While Darwin's picture of biological evolution was incredibly important
in the history of scientific thought, some systems seem to
elude it's elegant explanations. Here's a picture of the evolution
of disease virulence (defined in terms of transmission rate and
infection duration) for a variation of Bailey's lattice model.
The curves represent the average population phenotype, and the color
changes from black to yellow as time progresses.
have observered that evolution seems to minimize infection
duration while maximizing transmission rate. With a slight increase
in mutation rate, though, we also can recover the Darwinian
expectation of maximizing both transmission and duration.
So, intuition still holds, but spatial population
structure can introduce non-obvious complications into disease