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P.S. You can see a funny analogy between HIV, its animal equivalents (FIV, SIV, dozen of others) and polymorphic computer programs. HIV/SIV/FIV mutation rate is so high that it functions on the verge of self-destruction. Therefore, this family of viruses is clearly the best sample of precious engineeging work which nature may provide. Some people would consider it as a living proof of the God existence.