Epilogue: Challenges for the future

Charles Darwin contemplated the evolution of diversity within species in his book, On the Origin of Species. Darwin noted that there are profound differences between the sexes of a single species that evolve through a process he termed sexual selection. We propose that consideration of the adaptive significance as well as the mechanisms underlying why males and females respond differently to infection is fundamental for progress in infectious disease research. Future studies must consider not only the role that hormones play in modulating responses to infection, but also how genes, including sex chromosomal genes, impact responses to infection differentially between the sexes. Finally, by illustrating that sex and reproductive status impact responses to infection it is demonstrated that these factors might also influence responses to therapeutic treatments, including vaccines.