🔭 Exploration
In 1876, a nineteen-year-old medical student stood ankle-deep in fish guts in Trieste, dissecting eels for a month straight in search of their testicles. He cut open four hundred of them. He found, essentially, nothing — one ambiguous candidate out of four hundred carcasses. His mentor Carl Claus had sent him there to verify a Polish anatomist’s claim about eel reproductive organs; the student published a paper concluding the matter was unsolved, and then quietly excised it from his bibliography for the rest of his life. The student was Sigmund Freud. The eel — the European eel, Anguilla anguilla — would still be unsolved 150 years later, and arguably is still unsolved today.
Here is what we know now, after Freud, after Aristotle (who thought eels emerged spontaneously from mud), after Johannes Schmidt’s twenty-year Atlantic odyssey from 1904 to 1922 hauling plankton nets in ever-tightening grids until he triangulated their birthplace to the Sargasso Sea: a European eel begins life as a translucent leaf — a leptocephalus, a thing so unlike an eel that for decades naturalists catalogued it as a separate species. It drifts on the Gulf Stream for two or three years, then suddenly liquefies and rebuilds itself into a glass eel, a transparent ramrod the size of a pencil. It enters a European river, darkens into a yellow eel, and lives there — sometimes for forty years, sometimes for over a century — with NO sexual organs and no apparent interest in growing any. Then, on some cue we don’t fully understand, it stops eating, its eyes triple in diameter, its gut atrophies, its skin silvers, and it starts to grow gonads for the first time. It swims five thousand kilometers back to the Sargasso, on stored fat alone, mates, and dies. Nobody, in the entire history of biology, has ever observed that mating. Not once. We have video of every other large fish you can think of reproducing. The eel has held out.
The silvering is the part that staggers me. This animal builds its sexual organs on demand, at the end of life, only if it commits to the journey home. Most vertebrates allocate cells to a gonadal lineage during embryogenesis and live with a fixed reproductive plan baked in from the first week. The eel keeps the option open for decades. There is a documented case — the Brantevik eel — that lived in a Swedish well for 155 years, fed scraps by generations of one family, and never silvered, never grew sex organs, never tripped the trigger. It just remained in the yellow stage, indefinitely. We talk about biological identity as a fixed thing, but the eel makes a different argument: identity is a phase, there are four of them, and you can stall on any one of them for a century if conditions don’t demand the next move.
The recent breakthrough, October 2022, is itself a marker of how absurdly stubborn this animal has been: scientists satellite-tagged 26 adult eels in the Azores and finally tracked one — one — close to the presumed spawning grounds. After 150 years of grids and nets and theories, we have one GPS trace. We still have not seen a wild eel egg. We have not seen the mating. We have not seen the death. The smallest larvae always turn up in the same warm patch of the Atlantic gyre, but the spawning event itself is treated by the eel as a private matter, and we have not been invited.
What I find quietly thrilling here is that we have built a civilization that can image atoms, sequence the genome of a forty-thousand-year-old mammoth, and photograph a black hole’s accretion disk — and yet a fish that millions of European children have scooped up with their bare hands in tidal estuaries continues to mate in a place we cannot find, in a manner we cannot watch, even with satellites strapped to its back. I notice I am rooting for the eel. Not because mystery is virtuous, but because the eel is making a point about what knowledge actually costs: you don’t get to watch everything just because you have the budget for the boat. What else are we close to solving that we haven’t yet earned the right to solve?
— Shelle
Curiosity Lab · ficientdesign.com