The evolutionary function of viruses

 Viruses have always disturbed me, theologically and even evolutionarily. They seem to be merely negative, killing purposelessly, doing nothing productive. Sure they may try to control overpopulation, but they do so so inelegantly. They are a thing on my list of "why on earth would you design things this way?" Like the sweetness of lead. 

But today I learned that in fact it may be the among the functions of viruses is the clearing of the ground for an endangered species. That's right. If humans happen to push too far into bat territory, bats will have to push out and look for new places to live. And they'll bring their viruses with them. And viruses that were never any danger to people, because people had no contact with bats, are now deadly. This secures new territory for bats. 

Suddenly viruses seem less inelegant.