Question
Why didn’t natural selection lead to the evolution of such totally harmless parasites?
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Answer
Being a parasite means causing trouble or harm to the host. When host-parasite relationship is concerned both of them evolve together which is also called co¬evolution. If totally harmless parasite has to be evolved through natural selection, then such parasite will not remain as a parasite but will become commensal or can show amensalism. Therefore, natural selection does not lead to evolution of totally harmless parasite.
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