Professionalism Cat pictures Pick one . s <| sep |> So , an out the ass evolutionary perspective might be that whatever causes your apocalyptic hellscape caused a huge amount of mutation to occur . In the next generation , most offspring are stillborn , those that aren ' t are badly ballsed up . You end up with only mutants being able to mate with mutants because mutants aren ' t going to be preferentially mated with by healthy animals and the drastically reduced populations result in a founder ' s effect sortof occurrence . Fairly rapidly for macro evolution the surviving , ballsed up creatures diversify to fill new niches which is facilitated by the new suite of mutations they have to be selected on . Over time more damaging mutations are selected out , organisms live longer , are more fit . Eventually you end up with a pretty alien environment . Anyway , that really wouldn ' t work , but it sounds plausible enough that I don ' t think most people would question it if you say it fast and don ' t mention it again .