints on the evolution of life-history traits in free-living organisms has been demonstrated in several plant and animal species. However, the association between different diseases and human traits is virtually unknown. We conducted a comparative analysis on a global scale to test whether the diversity of human diseases, some of them responsible for high incidences of morbidity and mortality, were associated with host life-history characteristics. After controlling for direct confounding effects exerted by historical, spatial, economic, and population patterns and their interactions, our findings show that human fertility increases with the diversity and structure of disease types. Thus, disease control may not only lower the costs associated with morbidity, but could also contribute directly or indirectly to reductions in human population growth.