The Double Helix

The paper Watson and Crick published in Nature on April 25, 1953 ran barely a page and its closing line was a study in calculated understatement: “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” What it had not escaped their notice was the structure that explains how life reproduces itself: two polynucleotide strands wound around each other, each strand a chain of nucleotides bearing one of four bases—adenine, thymine, guanine, cytosine—pairing specifically across the strands, A with T and G with C. The complementarity is the whole engine. Unzip the strands and each templates a new partner; heredity is base-pairing all the way down. This made genetics not merely a statistical abstraction since Mendel but a physical structure that could be drawn, and the drawing told you the mechanism. More consequentially for the present moment: it established