I don't think it is; assuming the questions of the original commentator asked can be read as a "how likely" sort of thing. I'm not saying look at the people he

I don't think it is; assuming the questions of the original commentator asked can be read as a "how likely" sort of thing. I'm not saying look at the people here and you have your answer (aside from extinction level epidemics, which we can exclude because we are here), but complex life has existed for quite a while and even humans have on a relative basis. If the sort of thing the commentator is thinking is at all likely, it very well is likely to have happened before (assuming viruses more easily evolve than more complex lifeforms do). I'm saying that we should be able to learn from what isn't here, from what didn't survive... not from what did. When we look back at what didn't make it, I don't know of many (any) cases where we say that the sudden appearance of an extremely virulent pathogen likely did in this species or that civilization. This isn't to say its impossible, but unlikely... if you perform a historical study of random individuals that play the lottery, you'll find that it's just parting a sucker from their money... yet there is nonetheless usually a winner.