Every spring, more than 300 species of bird migrate north along traditional geographic “flyways” from their winter ranges in the Caribbean and Central and South America to their breeding grounds in the United States and Canada. One day in May, a migration hot spot near my home provided me with hard-earned glimpses of migrating thrushes, vireos, orioles and 21 species of wood warblers — the most brilliant and sought-after of the migratory celebrities of spring. My reunions with a stunning hooded warbler, a crisp but shy worm-eating warbler and the flame-throated Blackburnian warbler were the highlights of my mostly homebound week of social distancing. Migration is occurring all around us, if we have the time, dedication and luck to observe it.
Migration is also in the news. On nearly every continent, human refugees are fleeing from war, ethnic and gang violence, political oppression, famine, climate change and poverty. Their travel has instigated humanitarian support efforts, military and police actions, governmental crises, political movements, xenophobic rhetoric and massive border construction projects. Refugees are risking their lives to cross the Mediterranean Sea, the Rio Grande and the Sahara, and are being detained in fortified camps on Greek islands, Australian atolls and in Bangladeshi and Texas borderlands.
In her new book, “The Next Great Migration: The Beauty and Terror of Life on the Move,” the science journalist Sonia Shah explores the history of intellectual connections among all these migration phenomena, tackling with compassion and insight a deeply complex and challenging subject. The author of four previous books, including her prescient “Pandemic: Tracking Contagions, From Cholera to Ebola and Beyond,” which came out in 2016, Shah makes clear that her interest in migration is personal. The daughter of a couple who emigrated from India to New York, she writes that her parents’ relocation “instilled in me an acute feeling of being somehow out of place, one that’s taken nearly five decades to quell.” After enduring a lifetime of questions from fellow Americans about where she is “really” from, she aims to unpack the contributions of science in shaping our expectations about the relationship between people and places.
“The Next Great Migration” argues that a view of migration as an irregularity, disorder and disruptive force has long influenced Western culture, informing eugenic and xenophobic policies in 20th-century America, the Nazi genocide and today’s anti-immigrant political movements. She explores the history of these ideas over more than three centuries, tracing a path from the 18th-century Swedish botanist Carl Linnaeus to the contemporary American white nationalist and anti-immigration crusader John Tanton. Shah contrasts this scientific tradition with a parallel track — from the 18th-century French naturalist Comte de Buffon (though he, too, was not immune to racist beliefs) to Darwin — elaborating a view of migration as natural and positive. She concludes that contemporary human migrations are not historically exceptional, but simply a manifestation of the biology of Homo migratio.
Shah reports her story from areas of refugee crisis and migration hot spots around the globe — Greek islands; Himalayan valleys; the apartments of immigrant Eritrean families in her hometown, Baltimore; and from Cape May, N.J., where bird-watchers flock in the fall to observe migrating raptors and warblers. The connections between human and animal migrations are sometimes even stronger than Shah recognizes. In eastern Panama, Shah meets a Haitian refugee family who have hiked for six days through the roadless jungle of the Darién Gap, which connects the continents of North and South America, on their circuitous route to the United States. Every spring and fall, millions of broad-winged hawks and Swainson’s hawks migrate over this same terrain on their annual migrations from breeding grounds in forests of North America to wintering grounds in the Pampas of Argentina. Created by the plate tectonic forces uniting the Americas, the Isthmus of Panama poses a geographic bottleneck for the intercontinental migrations of humans and birds. Likewise, the Greek island of Lesbos is a layover point for both human and avian migrants crossing the Mediterranean.
The scope of Shah’s story is vast, and she has taken some scientific shortcuts along the way, including a few that undermine her argument. Biologists recognize a diversity of plant and animal movements: daily movement within a home range, annual cyclic migration, dispersal from natal origin to a place of breeding, gene flow among populations of a species, historical range expansion, species dispersal over a geographic barrier, etc. Shah lumps all of these under the concept of “migration,” which makes some of her discussion confusing. How does the African origin of so much human diversity relate to the challenges cougars face crossing highways in Los Angeles? Or to the myth of altruistic lemmings leaping into the sea to their deaths?
While I was tending to apple trees in coastal Maine in early May, I was afflicted by two dozen itchy welts on the back of my neck, caused by microscopic, urticating caterpillar hairs that drifted down my collar. The hairs came from the browntail moth, which was accidentally introduced to the East Coast more than 100 years ago. Its populations have exploded in the past several years, denuding oak and other hardwood trees and causing painful rashes to many people who venture outdoors.
Now, there are many reasons a book might make a reader feel hot under the collar, but reading Shah’s dismissal of the impact of invasive species while scratching my neck was a real trigger for me. Shah connects the intellectual history of “invasive species” ecology to contemporary anti-immigrant rhetoric and policies. Although there is evidence for this argument — Nazi gardeners, for example, championed the exclusive use of native plants — she fails to engage with the genuine ecological damage that introduced species are causing around the world. Over the last century, eastern North American forests have lost the once-dominant species of chestnut and elm to disease spread by invasive pests from Europe. Today, populations of eastern hemlocks and multiple species of ash are being rapidly destroyed by introduced insect pests from Asia. But Shah mentions chestnut blight only in passing.
Nor does her book address the enormous ecological impact that human migration has already had on the planet. The paleontologist David Steadman has estimated that human colonization of the Pacific Ocean islands between 1,000 and 5,000 years ago resulted in the extinction of approximately 2,000 species of birds — one-fifth of the world’s populations. This scale of human-mediated ecological devastation cannot be dismissed as inconsequential.
Although she doesn’t use the term, Shah effectively shows that understanding human migration is fundamentally an intersectional problem, incorporating race, ethnicity, religion, gender, class, economic inequality, politics, nationalism, colonialism and health, not to mention genetics, evolution, ecology, geography, climate, climate change and even plate tectonics. Of course, Shah could not have imagined our current plight, in which the topics of her last two books would collide spectacularly: human migration during a global pandemic. It’s proof that her work addresses issues of fundamental importance to the survival and well-being of us all.