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Anyone who remembers that King Philip came over from Germany stoned owes a debt of gratitude to 18th-century polymath Carl Linnaeus. That cannabis-scented mnemonic device from high school biology class refers, of course, to the taxonomic ranks of kingdom, phylum, class, order, family, genus, species—the system of classifying the natural world from least to most specific. We are genus homo, species sapiens because of Linnaeus’ Systema naturæ, which, when published in 1735, brought some order to our sprawling family trees—not only for us, but the trees, too, and every living thing in between.
After classifying who belongs where, Linnaeus, in 1749, set out to compose a massive thesis about who eats what. Published in Latin as Pan Svecicus, this wide-ranging botanical study of the Nordic countryside sought to give Swedish farmers hard data on which plants their grazing animals liked to munch on. It was a remarkable doorstop of a work that was far ahead of its time, Håkan Rydin, an emeritus professor of plant ecology at Sweden’s Uppsala University tells me. By examining the interplay between plants, the animals that ate them, and the places they grew, Linnaeus unwittingly conducted the first work of modern ecology.
But Pan Svecicus was also a mess.
As one of Linnaeus’ lesser-known works, written originally in dense Latin, Pan Svecicus presented a staggering amount of data that Linnaeus never really got around to analyzing, says Rydin. It describes 2,325 experiments involving 643 different plant species, but largely ignores what useful things the data suggest. So, Rydin and co-authors recently undertook a study of their own, which was published in September, to bring some tidiness to Linnaeus’ little known work.
Within the thickets of information recorded in the Swedish countryside by Linnaeus and dozens of his students, Rydin’s team discovered some interesting facts that for 275 years had gone more or less unnoticed.
For one thing, it turns out that pigs are exceptionally picky eaters. They ate only 32 percent of the 204 plant species they were fed in Linnaeus’ study. On the other extreme, goats eat just about anything, consuming 85 percent of the flora they were offered. Sandwiched in the middle were horses, cows, and sheep. What the ruminant animals chose to eat, Rydin discovered, overlapped significantly, but the pigs had tastes that deviated from that norm. This was a surprising result, says Rydin. As omnivores, pigs weren’t thought to be very selective, then or now. But the opposite is true. Their rooting behavior, in fact, often leads them past green leaves to the roots and worms that Linnaeus’ data showed was more to their liking.
The farm animals generally preferred plants from the orders of Fabales—which contains species such as peas, beans, alfalfa, and clover—and Poales—which includes the staple grains like rice, wheat, and barley. But pretty much all of the animals steered clear of things like sage, mint, basil, poppies, and buttercups—plants of the orders Lamiales and Ranunculales. Horses and cows, meanwhile, were keener to avoid plant species presumed toxic to livestock, such as northern water hemlock, unlike goats and pigs, while all animals showed a preference for species that are today considered nutritious.
This confirmed what scientists knew back in the 18th century. But back then, they could not have known why: that the animals are drawn to nitrogen fixing mutualists—or small bacteria living symbiotically with legumes—that were ringing the dinner bell. Had Linnaeus analyzed his data with current statistical methods, he might have uncovered these facts, which would have helped farmers select better plant species for their grazing meadows. “But this was long before biologists knew about statistics,” says Rydin.
Linnaeus unwittingly conducted the first work of modern ecology.
So, what compelled Rydin and his team to disgorge these bits of barnyard wisdom from a chaotic study that’s been collecting dust for nearly 300 years? Basically, it was simple curiosity stoked by another project Rydin was working on, he tells me. While preparing a text on Linnaeus and ecology for Swedish schools, he ran across a handful of references to Pan Svecicus—a bit of Linnaean lore that he hadn’t previously seen.
Particularly stirring to Rydin was a 2007 paper called “Linnaeus and the Economy of Nature,” by Frank Egerton, which identified Pan Svecicus as “one of the earliest, if not the earliest, series of experiments on an ecological question, and surely the earliest such large-scale quantitative experiments.” This set Rydin on a quest to find out how Linnaeus interpreted the results of his experiments—and then he discovered that he hadn’t.
“We realized that [Pan Svecicus] summarized what was already known at the time about the feeding of these animals, and the text of the thesis was not at all based on the results of the investigation,” Rydin told me in an email. “So, we had to find out for ourselves.” Why Linnaeus hadn’t analyzed his data, says Rydin, remains something of a mystery. On a practical level, quantitative analysis wasn’t really a thing in Linnaeus’ time, Rydin says. Plus, Linnaeus was a busy guy. As a man who wore many hats—university professor, physician, botanist, mermaid researcher—it’s possible he just didn’t have the time to reflect on what the data could tell him. He just tabulated the data and had to move on to other things, Rydin suggests.
Equally mysterious to Rydin was why no one else had yet applied the more modern tool of quantitative analysis to Linnaeus’ data. Rydin, however, lays no claim to his interpretations as being definitive. “Please, bear in mind that this is 18th-century research, before strict scientific protocols were invented,” he said. “We do not claim that our interpretations about what the animals prefer are scientifically correct, but they show what Linnaeus could have concluded if he had had statistical tools.”
As lacking in modern refinements as Pan Svecicus may be, the method behind it nonetheless anticipated the modern academy’s approach to writing scientific papers. “Scientists in those days worked mostly on their own,” said Rydin. “So, we were most surprised by how Linnaeus structured the research by tasking a number of his more senior pupils—much like postdocs—and these in turn had more junior students to help. How could he otherwise have gathered more than 2,300 observations?”
That is certainly a task of a different order. 
Lead image: PK Designs, Marina Akinina, QuirkCraft Studio and Irina Velikanova / Shutterstock and Pixabay
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