Biology: A Tree of Eukaryotes

Catharina Coenen


Listen to A Tree of the Eukaryotes:


I spend my days teaching about strangers: blobs of slime, walkers on legs that aren’t legs, seers with eyes that aren’t eyes. Most days I walk through biology in the dark, my hands outstretched, calling to those who walk behind me, holding on to the hem of my shirt: “Watch out, there’s a bump here,” “give me your hand: feel how smooth this is,” “taste this,” “now: duck.”


Teaching equals storytelling about shadows on the wall; the slide projector, my bonfire in Plato’s cave. Most days it feels like singing in the dark.


The tree of the eukaryotes was like that. For decades, I taught about forks in the road of evolution of the nucleated cells: left to the fungi, right to the animals. Remember, we lost the plants way back, one point five billion years ago, though by then we had stuck it out together, through hell and high water, for a half a billion years. And, oh yes, finally, don’t forget to look over there, far off to the left: see that big bag full of beings we don’t know what to do with? The amoebae, protozoans, flagellates? The algae, water molds, and parameciums? We call them protists. And then we usually just leave them there, rattling around together, like the scissors, string, and thumbtacks; the postcard from Aunt Mary we never got around to answering; the wine bottle corks we always meant to make into something else, the potholders and the shipping tape. That most important drawer in our kitchen where we keep things joined only by our inability to figure out where they belong.


But then: someone cared enough!  Many people did. For decades, they deep-read the DNA. They scratched their heads. They sorted. They debated. They tried again. And then they said: “This isn’t quite right, and yes, we’re going to mess with this some more, and probably we’ll keep on messing for many years to come. We never may be done. But meanwhile: here’s a map.”


A map of sorts. Not like the maps of yore, with large white swaths—here be dragons—but one with way too many names and lines. Like barcodes bristling out in all directions, forming a frightened porcupine. Like the world’s most complicated game of pick-up sticks. The tree, the river delta, the forks in the road, had burst into a sun, a wild wheel, orange, yellow, red. A solar explosion, with many roads erupting from the center all at once.


Well, you know, we just don’t know. Right here, at the heart of things? Is mystery. Yes, we know there ought to be a single root, but for right now, life’s not a tree and not a bush—it is a tumbleweed.


Thank you, I sighed. For being honest. Thank you for the fierce orange glow.


The slime molds had come home, snuggling up against fungi and animals, asking “will you be my neighbor?” The amoebae, like splattered raw egg white, had fragmented all over everything, crawling along branches far apart. Adoption of chloroplasts by nucleated cells happened not once, but here, and here, and here, leaving hope for the future. (Really, you have never wanted to be green?)


“But, in the end, the point is,” I tell my students, waving my hands, “the point is that, right now, some of the cells that are your blood hunt, blob-like, for bacteria like amoebae crawling through a bog. Along your airways your ciliated cells beat in unison, like a blanket woven from a thousand docile parameciums. Bone precipitates in tiny spaces made by cells pretending to be foraminifers. And they all talk, sing symphonies of molecules, hum melodies of chemistry they picked up in archaeal soup: We’re in this together, sharing wild inventions. Your body came from a flagellate swimming towards an egg’s scent with the same whiplash strokes used by any microscopic alga making a red tide.”


I still lie to my students, all the way through years one and two. I still teach them to count: one—animals, two—fungi, three—plants, four—protists, five—bacteria. A lie of separation, as blatant as it is safe; a rooted story branching towards a familiar present tense. I lull them, so they’ll follow me into the dark. And then I let them hate me when the sun bursts out: I yank the root and watch them flail, initiate them into the tribe of tumbleweeds.


Provenance: Submission

Catharina Coenen is a plant biologist and first-generation German immigrant to Northwestern Pennsylvania, where she teaches biology at Allegheny College. Her academic research has been published in Plant PhysiologyNew Phytologist and other plant biology journals. Her creative nonfiction pieces are forthcoming in Appalachian Heritage, Christian Science Monitor, and elsewhere.



Featured Image: “Fucus” by JJ is licensed under CC BY 2.0

Author Photo by River Branch


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