It’s a remarkable coincidence that the X and Y chromosomes, named that way because those are the only letters that describe their shapes, sit together in man’s cells, defining their maleness, just as they sit next to each other in the alphabet, and that those two letters are also the ones we think of first when having to assign variable names or label the axes of a scatterplot. They are next to each other in the world of letters, in math, and in us. It’s a remarkable coincidence, but not a significant one.