Why Do Humans Move?

We All Move

The science and politics of migration.


To the memory of Christopher Columbus,” reads the inscription to the large Columbus Fountain in Washington, D.C., “whose high faith and indomitable courage gave to mankind a New World.” The monument was erected in 1912, and one cringes reading those words now. Columbus did not give mankind a New World. As the statue of the Native American man kneeling by Columbus’s side suggests, that world was already fully possessed by humanity.

Nearly everywhere European “discoverers” sailed, in fact, they met people who had discovered those lands long before them. The Americas had already been discovered; so had Australia and New Zealand and the Arctic North. Even seemingly remote Pacific islands were inhabited by the time Europeans arrived. It’s bracing to realize just how few truly empty places European sailors found—“islands and ice, mostly,” according to the Yale cartographer Bill Rankin. Not counting the frozen continental land at the poles, Rankin calculates that the uninhabited areas discovered by seafaring Europeans amounted to only 0.14 percent of the world’s land.

How did humans get to all those places? This question tormented European thinkers for centuries. For Carl Linnaeus, the Swedish botanist who established the system we use today to classify species, God must have done the work. After creating the Garden of Eden, God then dispersed humans across the planet, and there they stayed, awaiting European discovery.

Linnaeus’s theory offered a neat solution but not a durable one. Later scientists leaned toward the theory that humans must have wandered aimlessly to all these far-flung locales. How they managed this in the case of Polynesia was hard to imagine, given the distance of some of its islands from any large landmass. The prominent 20th-century anthropologist Ralph Linton insisted that the first Polynesians must have arrived “as a result of accidental drifts”—seafarers from the east, blown far off course, who had somehow fortuitously hit land. The Norwegian ethnographer Thor Heyerdahl offered a weirder variant on this theory: A “race of white gods” originally from Eurasia had drifted west to Polynesia from the Americas. In 1947, to show this could be done, he built a balsa raft named Kon-Tiki, equipped it with a radio, and allowed the wind and current to carry him 4,300 miles from Peru until he ran aground on a coral reef in French Polynesia.

What Linton and Heyerdahl couldn’t believe was the story that the people of the Pacific themselves told: that they had sailed the wide ocean on purpose. To prove it, in 1976 a Micronesian navigator named Mau Piailug set out in an 18th-century-style vessel from Hawaii. He took neither charts nor modern instruments. Instead, he used wayfinding, a traditional form of navigation relying on the position of the stars, the feel of ocean swells, other natural observations, and prodigious feats of memory. Piailug reached Tahiti in 34 days. In the next three decades or so, his ship completed nine more voyages, hitting far-off targets with pinpoint accuracy.

The mystery of Polynesian origins no longer baffles anthropologists. We have ample evidence to confirm that Piailug was right: Polynesians came first from Asia, and not by accident. Yet the mindset that obscured this truth for so long persists. We find it easy to imagine migrations as one-off accidents: canoes set adrift, Siberian hunters taking a drastically wrong turn at the Bering Strait. We find it far harder to imagine people moving intentionally, regularly, and as part of the natural course of things.

This prejudice against motion is the subject of The Next Great Migration: The Beauty and Terror of Life on the Move, by the science journalist Sonia Shah, and it’s one she has had occasion to contemplate for decades. As a New York–born Australian citizen descended from Gujaratis, Shah has lived with “an acute feeling of being somehow out of place.” Perhaps that’s why she has made a career studying insects, parasites, and bacteria crossing borders, including in her prescient 2016 book Pandemic: Tracking Contagions, From Cholera to Ebola and Beyond. Now, in The Next Great Migration, Shah scales up. It’s not just microbes that move, she notes, it’s everything: birds, rodents, trees, continents, and, importantly, humans. Accepting that means learning to see motion as normal rather than exceptional. And it prepares us to meet the future that climate change will bring—in which people will have to migrate as never before—with equanimity and humanity.

The book’s title points toward this future, but Shah is mainly concerned with showing how common human and animal motion were in the past. Looking backward is important because, in her view, we have yet to fully dispel what she calls “the myth of a sedentary world.” Again and again, scientists have taken fixity as normal and have been surprised to discover that, in fact, things move. Undergirding this bias toward stability, Shah argues, is a widely felt sense that plants, animals, and people have proper places to which they belong. That’s what we’re feeling when we say things are “out of place.” According to Shah, that sense of belonging often leads us awry.

Take lemmings. If you know one thing about them, it’s that they are suicidal, marching maniacally over cliffs into the unforgiving sea. It is, on the face of it, curious behavior, but in 1924 the British Journal of Experimental Biology explained it as a population-culling mechanism. Lemmings reproduce, overgraze, and then, facing starvation, choose death before dishonor, “ecstatically throwing themselves over the ends of railway bridges.” The 1958 Disney documentary White Wilderness seared the notion of mass suicide into many tender minds with its footage of dozens of lemmings tumbling into the Arctic, with only a “small handful” of their more cautious compatriots surviving.

But White Wilderness was staged, as Shah points out. Those lemmings didn’t jump; they were pushed. And the reason is that lemmings are not suicidal. What they are is exuberantly migratory, capable of adventurously seeking out new locales—even crossing small bodies of water—in response to population pressures. It is typical of a “nonmigratory, closed-border world,” Shah writes, that most people assume lemmings on the move are seeking death when they are actually seeking new lives.

To be fair, there are many reasons scientists have had such difficulty comprehending migration. It’s hard to track, say, a monarch butterfly from Ontario to Michoacán—borders intercede. Before the 19th century, it was anyone’s guess where birds went in the off-season. The first English-language treatise on the topic, written by a leading 17th-century physicist, concluded that they went to the moon. It wasn’t until 1822, when a stork turned up in a German village with a Central African spear sticking through its neck, that ornithologists truly grasped the nature and range of these migratory routes. And throughout the 20th century and into the 21st, the precise routes of many species remained elusive.

But Shah sees more than just ignorance afoot. Darker motives peek out from under respectable scientific theories. Because Linnaeus believed in a stable biological world, he found it easier to imagine that birds hibernated in the winter—vanishing to unknown hiding spots—than that they crossed ecological zones. He also found it easier to believe, therefore, that humanity was divided into five racial subspecies, each with its own proper climate and continent.

Racism goes hand in hand, Shah shows, with belief in a sedentary world. In the 20th century, Madison Grant, a founder of the Bronx Zoo, believed animals to be hemmed in by their habitats. The alarming exception, for Grant, was the human, the “most cosmopolitan of animals.” Human mobility wasn’t a good thing, in his view. As he warned in his best-selling treatise of 1916, The Passing of the Great Race, the migration of peoples away from their customary climates would lead to intermarriage and the enfeeblement of the white race.

Grant’s theories resonated in the United States of the early 20th century, heavily invested in both racial segregation and empire. Former president Theodore Roosevelt counted Grant as a close friend, traded notes with him about various racial groups’ skull shapes, and told him that “all Americans should be sincerely grateful to you” for writing The Passing of the Great Race. Grant’s work eventually helped inspire a US immigration law in 1924 to heavily restrict migration from countries outside Western and Northern Europe.

Grant also met with the acclaim of the Nazis, who published The Passing of the Great Race in German. Adolf Hitler read it with enthusiasm, calling it his “bible” in a letter to Grant. The Nazis obsessed over biological stability in all realms. They sought, Shah writes, to “banish ‘foreign’ plants from their gardens,” such as the seemingly innocuous small balsam, which they deemed a “Mongolian invader.” Meanwhile, they protected “native” species and made killing an eagle punishable by death.

Ultimately, Shah argues, how you view plants and animals relates to how you view people, and for her this reveals the larger political and ethical quandaries created by the myth of a sedentary world. You see the small balsam as an invader, and maybe you feel the same way about the Poles. You see migrating lemmings as senseless hordes that don’t value their own lives, and you’re all the more ready to say the same of Syrian refugees crossing the Mediterranean.

Luckily, there’s never been a better time for lemming revisionism. Two technologies in particular, Shah notes, have recently transformed our understanding of migration. The first is the Global Positioning System tracker. The second is the extraction of DNA from the human petrous bone, found near the ear. Taking their lessons together, she argues, should explode the myth of a sedentary world and show how ill-conceived today’s closed border politics are.

The US Department of Defense began launching GPS satellites in the 1970s and had a full complement of them in orbit by 1993. Yet civilian scientists using the system could only calculate position roughly, because the Pentagon intentionally degraded its publicly available signal to confound America’s adversaries. Shortly after midnight on May 1, 2000, it stopped doing that, essentially upgrading every GPS user in the world to a premium account. The subsequent boom in GPS technologies yielded lightweight, solar-powered tags that scientists could affix to migrating animals.

Nineteenth-century scientists depended on freak events like storks impaled with African spears to glimpse migration’s mysteries. Now they can spear any stork they wish and get spear-cam updates every five seconds. The results have been “stunning,” Shah writes. The Arctic tern, despite its name, flies annually from the northern reaches of the planet to Antarctica, a nearly 60,000-mile journey. Those “native” German eagles the Nazis were so intent on protecting? You can find some in Zambia in the winter. Migratory animals move a lot, it turns out, often in clever, complex, and profoundly weird ways.

Humans do, too. The old idea was that ancient humans had wandered out of Africa across land bridges and stumbled onto unlikely habitats, spinning off from the rest of humanity and founding new populations. But that was before 2015, when the anthropologist Ron Pinhasi and his colleagues showed that the unusually dense petrous bone could yield a trove of DNA from archaeological specimens. With improved extraction and DNA sequencing techniques, the petrous bone has allowed a much clearer view into the distant past. We no longer think ancient migrants accidentally reached new locales on onetime, one-way journeys. Rather, it now appears, they crossed back and forth, migrating in multiple and many-directional streams. The image of humanity as a tree with diverging branches, Shah writes, makes sense only if we imagine those branches frequently curling back and fusing with one another.

“Populations today almost never descend directly from the populations that existed in the same place even 10,000 years ago,” the paleogeneticist David Reich explained. That’s because people mix and move relentlessly. “I think that’s a very profound insight,” he added. “It should change the way we see our world.”

It should, but will it? Shah points out a painful irony: Just as Reich’s fellow scientists were getting the hang of grinding up petrous bones to reveal how often humans moved in the past, politicians started frantically erecting fences and walls with the hopes of getting them to stop doing it today. The year 2015—the same year as the Pinhasi group’s paper—saw “an unprecedented surge in construction of new border walls,” Shah writes. Barriers shot up on the European side of the Mediterranean to block refugees from the Middle East. The new barricades have cut down on border crossings, though at the cost of making the already hazardous journey far more so. In 2015, one migrant in 270 died trying to reach Europe by sea; by 2018, it was one in 52.

Impermeable borders kill, and they also impoverish. Consider Haiti, once one of the most profitable patches of land on the planet but now one of the world’s poorest countries. It has suffered tremendously at the hands of such powerful nations as France and the United States, to the point where economic fixes are hard to come by.

Yet there is one strategy that has helped: letting people leave. The New York University economist Bill Easterly pointed out that 82 percent of Haitian escapes from poverty can be credited to migration to the United States. Unfortunately, the United States has grown less hospitable to this and has recently aggressively deported Haitians, in effect throwing them off the economic ladder. “Why do we need more Haitians?” Donald Trump reportedly once asked legislators. “Take them out.”

The typical response to nativists like Trump by pro-migration advocates is to plead exigency. Haitians have good reason to claim status as political or economic refugees, essentially arguing that they need a new country because theirs is broken. Shah sympathizes, but her book makes a different argument. The Next Great Migration softly rejects the idea that anyone “belongs” anywhere—that anyone has a country in the first place. By its terms, Haitians should not have to plead that “their” country is unviable to enter another. To do so would be to give too much credence to the myth of a sedentary world, where migration is an exceptional act born of desperation.

For Shah, migration has always been the rule rather than the exception, but it will become even more common as the planet warms. The low-lying country of Bangladesh has a population of more than 150 million. If the seas rise three feet—quite likely to happen this century—a fifth of its land, on which some 30 million people live, will be submerged. Those 30 million will be forced to move, and when they do, it will matter how they’re regarded. As “Bangladeshis” perpetually out of place, they will likely struggle to find safe berth. It would be better, Shah suggests, to drop the labels, recognize human beings as a migratory species, and build institutions around that fact.

This is a far-reaching argument, yet when it comes to specifying what those institutions might look like, Shah has disappointingly little to say. The sole policy she endorses in her book is the UN Global Compact for Safe, Orderly and Regular Migration, a nonbinding pact that the vast majority of countries voted for in 2018. (The United States voted no.) The compact enjoins governments to ease migrants’ lives by doing things like providing them with identity documents and vocational training. But it does not abolish borders or establish anyone’s right to cross them. To the contrary, it affirms “the sovereign right of States” to “govern migration within their jurisdiction,” including “preventing irregular migration.” It’s hard to see how such an approach could suffice in an age of climate change or how it could free us from the myth of the sedentary world.

There are also deeper questions raised by the history Shah explores that go unaddressed. Racism doesn’t manifest only in border controls, which Shah discusses at length, but also in colonial conquest, removal, gentrification, and dispossession, which she says much less about. In these cases, the forces of racism combine with those of mobility, feeding off the people-don’t-belong-to-places view that Shah defends. If there is no connection between societies and land, then what can be said about English travelers founding a new society on Indigenous land in the Chesapeake Bay? Or Jewish settlers from the Soviet Union seeking a home in Palestine? Shah defends her view with gentle metaphors drawn from nature: Butterflies cross borders, so people should be allowed to do so as well. But she says less about the tendency of animals, including humans, to violently dislodge rivals upon entering new areas.

If The Next Great Migration does not resolve such issues, that is because its aim is more to trigger a conceptual shift. The world isn’t fixed in place, Shah rightly argues. People, plants, and animals move, and they do so regularly. The coming years will see more migrants than ever, and we should not see that in itself as a crisis. Migration is normal. The lemmings are all right.

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