Nov 222013

Stewart Brand usually gets credit for the quote, but apparently it was Craig Venter who said it: “If you don’t like bacteria, you’re on the wrong planet.  This is the planet of the bacteria.”

Actually, the second part of that, the play on Planet of the Apes, was probably lifted from the title of an article by Stephen Jay Gould, included in his book Full House.  When I was asked to review the book, eighteen years ago, one passage blew a hole in my world view: “We live now in the ‘Age of Bacteria.’ Our planet has always been in the ‘Age of Bacteria,’ ever since the first fossils—bacteria, of course—were entombed in rocks more than 3 billion years ago.”

It’s funny that it was Stephen Jay Gould who steered me away from my zoocentricity, because the preeminent explainer of evolutionary biology rarely had much to say about microbes. Pulling one of his books off the shelf and scanning for organism names in the index, I see: ammonites, aphid, angler fish, Archaopteryx, asses, Australopithecus–ah, there’s “bacteria,” with two brief entries–and then, bees, birds, Blatella germanica (a cockroach), blue-footed boobies, boobies again, then brown boobies, brown hyenas, coelecanths….and so it continues until we get to Eschirichia coli, and much later, two entries for “prokaryotes.”  That’s it for microbiology in that book (Hen’s Teeth and Horse’s Toes).

Protists don’t rate a single mention. And it is much the same story in Gould’s other works.  Even his desk-bending opus ultimum, The Structure of Evolutionary Theory, mentions “protistans” just a handful of times, mostly in connection with the observation that gradualism will govern the rate of evolutionary change in “asexual” organisms.  (Most protists are as sexy as can be, but let’s leave that aside, for now).

I didn’t bring this up to bash Gould.  He wrote mainly for a general readership, and microbiology wasn’t his thing anyway. But perhaps it reveals something that, as late as 2002,  it was possible to write a 1,400 page treatise on evolutionary theory in which the only source cited on “protistans” is D’Arcy Thompson’s On Growth and Form, published in 1917. And I’m not sure that Gould’s zoocentrism is all that unusual in his field.  Certainly, Lynn Margulis (enthusiastically wrong about some things, but the best friend a microbe ever had) often complained loudly about the dominance of “zoologists who today call themselves ‘evolutionary biologists’.” (Acquiring Genomes, 26) Last year, there was an international congress on evolutionary biology in the big city down the road from my village. Scanning the program, I noticed that most of the talks were centred around macroorganisms of one kind or another (tigers, termites, toadstools, and tumtum trees). A friend who teaches evolutionary biology at CUNY was in town for the event. “Don’t worry,” he teased me, “there’s bound to be one or two people giving talks about the weird stuff!”

As my friend knows quite well, here on the “Planet of the Bacteria,” the “weird stuff” is really creatures like us: great, shambling, genetically-coordinated quasi-colonies, lurching around with more than 37 trillion specialized cells inside them (and hosting perhaps ten times that number of hitchhiker microbes).   The protists seem almost normal, by comparison, though even they are evolutionary oddballs.  All of us eukaryotes are weird, but, some of us are weirder than others.  While plants, fungi and animals make up only a few remote twigs at one end of the eukaryote lineage, the long sideways-projecting stalk on which they sit– comprising what is sometimes called (though I can hardly say it without snickering) “Empire Eukaryota”– is made up mainly of (royal fanfare, please) “Kingdom Protista.”

Needless to say, the natural history of eukaryota was mostly written by protists, and by all rights the study of them ought to be central to evolutionary theory.   Bear in mind that if the original ancestral eukaryote were to emerge from some magic time capsule and land in the petri dish of a modern biologist, it would almost certainly be classified as a protist.   And, if you look closely enough at some of our 37 trillion cells, our kinship with them is hard to miss.  Our lungs and fallopian tubes have genuine cilia that beat just like those of the ciliated protozoa.  Our sperm have flagella (really just another kind of cilium), no different, structurally, from those that power any flagellated protist.  Our bodily fluids are patrolled by ravenous amoeboids that roam around, engulfing bacteria and other other invaders.    Out here in the “Empire” of nucleated cells, protists are us.


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