A Science Writer Makes the Case for Embracing Migration

The Edith’s checkerspot butterfly is a delicate insect, with a wingspan less than a thumb’s length and a tendency to hide from the rain. For many years, these butterflies were thought to be “the entomological equivalent of homebodies,” science journalist Sonia Shah writes in her new book, The Next Great Migration. Researchers hardly ever saw them stray far from the places where they were born. As cities encroached on the species’ habitats and climate change made it harder to survive, many believed they were destined for extinction.

But in the mid-1990s, a Texas biologist named Camille Parmesan made a startling discovery. After gathering data on their habitats, she found that these fragile little animals weren’t homebodies at all: they had been shifting their range in response to climate change, moving north and to higher altitudes in order to survive. Parmesan’s discovery brought about a revolution in climate science, and soon researchers found legions more species that were migrating in response to climate change, including corals, red foxes, and even fungi. 

This is the anecdote that opens The Next Great Migration, an ambitious work of journalism that argues migration has played a vital role in our planet’s history. For centuries, Shah writes, scientists and political leaders have portrayed migration as something “unnatural” and “disruptive,” clinging to the idea that people, plants, and animals aren’t meant to move. But in reality, she argues, movement is completely natural, and we’ve been doing it for millennia. And while it’s sobering to know that our changing climate has disrupted so many species’ way of life, Shah sees reason for hope. “A wild exodus has begun,” she writes. “It is happening on every continent and every ocean.” In the coming years, as climate change threatens human and animal habitats, migration “may be our best shot at preserving biodiversity and resilient human societies.” In other words, it has the power to save all our lives.

Shah makes her case by moving nimbly between scientific history, scenes from her travels with ecologists, and occasional stories from refugees around the world. She takes a reportorial approach, mostly staying out of the picture, but she does briefly wrestle with her own experience as a daughter of Indian immigrants who spent many years feeling “somehow out of place” in the United States. “As a child, I was ashamed of even small things, like my preference for suspiciously fruity strawberry ice cream over the unimpeachably American chocolate for which the other children clamored,” she writes. It’s only after starting to research migration as an adult that she begins to feel like she truly belongs.  

Scientists have been depicting migration as a destructive force since at least the 18th century, Shah writes, when the Swedish botanist Carl Linnaeus invented modern taxonomy. Linnaeus believed that all the world’s species had left the Garden of Eden long ago—and then stayed put for centuries. The notion of mass migration was unthinkable: like many of his contemporaries, Linnaeus assumed birds hibernated for the winter, diving to the bottom of lakes or hiding out in caves. Accordingly, Linnaeus developed a system for classifying plants, animals, and people based on their geographic location. Humans who lived on different continents, he believed, were separate subspecies. It was a false idea, but a politically expedient one: “From a colonial perspective, it was more convenient to cast foreigners as so strange as to be unrelated or perhaps not even human at all,” Shah notes. Using Linnaeus as a jumping-off point, Shah surveys the vast legacy of scientific xenophobia, showing how the idea that migration is unnatural went on to influence eugenicists and the Nazis, along with prominent biologists and even U.S. presidents.

“Migration is not an exception to the rule,” Shah writes. “We’ve been moving all along.”

Along the way, Shah offers an important reminder that the history of American conservation movements can’t be separated from that of anti-immigrant politics. Madison Grant, who played a key role in developing the national park system, was also a white supremacist who shaped U.S. immigration policy. John Tanton, a conservationist who started a chapter of the Audubon Society, was a racist thinker who launched a network of anti-immigration groups that continue to influence the Trump administration today. Even David Brower, the famous Sierra Club leader, tried to push his organization to adopt an anti-immigration platform as recently as the late 1990s. (Tanton also participated in that effort.) Brower was one of a group of environmentalists at the time who were obsessed with the false idea that migration would lead to overpopulation and destroy the planet.  

In the latter half of the book, Shah presents a skillful rebuke to the long line of scientists, environmentalists, and elected officials who’ve advanced such xenophobic thinking. In recent years, scientists have begun to discover the full extent of ancient human migration: we now know that early humans traveled out of Africa in several waves and back again, moving continuously between continents throughout the course of history. “Migration is not an exception to the rule,” she writes. “We’ve been moving all along.”

She also wades into the debate about invasive species, arguing that migratory plants and animals have been unfairly maligned. It turns out many scientists think that only about one percent of nonnative species pose a threat to resident plants and animals—the rest tend to increase biodiversity, if they have any impact at all. Moreover, leading biologists say that migration “most likely evolved as an adaptive response to environmental change.” That’s why creatures like the checkerspots move as the earth gets warmer, and why migration will play a critical role in the planet’s future.

In this last part of the book, you get the sense that Shah is rushing a little—I wish she’d spent more time exploring the complicated contemporary science of wildlife migration. She also gives a brief overview of the ways we’re seeing climate change influence human movement today, but she doesn’t go into much depth on the topic. Despite the book’s title, The Next Great Migration focuses more on the past than on the future. 

But maybe it’s inevitable that you can’t cover everything when you’re trying to wrangle hundreds of years of human and environmental history into a book that’s just over 300 pages. Shah has done a remarkable job, distilling complex ideas from a variety of disciplines into concise and elegant prose. She has a knack for summing up a big idea in a punchy sentence, but she also knows how to linger on a lovely scene, transporting the reader from the jungles of Hawaii to the Himalayan foothills.

Prior to The Next Great Migration, Shah wrote a book about pandemics, and she admits that her work in that field once contributed to her “sense of movement as aberrant, something anomalous that needed to be examined and explained.” In the past few months, politicians have been especially eager to exploit Americans’ heightened fear of movement. We’ve seen Trump use COVID-19 as an excuse to push through draconian measures—like indefinitely closing the border to asylum seekers—that have nothing to do with stopping the virus.

In this time of rampant xenophobia, Shah’s book offers a call to “reclaim our history of migration and our place in nature as migrants like the butterflies and the birds.” It’s a powerful invitation, and one that’s never been more urgent.

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