A highly-virulent pathogen is reproducing in the host most quickly, so it should "win," and therefore most pathogens should evolve to be highly virulent. Why don't they?
A. Pathogens don't evolve like other living things.
B. A highly virulent pathogen may be less likely to infect more humans if it disables the first host too quickly.
C. Some pathogens can't reproduce that fast so they never get to the point where they kill the host.
D. Natural selection wouldn't select for "deadliness."
E. Most pathogens are highly virulent.