Chapter 1
The Journey That Defines Us: Migration as the Human Constant
In a world increasingly defined by walls and borders, Sonia Shah's "The Next Great Migration" arrives as a timely challenge to our fundamental assumptions about human and animal movement. The book has quietly become a favorite among progressive policymakers and environmental scientists, with figures like Alexandria Ocasio-Cortez citing it in discussions on climate migration. Published in 2020 as nationalist movements gained momentum worldwide, this work upends centuries of scientific and cultural thinking that has portrayed migration as unnatural, dangerous, and destabilizing. Instead, Shah reveals migration as perhaps our most natural state - a biological imperative shared across species that has shaped our evolution and may be crucial for our survival in a rapidly changing world.
Chapter 2
When Movement Becomes Exodus: The Modern Migration Crisis
In the sun-baked hills of southern California, butterfly expert Spring Strahm leads Shah on a search for the elusive Edith's checkerspot butterfly. These unassuming creatures have revealed something remarkable: rather than simply perishing due to climate change, they've shifted their range northward and to higher elevations. This discovery, first documented by Camille Parmesan in her groundbreaking 1996 Nature paper, wasn't anomalous but part of a global pattern. Scientists have found that 40-70% of tracked species have altered their distribution, with terrestrial species moving nearly twenty kilometers per decade toward the poles, and marine creatures moving even faster at seventy-five kilometers per decade.
This wild exodus is happening everywhere - from parasites appearing in Alaska to red foxes spreading into Arctic territory. Even in the forbidding Himalayas, forests steadily climb upward at nineteen meters per decade, bringing entire ecosystems with them. Human migration continues alongside this wild movement - Tibetan refugees traversing mountain passes, climate refugees fleeing disasters, and economic migrants seeking opportunity.
The scale of potential human movement is staggering. By 2045, desertification in sub-Saharan Africa could displace 60 million people, with rising sea levels potentially adding 180 million more by 2100. Yet despite centuries of thinking species and people belong in fixed places - ideas that have fueled anti-migration policies and fears - emerging evidence suggests migration is fundamental to our biology and history.
For journalists like Shah, migration has long been framed as disruptive. Her own work investigated how mosquitoes carrying malaria and cholera bacteria traveling with humans triggered pandemics that reshaped empires and economies. This perspective of movement as aberrant echoed her personal experience as the child of Indian immigrants to America - perpetually feeling out of place, neither fully American nor Indian, carrying a sense of marginality even after decades in American cities.
The stories of today's migrants illustrate the perilous journeys many undertake. Ghulam Haqyar, an NGO manager from Afghanistan, fled with his family after Taliban militants murdered his colleague. They sold their home at a quarter of its value and traveled through Pakistan and Iran without documentation to reach Turkey. Their crossing to Greece nearly ended in disaster when their boat's engine died mid-journey. Though they survived, their German textbooks - carried over 2,000 miles in preparation for their new lives - were ruined by seawater, joining mountains of abandoned belongings on Lesbos's shores.
From tiny Eritrea, approximately 5,000 people flee monthly to escape the country's autocratic regime. Fourteen-year-old Mariam walked nearly 24 hours over mountains to Ethiopia, defying her mother's pleas and soldiers' shoot-to-kill orders. Another Eritrean, Sophia, left her three-year-old daughter with her parents and paid smugglers to take her to Sudan and Cairo.
Chapter 3
The Manufactured Panic: How Migration Became a Crisis
Following the end of the Cold War, mass migration emerged as a new perceived global threat. Despite migration experts knowing that movement is an unexceptional ongoing reality with complex relationships to environmental changes, national security experts continued calculating migration numbers through simplistic formulas, presuming climate disruptions would automatically trigger disruptive mass migrations.
The Syrian civil war became a flashpoint for these fears. After teenagers in drought-stricken Daraa were detained and tortured for challenging President Assad, demonstrations escalated into brutal conflict. The resulting exodus sent hundreds of thousands to neighboring countries and over a million toward Turkey en route to Europe. Simultaneously, Libya's collapse opened migration pathways through North Africa. These combined flows created what media dubbed a "migrant crisis" as over a million people crossed the Mediterranean in 2015.
This migration spectacle triggered political backlash across Europe and the United States. Voters elected Donald Trump, who campaigned on building a wall; Britain voted to leave the European Union; and anti-immigrant parties gained unprecedented power across Europe. Government agencies shifted from welcoming immigrants to "securing the homeland," with European Union head Donald Tusk explicitly telling migrants: "do not come to Europe."
To justify these stances, politicians needed to portray migrants as dangerous. In January 2016, reports emerged of women being sexually assaulted by migrants during New Year's Eve celebrations in Germany. Media outlets published inflammatory stories suggesting migrants had a "special appetite" for raping local women. Germany's Interior Ministry reported 402,000 excess crimes since admitting migrants, and stories circulated about church burnings and "no-go zones" in Sweden.
Yet when investigated, these narratives collapsed: the 402,000 "excess" crimes consisted entirely of border-crossing violations; crime rates in Germany actually reached a 30-year low by 2018; the church fire was an accidental firework incident; and Swedish police officers claimed their words had been taken out of context.
Despite unauthorized immigration declining since 2007, U.S. officials under President Trump portrayed migrants as increasingly dangerous criminals. Border Patrol reported a 70% increase in assaults against agents in 2017, with their chief testifying to Congress about a 200% year-to-date increase. When two agents were found bloodied at the bottom of a culvert in Texas, officials immediately suggested they'd been "brutally beaten" by migrants.
These claims proved equally hollow: Border Patrol had changed their counting method, multiplying each incident by the number of agents, attackers, and objects used; the agents in Texas had simply fallen down a culvert; and a high-profile rape case used to justify antimigrant policies collapsed when the victim's story fell apart.
Chapter 4
The Scientific Origins of Anti-Migration Ideology
The roots of anti-migration sentiment trace back to the 18th century Swedish taxonomist Carl Linnaeus. Born to an impoverished Lutheran minister, Linnaeus grew up examining nature along lakeside woods, believing the Creator made everything with purpose. As European explorers ventured deeper into Asia, Africa, and the New World, they returned with exaggerated tales of foreign peoples that emphasized differences rather than similarities between Europeans and non-Europeans.
Unlike earlier land travel, where human diversity appeared as gradual variations, sea voyages deposited Europeans abruptly in regions with different climates and peoples, making human diversity seem discontinuous. This preoccupation with distinctions between peoples undermined recognition of migration's role in human history.
Linnaeus, a self-described Sami expert after a failed expedition to Lapland, developed his groundbreaking taxonomy while working for the Dutch East India Company. A natural "splitter" obsessed with distinctions, he initially avoided classifying humans, writing merely "Nosce te ipsum" (know yourself). His plant classification system based on sexual organs used explicit human sexual metaphors, describing botanical "marriages," "husbands," "wives," and "harlots."
Unlike Linnaeus the splitter, French naturalist Buffon saw nature as mutable and dynamic, with only "imperceptible nuances" separating its parts. He argued all humans "derive from the same stock" regardless of appearance, noting that children of European and African parents weren't sterile like mules, proving they weren't separate species. To explain human diversity while maintaining biblical origins, he proposed a history of migration from the Garden of Eden, with physical differences emerging through adaptation to various environments.
In his definitive tenth edition of Systema Naturae, Linnaeus classified over 4,000 animals and 8,000 plants while establishing a human taxonomy that settled "differences between foreigners and Europeans once and for all." He divided Homo sapiens into subspecies with stark racial stereotypes: Europeans were "white, serious, strong" and "ruled by laws"; Asians "yellow, melancholy, greedy" and "ruled by opinion"; Americans "red, ill-tempered" and "ruled by custom"; while Africans were "black, impassive, lazy" with "thick lips" and "ruled by caprice."
Linnaeus's taxonomy proclaimed natural history's independence from church teachings, conveniently facilitating Europe's colonial interests by casting foreigners as biologically distinct. His system achieved "rapid historical triumph" over Buffon's theory of common ancestry, presenting nature in discrete units defined by biological borders, with migration playing little biological role - a framework that would fuel centuries of xenophobia and racial violence.
Chapter 5
The Deadly Hybrid: Race Science and Immigration Restriction
On the streets of early twentieth-century New York, massive migrations transformed America's demographics. Over six million African Americans fled the South following emancipation, while 27 million immigrants from Europe, Asia, the Caribbean, and Central America poured into America between 1880-1930. By 1900, immigrants and their children outnumbered native-born Americans in New York City, dismantling the cultural dominance of old elites like Henry Fairfield Osborn and Madison Grant - aristocratic "scientific men" who would soon be alarmed by what they saw as the biological implications of this demographic transformation.
Throughout the nineteenth century, scientists had elevated Linnaeus's theory of human subspecies into scientific "truth." Harvard zoologist Louis Agassiz proclaimed that "the several races of men are well marked and distinct," commissioning photographs of enslaved Africans as visual archives of "pure racial types." Race scientists developed metrics like the "cephalic index" and "sitting height index" to distinguish human subspecies, despite struggling with contradictory data.
Beyond race science, Grant and Osborn promoted new ideas about biological inheritance. While social reformers advocated for improvements in sanitation, nutrition, and education, the emerging theory of "Weismannism" suggested inherited traits passed unchanged through generations, impervious to environmental conditions. Leading eugenicists warned Americans could "rapidly become darker in pigmentation, smaller in stature, more mercurial" and "more given to crimes." Grant dramatically claimed "Miscegenation is the first step toward extinction," believing immigrants would breed superior human subspecies into oblivion.
Most Americans in the pre-WWI era accepted certain peoples were "backward and undesirable," with Congress having closed borders to Chinese immigrants and the "feeble-minded" in 1882. Yet while scientific elites warned of biological menace, popular culture embraced immigration. The Statue of Liberty welcomed the "huddled masses," settlement houses helped newcomers assimilate, and Roosevelt enthusiastically attended the 1908 musical "The Melting Pot" celebrating immigrant amalgamation.
Public attention to immigration's supposed biohazards increased as America entered WWI. Grant's 1916 book "The Passing of the Great Race" became a bestseller, with journalists warning immigration would create "a hybrid race of people as worthless and futile as the good-for-nothing mongrels of Central America." Universities embraced eugenics, with courses jumping from 44 to 376 between 1914-1928. Flawed intelligence tests administered at Ellis Island claimed to find that over 80% of Jewish, Hungarian, Italian and Russian immigrants were "feeble-minded."
Despite mounting flawed research claiming to prove immigrants' biological inferiority, evidence contradicting the catastrophic predictions of racial hybridization emerged. Studies showed mixed-race people were often more fertile, not less, as race theory predicted. Swedish physician Herman Lundborg discovered that mixed-race children of Lapps, Finns, and Swedes appeared taller, stronger and more graceful than their "pure-race" ancestors.
Nevertheless, in September 1921, scientists gathered at the American Museum of Natural History for the Second International Congress of Eugenics. Osborn opened by framing the political aim: "We are engaged in a serious struggle to maintain our historic institutions through barring the entrance to those who are unfit." After the conference, Grant, Osborn and other scientists formed an organization to translate scientific findings into policy, drafting a new immigration law that expanded and made permanent earlier temporary restrictions.
The Johnson-Reed Act severely restricted immigration, with over 80% of quotas reserved for western and northern Europeans. Immigration plummeted from 800,000 in 1921 to under 100,000 annually. Hitler, who called Grant's book "my bible," implemented his own program against "outsiders." When Jewish refugees later sought asylum from Nazi persecution, America maintained its closed borders, even rejecting a ship carrying 900 asylum seekers, many of whom later died in the Holocaust.
Chapter 6
The Myth of the Suicidal Migrant: How Science Reinforced Borders
While Grant and Osborn raised alarms about human migrants crossing borders, British scientists examined the challenges of populations constrained within borders. Charles Sutherland Elton, a young Oxford zoologist, proposed that lemmings committed mass suicide by migration as a form of population control - marching into the sea and drowning themselves when their numbers grew too large. This explanation for the mysterious "factor X" that regulated population cycles earned Elton acclaim, despite contradicting Darwin's theory of natural selection.
According to Gause's Law, developed from Russian biologist Georgii Gause's experiments with yeast in the 1930s, two species cannot share the same ecological niche - one must inevitably destroy the other. This principle became central to scientific thinking about migration, reinforcing the idea that nature was "filled up" with no room for newcomers. Scientists dismissed evidence contradicting this theory, maintaining their belief that migrants were dangerous intruders.
The conviction that drove anti-migrant ideas was rooted in a belief that nature existed in stasis, with unchanging geography where each species had established itself in its own specialized niche. This view elevated the native over the newcomer across society - from museum displays to citizenship laws based on jus soli (right of the soil). In Germany, Nazi leaders took these ideas to extremes, purging "foreign" plants from gardens and landscapes.
The scientific portrayal of migrants as "sacrificial zombies" and "malevolent intruders" succeeded largely because the true scale of migration remained obscure. All around us, remarkable journeys occur: half-gram monarch butterflies flying three thousand kilometers between North America and Mexico; bar-headed geese soaring over the Himalayas at six thousand meters; eels metamorphosing for Atlantic crossings. But scientists couldn't study migration in laboratories, and field observation was limited.
In March 1941, as London endured bombing, British radar operators detected massive formations crossing the English Channel. Fearing German invasion, the Royal Air Force scrambled fighters only to find empty skies. These mysterious "radar angels" continued appearing throughout the war. Ornithologist David Lack, who worked on radar technology during the war, proposed these were migrating birds. Military officials scoffed, believing birds couldn't fly at night or register on equipment designed for fighter jets. Years later, Lack confirmed his theory when he witnessed starlings creating the exact patterns seen on radar screens.
After the war, Charles Elton's concerns about ecological threats from migrants intensified. Using war metaphors, he warned of migrant species launching "surprise attacks" with "explosive violence" to achieve "complete domination." His hastily written 1958 book "The Ecology of Invasions by Animals and Plants" launched invasion biology, selectively focusing on disruptive species while ignoring benefits of introduced species like corn, soybeans, and wheat.
In 1958, Walt Disney's "White Wilderness" documentary cemented the lemming suicide myth through deliberate deception. The film showed lemmings supposedly committing mass suicide by leaping off cliffs into the Arctic sea - a scene completely staged by filmmakers who captured lemmings, transported them 1,000 miles to a set outside Calgary, filmed them running on turntables to simulate migration, then dumped them from trucks over a riverbank while cameras rolled. Despite this fraud, the film won the 1959 Academy Award for best documentary and was shown in schools nationwide for decades.
Chapter 7
From Ecology to Ideology: Population Control and Anti-Immigration
Scientists in the post-WWII era began warning about the ecological dangers of unchecked population growth, reviving Malthusian concerns. Unlike the mythical self-sacrificing lemmings, real ecological case studies like the Kaibab Plateau deer and St. Matthew Island reindeer demonstrated what happens when populations grow unchecked without predators: explosive growth followed by environmental destruction and population collapse.
Thomas Malthus's 18th-century warnings about population growth outstripping resources gained new attention after WWII. Though previously dismissed as "hideous blasphemy" by critics like Engels when birth rates declined with prosperity (the "demographic transition"), post-war trends challenged this optimism. The baby boom in prosperous countries and falling death rates in poorer nations without corresponding economic development revived Malthusian concerns.
Stanford biologist Paul Ehrlich, who had absorbed Malthusian warnings from earlier environmentalists, studied checkerspot butterflies whose behavior contradicted migration theories. Despite having wings, these butterflies showed a "remarkable lack of wanderlust," rarely leaving their mountain patches even when conditions deteriorated. Ehrlich's perspective changed dramatically after visiting South Asia, where human population pressures became his new concern.
Ehrlich arrived in New Delhi in June 1966 during the pre-monsoon heat and was immediately repulsed by what he saw as overpopulation. While counterculture Americans found India transformative, Ehrlich saw only disaster: "The streets seemed alive with people... People eating, washing, sleeping... People, people, people." Though he attributed these conditions to overpopulation, the crowding in Delhi actually stemmed from government programs encouraging rural migration, and Kashmir's environmental damage resulted largely from a recent India-Pakistan war.
After appearing on Johnny Carson's Tonight Show, Ehrlich became a celebrity overnight. His book "The Population Bomb" sold nearly 2 million copies by 1970's end, creating what one reader called "end-of-the-world fear." Despite protests from African American activists who accused the movement of targeting "blacks, other non-whites, the American poor and certain non-white and ethnic immigrants," the population control movement gained momentum.
By June 1975, the population control movement achieved a major victory when India's prime minister suspended the constitution and implemented a nationwide sterilization program. Men with more than three living children were required to undergo sterilization, while pregnant women with three children were forced to abort.
John Tanton, an ophthalmologist from Michigan deeply influenced by Ehrlich's book, drew misguided parallels between honeybee colonies expelling drones and human immigration policy. Though presenting himself as rational and morally upright, Tanton privately held biological determinist views, categorizing people as either "homo contraceptivus" (Europeans and Americans with smaller families) or "homo progenitiva" (immigrants with "traditionally high fertility patterns").
Tanton rose quickly through Zero Population Growth's ranks, becoming president by 1975 and redirecting the organization's focus from global birth rates to national immigration restrictions. Under his leadership, environmental organizations like the National Wildlife Federation adopted anti-immigration positions.
By the time the population control movement crashed, demographic trends had already reversed. The U.S. birth rate had been declining since 1955, falling below Zero Population Growth's recommended level by 1972. Global population growth had peaked, and demographic transition theory regained its authority. Environmental activists turned to less contentious ways to protect nature than criticizing poor people's reproductive habits.
Chapter 8
Homo Migratio: The Truth About Human Origins
The idea of migration as disruptive has shaped our understanding of human history, but recent scientific discoveries have upended centuries of thinking. While Darwin suggested human ancestors originated in Africa, how people reached remote places like Himalayan heights, Amazon depths, Arctic tundras, and Pacific islands remained mysterious until the late twentieth century.
The islands of Polynesia presented a particular migration mystery. When European explorers like James Cook reached these remote Pacific islands using advanced navigational technology, they found them already inhabited by related peoples across thousands of miles of ocean. Norwegian adventurer Thor Heyerdahl rejected the idea of purposeful migration, proposing instead that Polynesian settlers had drifted accidentally from Peru on balsa rafts. His journey on the Kon-Tiki raft became wildly popular, convincing many that ancient migrations were merely accidents rather than intentional voyages.
University of Pennsylvania anthropologist Carleton Coon went further, claiming there had been no prehistoric migrations at all. His 1962 book "The Origin of Races" argued that human races had evolved separately on different continents from Homo erectus into Homo sapiens at different rates-with Caucasoids evolving first, explaining their supposed superiority, while Black Africans were "two hundred thousand years less evolved."
The sedentary past paradigm finally began to crack in the 1960s when scientists discovered mitochondrial DNA. Population geneticist Luigi Luca Cavalli-Sforza incorporated DNA evidence with skull changes, pathogen evolution, languages, and archaeology to prove we had indeed migrated from Africa hundreds of thousands of years ago.
The Human Genome Project in 2000 revealed startling findings that challenged sedentist myths. Humans showed barely any genetic difference-just 0.1 percent variation between individuals-regardless of race or appearance. Even more surprising, we possess only about 20,000 genes, roughly the same number as a millimeter-long nematode worm, not the 100,000 scientists had expected.
The discovery that the petrous bone preserves ancient DNA revolutionized paleogenetics. While only five ancient genomes had been published by 2010, by 2017 there were over three thousand. This explosion of data revealed that human migration was far more complex than previously thought. When our ancestors left Africa, they encountered and interbred with archaic humans like Neanderthals and Denisovans who had migrated there earlier. Modern Europeans and Asians carry about 2% Neanderthal DNA, while people in New Guinea and Australia have similar proportions of Denisovan ancestry.
The image of human populations as separate branches on an evolutionary tree is fundamentally flawed. Our history more closely resembles "inosculation"-where branches merge back together after separating. Like a braided tree with branches sprouting and then reuniting, human populations have migrated, met, merged, and migrated again throughout history. Given this history of constant movement, Linnaeus's name for our species-Homo sapiens ("wise man")-might be less apt than Homo migratio.
Chapter 9
Reimagining Migration: From Crisis to Solution
The contradiction in how we view species movement is striking. Nature enthusiasts who celebrate bird migration often condemn plant movement as "invasive," despite evidence that species have been moving across borders for millennia. Rather than accept Darwin's theory of species migration, many 19th-century scientists proposed fantastical land bridges spanning thousands of miles between continents. The conflict between Linnaean sedentism and Darwinian migration remained unresolved until the 1970s, when plate tectonics provided an alternative explanation.
Since the 1960s, the U.S. government has managed national parks as sanctuaries from "alien border crossers," following recommendations to preserve ecosystems as they appeared to "the first European visitors." Books with alarming titles like "Immigrant Killers" and "Alien Invasion" warned of threats from "German" wasps and "African" snails. One biologist calculated that free movement of species would reduce land animals by 65%, land birds by 47%, and ocean life by 58%.
However, the revolution in animal tracking technology has forced ecologists to reconsider these dire predictions. Scientists like Martin Wikelski quickly discovered stunning migration patterns: Arctic terns flying 70,900 kilometers; jaguars ranging areas ten times larger than previously thought; zebras making 500-kilometer migrations; estuarine crocodiles swimming over 200 miles in ocean; and wolves trekking 1,000 kilometers across mountains and frozen rivers.
Only 10 percent of introduced species establish themselves, and only 10 percent of those become problematic-meaning just 1 percent cause significant disruption. Even maligned species like zebra mussels and purple loosestrife have been found to contribute positively to ecosystems. The classification of species as "native" or "alien" has increasingly been questioned as an organizing principle of conservation.
Biologists have determined that migration likely evolved as an adaptive response to environmental change. Hugh Dingle's formula predicts migratory behavior based on the ratio between reproduction time and environmental stability: if reproduction takes longer than habitat stability lasts, migration is likely to emerge.
Migration serves ecological functions beyond individual survival. Wild migrants build entire ecosystems by dispersing pollen and seeds - over 90% of rainforest trees depend on animal seed dispersal. Migrants also introduce genetic diversity to isolated populations, preventing inbreeding depression. Experiments show that habitats connected by migration corridors flourish with twice the biodiversity of isolated patches.
Despite being the ultimate migratory species, we lack consensus on why humans move. Some theories suggest our first migrations were accidental byproducts - like following migratory prey animals. Economic opportunity remains a powerful driver, with migrants worldwide sending over $500 billion annually to their home countries. Yet economists' attempts to reduce migration to mathematical formulas fail to capture its complexity.
Migration appears encoded in our bodies, just as in wild species. Human bodies respond dynamically to environmental changes - like developing more functional sweat glands when exposed to heat during early years. As people migrated from Africa into new environments, our bodies adapted through genetic variants that helped us survive local conditions.
Migrants aren't random populations but tend to be those with portable capital - good health, skills, education, and social connections rather than land or titles. They're typically middle-class working people, younger and better educated than peers they leave behind. The "healthy migrant effect" shows they experience lower mortality rates than host populations despite worse living conditions.
Border fortifications have proliferated worldwide, yet they rarely stop migration. Instead, they deflect it into more dangerous routes - "like squeezing a balloon. When one route closes, the flows increase on another." As safer paths close, migrants venture deeper into deserts, launch boats into rougher waters, and climb higher mountains, often hiring smugglers.
As the myth of a sedentary human past evaporates, the question emerges: not why people migrate, but why their movements inspire terror. Xenophobia doesn't uniformly correlate with the proportion of newcomers in an area or economic distress. Research shows it flourishes in relatively homogenous places experiencing rapid demographic change, where the contrast between natives and newcomers becomes conspicuous.
New conservation efforts are creating corridors across which animals can safely move, stitching together private lands, ranches, farms, and parks. Similarly, we can reimagine human borders becoming softer and more permeable, like those between U.S. states or European countries. The UN's Global Compact for Safe, Orderly and Regular Migration offers a framework for creating legal pathways, collecting data, facilitating remittances, and reducing detention.
We can continue treating migration as a crisis, or reclaim our history as migrants and transform it into a solution. After all, the wall between Mexico and the United States serves as a passageway for wildlife - bighorn sheep, mountain lions, and checkerspot butterflies - who continue to migrate northward as the climate shifts. Despite centuries of being condemned as invaders, human migrants also persist in their journeys, their slight bodies easily lifting over the walls meant to contain movement.
