where C IS (t) denotes the contact per susceptible neighbour and ψ(t) denotes the infectiousness at time t after infection. Kao [21] showed that novel pathogens may evolve towards a lower R 0 , even if this results in pathogen extinction. This is because the presence of exploitable heterogeneities, such as high variance in the number of potentially infectious contacts, increases R 0 ; thus, pathogens that can exploit heterogeneities in the contact structure have an advantage over those that do not. The exploitation of heterogeneities results in a more rapid depletion of the potentially susceptible neighbourhood for an infected host. While the low R 0 strategy is never evolutionarily stable, invading strains with higher R 0 will also converge to the low R 0 strategy if not sufficiently different from the resident strain. This is in contrast to the conventional belief that the emergence of novel pathogens is driven by maximisation of R 0 .