??? ive only got one eye - other had to be removed due to "medical problems" whatever that is...but i can recognise and realise depth, and perceive it absolutley fine! ive been blind out of it since i was 2, and had it removed when i was 19. never had any problems. my good eye is just that. no problem with it at all. so, i can conclude, one eye is sufficant enough to survive, cuz i do just fine!
I guess hearts are just too big and important to double up on, Whickerman. So a car might have a spare tyre and even some tools but it's not going to include a second engine. But people get by on one eye, one ear, one kidney (and even, with some help, one leg).
i wonder though, how would two hearts in a human actually work? where would it fit for a start, second, would it beat the same? would we live longer? or would we live the about the same, only with a chance of been healthier, as weve got two hearts. what would happen if we have a heart attack? would it matter? if one hearts fine, the other crap? hehe! just wondering, maybe that question should be on another thred!
if you mean purely to survive, there are loads - eyelashes, eyebrows, all body hair, teeth, eyes, ribs, nose, nipples, boobs, legs, knees, ears, lips, etc etc etc, - these things would cause hardships and make you more vulnerable, but you would be able to actually be alive.
there are people with no arms or legs, who can't hear, see, taste, smell, have no bowels, or bladder etc etc and survive ok.