I know it's a crazy idea, but...
Have you ever wondered about viruses, and their place within the scheme of things? I mean to say - they are not living, and they are not dead. They are intermediate between the two. They have been called "incomplete organisms"? Why? Because they are incapable of independent existence. They are simply infective DNA (or RNA)- enclosed within a protein coat. They are unable to reproduce themselves independently. The only way they can do so is by infecting a living cell - plant, animal, even bacterial - and hijacking the host's sophisticated biochemistry in order to make copies of themselves. They are parasites, in other words, and ones which have no other purpose except to make copies of themselves. They are the epitome of the "selfish gene".
It seems clear, then, that the sophisticated cell, capable of independent existence, evolved first, and the virus arrived later - as a spoiler. But why? What were the evolutionary pressures that drove the process, with such devastating consequences ( think pandemic flu, AIDS, hepatitis B, and a host of other viral diseases).
Viruses came up as a topic today on the New Scientist, and was an opportunity to fly a kite for an idea that's been incubating in this senescent brain of mine for some time.
Suppose viruses are not something radically different from, say, higher species, say pigs. Suppose they are pigs, or parts of pigs- ie a maverick version thereof - that has been spawned to keep in place those who abuse pigs.
You can probably guess what I'm driving at. At some distant point in time, man started capturing pigs, and rearing them as food. But pigs had no way of knowing their fate as pork chops on a plate. But suppose that a mutant pig developed a malady, and began sneezing. And suppose the people keeping those pigs began inhaling droplets from the air, and the pig DNA and protein in those droplets - prototype virus- invaded the mucous membranes of the farmers, weakening or killing them? That would have given the farmed pigs a way of fighting back against their "predators", and the particular trait for infecting humans, being advantageous for surviival, would have been conserved by natural selection.
You see, pigs that sneezed and infected their owners would have survived longer, with an extra window of opportunity in which to mate and pass on their mutant genes. In time, the majority of pigs would have evolved these smart viruses, ie shed-cells that can be sneezed out, that improve longevity and mating prospects. In time, other species that are kept for food, like ducks etc, would also have evolved the same trick, and ducks, pigs etc then start exchanging infective DNA and protein, giving rise to flu pandemics. It's surely no coincidence that a lot of them originate in poorer, rural communities in which farmers live in close proximity with their animals, allowing opportunity for infective material to be transmitted.
Remember - all that's necessary for a virus to be infective is for it to be able to breach the protective cell membrane of its host, and then use its DNA to start running off copies of itself within the host. The mere act of hijacking is sufficient to weaken - and sometimes kill- the host cell. But in time, the host cell develops an immune response, such that it is no longer killed outright by the virus.
So what I'm suggesting, in essence- is that viruses evolved as a form of germ warfare between one species and another. Farmed animals - pigs etc - may have been the first to strike back against us - their oppressors!