The Minimal Human: How Much of the Body Does a Mind Need?
A human being can lose an arm without losing any obvious part of their consciousness. The same is true of a leg, a kidney or one lung. Machines can also assume selected functions once treated as inseparable from particular organs: a total artificial heart can replace damaged ventricles and valves, extracorporeal support can temporarily provide circulation and gas exchange, and dialysis can remove waste and excess fluid from the blood. Taken far enough, these substitutions invite a disquieting question: how much of the body could disappear before the remaining system stopped being a person? The obvious answer is that the brain must remain. So long as the brain survives, we may be tempted to regard everything else as support equipment—biologically indispensable in ordinary life, but not itself the seat of consciousness. Yet a brain does not simply require oxygen and glucose. It develops and operates within continuous exchange with circulation, respiration, metabolism, hormones, immu...