Fig. 2.

Selection need not maximize the duration of infection. Two hypothetical strains differ in their transmission rates over the course of infection, and selection would be expected to maximize the lifetime transmission success. In panel A, both strains maintain identical transmission rates through time, except that Strain 2 can maintain infection (and transmission) longer and would hence be favoured by selection. In contrast, panel B assumes that shorter infections allow substantially higher rates of transmission. Strain 2 has the greatest cumulative transmission success, despite causing a shorter infection (e.g. by killing the host more quickly), and should thus be favoured over Strain 1.