Every time one of the cells in your body divides, it has to double its quota of DNA so that each daughter cell gets a complete set. DNA is a replicator—a molecule that can be accurately duplicated, admittedly with some help from proteins. DNA has been doing this for billions of years, well before there were humans, before animals existed, and probably before the first cells evolved.

But what came before DNA? Probably RNA, a related molecule. Certain types of RNA can store genetic information, just like DNA. And much like proteins, they can fold into three-dimensional shapes to speed up chemical reactions, among other functions—these are called ribozymes.

The dominant theory is that an “RNA world” preceded the origin of