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When Dr. Seuss’s The Lorax came out in 1971, it quickly took the world by storm.

The plight of all the animals that lost their homes when the greedy Once-ler cut down all the Truffula trees—and the trees’ comically mustached champion, the Lorax— resonated deeply with many worldwide, inspiring an entire generation to care about the environment. But many scientists think Seuss’s book wasn’t just a fable. The Lorax and its precious truffula trees are real, and they’re now facing the completely non-fictional threat of extinction.

In September of 1970, Theodor Geisel, aka Dr. Seuss, was trying to write a book about conservation, but he felt blocked. So, he traveled to Kenya to clear his head.

That’s where he likely first saw the patas monkey and witnessed its close relationship with whistling thorn acacia trees. Patas monkeys are kinda goofy-looking primates that wander African savannahs in groups. Unlike other monkeys, they’re quite comfortable on the ground, so if they feel threatened, they generally just run rather than scamper up a nearby tree.

And that’s probably because they can book it at a whopping 55 kilometers per hour—fast enough to outpace most predators. That speed is thanks to their super long legs, which evolved, in part, because of their fondness for acacia trees. Acacias are a common but somewhat spread out food resource, so the monkeys have evolved to walk great distances—kind of like us.

And that allows them to rely on the trees for more than three-quarters of their diet. Part of what they rely on is the gum from the tree itself, which is rich in minerals like calcium, iron, and manganese. But a lot of their diet actually comes from the ants that live inside the large, swollen thorns that make the tree look so Seussian.

The ants help discourage large herbivores from eating the trees, but patas monkeys love them. These treat-filled thorns are too tough for smaller species of monkey to break open. And that works out just fine for the patas monkey, which could get all the protein it needs from the ants alone.

And because the trees and their ants are available all year, they’re a more stable, reliable food source than the fruits that other monkeys prize. The only catch is that it takes a lot of gum and ants to feed the somewhat large monkeys— males weigh in at around 12.5 kilograms, while females are about 6.5. So the monkeys can only make their diet work if there are lots of acacias to feed from—hence those long limbs that let them move quickly between patchy groves.

Normally, there are plenty of these trees for the monkeys to find— or, at least, there were plenty of them back in 1970, when Geisel arrived in Kenya and found the inspiration he needed to write The Lorax. It’s not 100% certain that he based the Lorax and their Truffula trees on patas monkeys and their favorite acacias, but researchers have pointed out several lines of evidence that support the idea. There’s the coincidence of timing, of course— that he found his muse in an area of Kenya where the trees and monkeys were a common sight.

And the trees in the book do look awfully similar to whistling thorn acacias, down to the way they stand somewhat alone in patches surrounded by a grassy landscape. Oh, and the Lorax sure looks a lot like a patas monkey. When researchers ran a facial similarity analysis, the Lorax looked more like the patas monkey than like the most similar Dr.

Seuss character, or even like other monkeys. Unfortunately, real life seems to be repeating the book’s story. When Giesel visited the Laikipia plateau in Kenya for inspiration, whistling thorn acacia trees were all over the place.

When he wrote about the trees disappearing, that was an imagined future. But in the decades since, they’ve declined dramatically. That’s in part because another tree—one that’s a lot less palatable—is out-competing the acacias.

The reasons behind this hostile takeover are complex. One problem is that human use of these landscapes has shifted the type and intensity of animals consuming plants. In reserves like the one studied, the trees are subject to higher concentrations of larger consumers like elephants.

Their voracious appetites can spell doom for small trees and seedlings. And those animals are also relying more heavily on the trees in recent years because climate-change-driven droughts have reduced the amount of grass available. But getting rid of these big herbivores isn’t the answer, either.

When scientists tried removing big herbivores from areas in Kenya for a 2014 study, seedling survival of the whistling thorn acacia plummeted because smaller animals that eat them, like mice, flourished. And scientists are becoming increasingly concerned about the effects of wildfires, which are happening more often because of increasing temperatures and decreasing rainfall. When the land burns, the acacias often lose their symbiotic ants, which makes them even more vulnerable to herbivores.

So there’s a lot of debate about the best path forward to ensure the long-term survival of these vital trees in the face of climate change. In the meantime, their decline is affecting their primate loraxes. Patas monkeys aren’t considered endangered yet, but their populations have been declining and their range has been contracting in recent decades, likely in response to the disappearing trees.

And if the acacia trees disappear from Kenya, then the monkeys will, too. Which means Geisel’s final message in The Lorax couldn’t be more fitting: “Unless someone like you cares a whole awful lot, nothing is going to get better. It's not." Thanks for watching this episode of SciShow, which is sponsored by Skillshare.

This week, we’re working with Skillshare to highlight classes we think you’ll like. And if you enjoy imagining what it must have been like for Dr. Seuss to translate the patas monkey into the lorax, I think you’ll get a lot out of this Character Design class taught by Hayden Aube where he teaches you how to create a character from any land animal.

He’s an experienced teacher and opens the class with recommendations on how to get the most out of it based on behavioral science and his own experience. And I actually learned a lot about anatomy in this class. He approaches drawing from a scientific perspective so that you’re not just replicating his lessons, but you can go out and figure out how to draw any animal or character you want to.

If you want to check it out, we’ll link to this class in the description as well as an offer from Skillshare to get 2 months of access to all their classes for free. Skillshare has over 20,000 classes on everything from animation to web development. So let us know what classes you decide to take, and know that when you’re learning on Skillshare, you’re also helping to support SciShow, so thanks! [OUTRO ♪].