Olivia: Everything you think you know about 'invasive species' is probably wrong. The phragmites reeds you see choking wetlands? They might be doing more good than harm. Jackson: Hold on, really? I thought those were public enemy number one for local ecosystems. Olivia: That’s what we’re taught. But what if the very idea of a pristine, 'native' ecosystem is a complete fantasy? What if all of life, for all of time, has been on the move? Jackson: Okay, my brain is already starting to pretzel. You’re saying movement isn't a crisis… it’s just… life? Olivia: It’s the fundamental rule of life. This whole radical idea comes from Sonia Shah's incredible book, The Next Great Migration: The Beauty and Terror of Life on the Move. Jackson: And Shah is the perfect person to write this, right? She's a top-tier investigative journalist, but her parents were Indian immigrants. She's lived this tension between worlds her whole life, which gives the book this amazing blend of hard science and deep empathy. Olivia: Exactly. It was a finalist for the PEN/E.O. Wilson Literary Science Writing Award for a reason. It completely reframes how you see the world. And it all starts with a creature you'd never expect to be a globetrotter: a tiny butterfly.

Jackson: A butterfly? Not exactly what I picture when I think of a "great migration." I'm thinking wildebeests, caribou... something epic. Olivia: Well, this story is epic in its own way. It’s about the Edith's checkerspot butterfly. In the 1980s, a scientist named Camille Parmesan was studying them for her PhD. She was in Southern California, and the butterflies were disappearing. The assumption was simple: climate change and urban sprawl were killing them off. End of story. Jackson: A classic, tragic tale of human impact. We hear that a lot. Olivia: Right. But Parmesan was a meticulous scientist. She collected years of data on where the butterflies were and where they weren't. And when she analyzed it, she found something astonishing. Yes, the populations in the south, where it was getting hotter and drier, were winking out. But the populations in the north, and at higher, cooler elevations in the mountains, were thriving. Jackson: Huh. So they weren't just dying. Olivia: They were moving. Parmesan had this incredible "My goodness!" moment, as she put it. The butterflies were shifting their entire range northward and upward, chasing the climate that suited them. They were migrating, not over a season, but over generations. Jackson: Wow. So the entire species was picking up and moving house. That’s a wild concept. Olivia: It gets wilder. Shah points out this isn't just butterflies. Take the Himalayas. We think of them as this impassable, permanent barrier. But scientists studying the tree line there found that since 1880, the forests have been steadily climbing the mountainside. Jackson: A whole forest is climbing a mountain? How is that even possible? Olivia: Slowly, generation by generation. The trees at the upper edge produce seeds, and those seeds take root just a little bit higher up, where the climate is now survivable. We're talking nineteen meters uphill every single decade. And everything that lives in the forest—the rhododendrons, the insects, the birds—is climbing with it. Even mosquitoes have appeared in Tibet for the first time ever. Jackson: That's incredible. It’s like the whole planet is this slowly churning, rearranging puzzle. But I have to push back a little, Olivia. That's nature. It’s fascinating, but human migration feels different. It’s messy, it’s political, it causes conflict. We see it as disruptive for a reason, don't we? Olivia: That is the absolute heart of the book. Shah’s argument is that we see human migration as a problem precisely because we've built our world on a fundamental misunderstanding of that natural law. We believe in a world where things—and people—belong in a specific place. And anyone who moves is an anomaly, a disruption, a threat. Jackson: A migrant is seen as a bug in the system. Olivia: Exactly. But what if the system itself is movement? Shah forces us to ask: where did our idea of a static world even come from? And the answer, surprisingly, takes us back to the 1700s.

Olivia: To understand our modern fear of migration, you have to understand a Swedish botanist named Carl Linnaeus. He was a man obsessed with order. He wanted to categorize every living thing on Earth and put it in its proper box. Jackson: The guy who gave us Kingdom, Phylum, Class, Order… I remember that from high school biology. He’s basically the inventor of tidy labels for nature. Olivia: He is. And his system, Systema Naturae, was revolutionary. But it had a hidden, powerful assumption baked into it: that every species had a fixed place of origin, a homeland. A palm tree belonged in the tropics, a polar bear in the arctic. They were created there, and that's where they should stay. Movement wasn't part of the plan. Jackson: So he created a world map where every creature was pinned to a specific spot, like a butterfly in a display case. Olivia: A perfect analogy. And this idea—that life is sedentary—became the bedrock of Western science for centuries. It seeped into how we thought about people, too. When European explorers encountered people in Africa or the Americas, they didn't see cousins who had adapted to different climates; they saw fundamentally different types of humans, as fixed to their continents as the plants and animals were. Jackson: And that's a very short leap to creating hierarchies. To saying 'our type' is better than 'their type'. Olivia: It’s a direct line. This thinking paved the way for so-called "race science." And Shah gives this absolutely chilling example of where that led. In the early 1900s, one of the founders of the Bronx Zoo, a man named Madison Grant, decided to create an exhibit to showcase this idea. Jackson: An exhibit? What did he do? Olivia: He put a man from the Congo, named Ota Benga, in a cage in the monkey house. He was displayed right next to an orangutan, presented to the public as a "missing link," a less-evolved form of human. The New York Times ran headlines about it. Crowds flocked to see him. Jackson: Wait, they put a man in a cage with an orangutan and called it science? That's just… monstrous. It's hard to even comprehend. Olivia: It’s horrifying. And Madison Grant, the man behind it, would go on to write one of the most influential racist books of the 20th century, The Passing of the Great Race. It argued that "Nordic" people were the superior race and that immigration from Southern and Eastern Europe was diluting America's greatness. Jackson: But surely real scientists, like Darwin, pushed back against this? Darwin's whole theory is about change and adaptation, not things being fixed. Olivia: You'd think so. And Darwin did argue that all humans were one species and that differences were superficial. But his ideas were largely ignored or twisted. The "scientific" establishment was dominated by men like Grant. They developed biased intelligence tests at Ellis Island that "proved" the vast majority of Jewish, Italian, and Russian immigrants were "feeble-minded." Jackson: Let me guess, the tests were full of questions only an American would know. Olivia: Questions like "Who was the Union commander at Mobile Bay?" They were designed to produce a result, and that result was used to build a political wall. These eugenicist ideas, born from Linnaeus's static view of the world, directly led to the 1924 Johnson-Reed Act, a US immigration law that slammed the door on millions, establishing quotas based on national origin. Jackson: And that had devastating consequences, especially leading up to World War II. Olivia: Devastating. The book notes that Adolf Hitler himself wrote a fan letter to Madison Grant, calling his book "my bible." The ideas that caged Ota Benga in the Bronx Zoo provided a "scientific" blueprint for the Holocaust. It's a direct, terrifying lineage from a botanist's filing system to global catastrophe. Jackson: It's a bleak history. It almost feels like we're hardwired for this fear of the 'other,' of the migrant. Olivia: But Shah argues we're not. And this is where the book turns from this dark history to a place of incredible, radical hope. The final, and most powerful, part of the book reframes this entire debate. It's not about a crisis to be managed; it's about a fundamental law of life we must relearn.

Jackson: Okay, so if we're not hardwired for this fear, how do we unlearn it? Where does the hope come from? Olivia: The hope comes from returning to biology, but with a new understanding. Shah introduces us to the work of an ecologist named Hugh Dingle, who came up with what you could call the 'Migrant Formula.' Jackson: A formula for migration? That sounds complicated. Olivia: It's surprisingly simple. It's a ratio: the time it takes for a species to reproduce versus the time its environment remains stable and supportive. When the environment changes faster than you can adapt in place, you have two choices: you move, or you die. Migration isn't a choice; it's a mathematical necessity for survival. Jackson: Move or die. That’s stark. Olivia: And Shah gives us two perfect, heartbreaking, and hopeful stories to illustrate this. The first is the Bramble Cay mosaic-tailed rat. Jackson: Never heard of it. Olivia: Almost no one has, because it's gone. It lived on one tiny, low-lying island in Australia. As climate change caused sea levels to rise, storm surges began washing over the island, killing the plants the rats ate. They were trapped. They had nowhere to migrate. In 2019, it was declared officially extinct—the first mammal known to be wiped out by climate change. It died because it couldn't move. Jackson: Wow. So the wall, in this case, was the ocean. It was a death sentence. Olivia: Exactly. Now, contrast that with the story of two women, Sophia and Mariam. They were refugees who fled persecution in Eritrea, spent years in horrific camps, and were finally resettled in a run-down neighborhood in East Baltimore. They faced immense hardship—language barriers, poverty, a hostile political climate. Jackson: A completely different kind of wall. Olivia: A different kind, but just as real. The book describes the author taking them to see Christmas lights one evening. On the way back, as they drive into their neighborhood, Sophia, who has been through unimaginable trauma, looks at her apartment building and whispers, "My home." Jackson: That gives me chills. After everything, she found a place. Olivia: She found a place. She survived because she could move. The rat went extinct because it couldn't. Shah's point is that this is the fundamental choice facing life on a changing planet. The wall, whether it's an ocean or a border fence, leads to stagnation and death. Movement is resilience. Movement is life. Jackson: So this is the 'Next Great Migration' the title talks about. It's not just one group of people. It's potentially all of us, all of life, having to adapt to a world in flux. Olivia: Precisely. Climate change is turning up the heat on that 'Migrant Formula' for everyone. Shah argues we can either build more walls and create more tragedies like the Bramble Cay rat, or we can start designing a world that allows for safe passage. A world that recognizes migration not as a threat, but as our most essential survival strategy.

Jackson: It really forces you to rethink everything. The idea that we're fighting against a fundamental law of nature is… sobering. Olivia: It is. Shah's ultimate message is that we've built our modern world on a dangerous fantasy of permanence. We treat borders on a map as sacred and the people crossing them as a threat. But biology, history, and a changing climate are all screaming the same thing: the real threat isn't the migrant; it's the wall. Jackson: That’s a powerful way to put it. It makes you question the very word 'home.' Maybe home isn't a fixed spot on a map, but the ability to move to a place where you and your family can be safe and thrive. Olivia: I think that’s exactly the shift in perspective she’s calling for. It’s a profound and challenging idea, but also a deeply hopeful one. It suggests a future built on fluidity and empathy, rather than fear and exclusion. Jackson: It’s a future where we see a butterfly shifting its range, a forest climbing a mountain, and a family seeking refuge not as separate problems, but as part of the same beautiful, and sometimes terrifying, story of life on the move. Olivia: It's a story we're all a part of. And it's a conversation that's more urgent than ever. We'd love to hear your thoughts. In a world that's constantly changing, what does the word 'home' mean to you? Let us know on our social channels. Jackson: We're really curious to hear what you think. Olivia: This is Aibrary, signing off.