To ensure a biologically relevant outcome, they had to intervene—repeatedly and intelligently—in their experiment: first, by selecting only the “right-handed” versions of sugar that life requires (sugars, like amino acids, come in two mirror-image chemical structures called isomers); second, by purifying their reaction products at each step to prevent interfering cross-reactions; and third, by following a precise procedure in which they carefully selected chemically purified reagents and then choreographed the order in which those reagents were introduced into the reaction series. As my
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