“How singular is the thing called pleasure, and how curiously related to pain, which might be thought to be the opposite of it…he who pursues either of them is generally compelled to take the other. They are two, and yet they grow together out of one head or stem.” This philosophical observation, recorded around 350 B.C.E., astutely predicted the experimental insights of the nineteenth-century French physiologist Claude Bernard. Bernard is credited as the first to note that moving between opposite biological states enables our bodies to maintain stability in the face of disruption—anything
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