viruses, we'd like to talk about them having a unitarian genomic sequence by thibodeau. it's a whole population with a bell curve and you're just sampling right down the middle. but within that huge population, there's a fitness for all sorts of different if i ventured so if it moves him here to there, and this requires a slightly different property, then those genomes that are present within a population will begin to set a new set point describes the middle. so you're going to think about the viruses as a whole swarm of what we call quasi-species. and viruses as they reproduce their nuclei acid, every time they make, say a thousand, that one error, so .1% error rate. and if you multiply that over minutes and hours, there's a lot of opportunity for different fitness environments. and in addition, flu viruses as captain dan was saying, have the ability out on to mutate in that way, but also they can exchange genome segments. if you've got an animal infected with two different flu viruses, it can swap out genome segments, and very rapidly develop a whole new landscape. an