Why do we have two lungs, two kidneys instead of one bigger one but one liver, heart, pancreas? I can understand the ears and eyes' cases, to see in 3D and hear better but not in the lungs and kidneys ones I've googled but couldn't find a definite answer to this. Is it due to need for a "spare" organ upon failure? (even I don't know if you can live with one lung and the lack of a second heart) Is it because two smaller lungs/kidney work better than a single bigger one? Is there a explanation for this? Thanks!