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by nyssos 973 days ago
> Did evolution really keep two kidneys if you actually just need one? I doubt it.

Aside from the nervous system, pairing is the default condition of all mammalian organs which develop from the mesoderm or ectoderm: they can then go on to fuse into a single larger structure, as with the heart, but as far as I know they're never simply lost on one side during normal development.