Learning by Subtraction: How Human Biology Reveals What We Can Live Without
Medicine cannot remove human functions simply to discover which ones matter. Nature, disease and accident nevertheless produce cases that resemble experiments in subtraction. Some people carry damaging variants in both copies of a gene. Others develop without an organ, lose one through disease or surgery, or survive injuries that remove substantial parts of the body. Modern medicine creates another category by transferring biological work to drugs, prostheses and machines. These cases offer an empirical route into the question of what a human system actually requires. But survival is an ambiguous result. A person who lives without a structure has not necessarily shown that it was useless. Another pathway may have absorbed its work, development may have reorganised around its absence, or medicine may be supplying enough of the missing function to keep the larger system operating. The cost may also remain hidden until infection, injury, pregnancy, ageing or some other form of stres...