One of the great triumphs of twentieth-century biology was the discovery of how genes make proteins. Genes are encoded in DNA. To turn the sequence of a gene into a protein, a number of molecules gather around it. Reading its sequence, they produce a single-stranded version of it made of RNA, called a transcript. The transcript gets shipped to a cluster of other molecules, the ribosome, which picks out building blocks to construct a protein that corresponds to the gene. The protein floats off to do its job, whether that job is to catch light, digest food, or help generate a thought.

We have about 20,000 protein-coding genes. If you tally up the amount of DNA they constitute, you get less