The great chain of being

From an article by Sean Nee in the current Nature.

Around a billion years ago, a great experiment occurred: Bacteria and Archaea came together in a fusion event to synthesize a whole new domain of life, the Eukarya. Sadly, the outcome was rather uninteresting: the resulting organisms displayed a very limited metabolic repertoire and much restricted habitat requirements.

Over the past 600 million years the Bacteria, Archaea and microbial Eukarya have continued to evolve into brand new niches. As it happens, a few branches of Eukarya — plants and animals — grew freakishly huge bodies. They also created both new substances for bacteria to exploit, such as plant lignins, and new environments for microbes to inhabit, such as feathers and urinary tracts. Indeed, some of the richest and most interesting ecologies on Earth can be found inside the animal gut.

One of the huge species, Homo sapiens, got remarkably self-important. But when, to his surprise, a virus wiped him out, most of life on Earth took no notice at all.