nature taking it's course is one thing, and i don't think that's the thing we're all talking about here. of course it's impossible to live without causing some... death? i don't know the right word. but that doesn't mean that it's ok to cage animals and experiment on them.
and no, i don't really think human life is more "important" than any other. maybe we should try to define "important," as i do not think that in the grand scheme of things, human life carries any more value than any other life.
i didn't pose the question. i'm simply trying to respond to it in a way that gets my point across the questioner.