the symbion is going to become extinct echoes that earn down its own house but if you can have a big family and say it's time to leave the house and find another one and then burned down it's okay. so actually these viruses and other pathogens use all the different levels of deadliness and sometimes you can see this in the wild. for example some fool decided it would give good idea to introduce rabbits to australia and it tookd off and they said how do we control them? there's a horribly deadly virus that kills pearce in europe and they said will bring it to australia problem solved. it started killing them offa le crazy and then it started to become more deadly and is still not a good idea for rabbits to get sick with a virus. the virus evolved and essentially adjusted to the deadliness to be able to get the host and thehe most efficient wy for making more viruses. and it's hard for us because we think about things ashi being gd in bedei is very sort of an egocentric way that these things are not just evolving over the course of a few years. they are evolving over millions of years