Smaller Fleas to Bite ‘Em

I’ve been spending a lot of time lately talking with people about the microbiome, that cloud of bacteria, fungi, and viruses that live on all of us and (most of the time) help keep us healthy.  Much of science these days (see my post Life Inside Life Inside a Leaf) seems like a variation on the Jonathan Swift verse, from “On Poetry:  A Rhapsody.”   Swift was writing about critics, and only invoking natural history by analogy.  But he got it right:

So nat’ralists observe, a flea
Hath smaller fleas that on him prey;
And these have smaller fleas to bite ‘em.
And so proceeds Ad infinitum.