Immunity to colds etc.

I think the same, Mishap. When the world comes to an end because of what man has done to it, all that will be left will be viruses and insects.
Viruses are clever because they mutate every few generations.
People quite often misunderstand the word fit. It means most suitable, not strongest.

rosequartz well yes hay fever is an over reaction of the immune system to an outside stimulus - pollen. Its an allergy. Sometimes people grow out of allergies. But it is a whole different division of the immune system to the bit that deals with viruses. Bit like the navy has different methods to the army, although they are both part of a country's defence system.

Thanks JessM.