This paper examines the origins of the Mortality Revolution from an evolutionary point of view, in terms of the trade-offs between virulence and disease transmission. For diseases that are transmitted person-to-person and cannot persist outside a host then there is evidence of strong selective pressure against high host lethality. However for pathogens which don’t depend on their human host for transmission or can persist outside a human host (including plague, typhus, smallpox and malaria) then the conflict between virulence and dispersal is reduced. Importantly, the properties that permitted these diseases to be so lethal also made it easier for relatively weak interventions to break the chain of disease transmission. The early control of these major diseases was associated with large reductions in mortality, but also shifted the distribution of causes of death towards the less virulent diseases of the extremes of age and of poverty.