Yeah, the point I'm making is not that all mutations are special and natural, which isn't particularly useful: it's that we almost certainly have mutations simi

Yeah, the point I'm making is not that all mutations are special and natural, which isn't particularly useful: it's that we almost certainly have mutations similar to those that cause Down syndrome in our genetic history, and ancestors who suffered comparable (although presumably different) disadvantages relative to baseline mammals/apes/humans of the day.