Many of us are familiar with the concept of a species at the macro (visible) scale. Dogs are dogs; pigs are pigs, and so on. Each is a distinct species based on the fact that they can only reproduce and generate fertile offspring with other members of the same species. Over the course of many generations mutations may arise in these populations which lead to different genotypes in the species. Left long enough, these two sub-populations may keep mutating to the point where they can no longer interbreed and become their own genetically distinct species. However, when you get down to the viral scale species becomes a much more difficult concept. Viruses don’t have sex in the traditional sense, so how do we determine what makes up a viral species?