The Weird Event That Led to You and Ewe and Yew

Life arose on earth over three billion years ago, and for a long time, there were only one-celled organisms. These prokaryotes diverged and evolved in many ways, but making the leap from one cell to many cells (eukaryotes) was a paradigm shift that led to every living thing on earth that’s big enough for us to see -including us. How did that happen? Before we could sequence genes, the prevailing theory was a gradual development as cells mutated, diverged, and evolved. However, recent genetic research has led credence to the idea that the first two-celled organism was a merger that only happened once.

The alternative—let’s call it the “sudden-origin” camp—is very different. It dispenses with slow, Darwinian progress and says that eukaryotes were born through the abrupt and dramatic union of two prokaryotes. One was a bacterium. The other was part of the other great lineage of prokaryotes: the archaea. (More about them later.) These two microbes look superficially alike, but they are as different in their biochemistry as PCs…