Adapted from Chapter 5 of The Last Animal: Human History and the Fate of Life on Earth From the Ice Age to the Sixth Extinction (Princeton University Press).

Blame the word wizardry of Charles Dickens. In 1852 the great Victorian novelist described a long-forgotten naval admiral with the coinage “as dead as the Dodo.” The phrase was catchy. It appeared just a few years before Darwin’s On the Origin of Species, which stoked almost as much interest in the ends of species as in their beginnings. The poor dodo then appeared, as a clownish figure, in Alice’s Adventures in Wonderland (1865). The bird’s reputation was sealed, and the dodo became not just an emblem of extinction but a byword for doomed obsolescence. To go the way of the dodo meant to succumb to inevitable oblivion.

In truth, the dodo’s fame is out of proportion to its significance. And yet the bird, rightly understood, is the perfect allegory for the fate of island biota in modern times. That is to say, if we understand its story correctly in place and time, the precise way that its evolutionary history intersects our own, the dodo can help us understand the true depth of human impact — and why the conventional ways we measure that impact threaten to understate the damage we have done.

The dodo (Raphus cucullatus) lived on the island of Mauritius in the Mascarene archipelago in the Indian Ocean. The species was a flightless member of the pigeon/dove family (Columbidae). Dodos boasted long and colorful beaks. They ate fruit and perhaps small crabs. The portrayal of the dodo as ridiculous or clumsy is absurdly unfair. Mauritius lacked native mammals (with the exception of one bat, now endangered), so the niches normally occupied by mammals were infilled by birds, reptiles, and even crabs. The dodo, far from a defective product of evolution, was a stroke of creative genius, executed under the severest constraints — a plump pigeon playing the part of a mammal. Until we showed up, they thrived.

The Mascarenes make a rich case study in the annals of extinction history because, as Anthony Cheke and Julian Hume have observed, “Their despoilers took good notes.” This is no accident. The Mascarenes were ground zero for some of the first environmental thinking — and activism — in recognizably modern form. Deforestation and defaunation startled European observers. Mauritius, in the words of the historian Richard Grove, acquired “a disproportionate significance in the history of European colonial environmental policy.” The phrase “dead as a dodo” was not only catchy — it had been primed for success by two centuries of awareness and angst about European impact on this exotic landscape.

Even so, the exact date of the most famous extinction is still fuzzy: The dodo was last securely observed in the 1630s, but they may have survived for a few more decades. The precise cause of their demise is also obscure — in large part because the bird suffered all the usual forces of ecological upheaval at once. Their habitat was destroyed by farms. Their eggs were eaten by invasive species. And, certainly, we hunted the dodos.

The dodo symbolizes the total biotic chaos instigated when Europeans showed up on these islands. At some point or another, more than seventeen mammals, roughly three dozen birds, over a dozen reptiles, a handful of frogs, and numerous invertebrates (among them the nasty predator known as the rosy wolf snail) were introduced. The archipelago’s new residents made their presence felt: Pigs ran rampant, rats gorged on birds and their eggs, and the crab-eating macaque, a monkey native to Southeast Asia, feasted on unwary endemic animals. The effects rippled. Since the first caravel cast its shadow on these shores, more than fifty species have vanished from the Mascarenes.

Human arrival unthreaded a unique fabric woven over incomprehensible reaches of geological time. Islands confront us with the active role of geology in evolution. Islands broadly fall into two types, oceanic and continental, with distinctive evolutionary dynamics. Oceanic islands are usually volcanic in origin (e.g., Palmyra, Hawaii, the Mascarenes), though sometimes they are created by uplift (e.g., Cyprus). Continental islands are bits of landmasses that have become stranded (e.g., the British Isles). Unlike oceanic islands, continental islands start with life, a random sample drawn from continental flora and fauna, like a handful of trail mix grabbed in the dark.

Evolution will work with whatever it is given, and since the constraints are heavy, island biogeography is, in the words of David Quammen, “a catalogue of quirks and superlatives.” Physical barriers drive evolutionary divergence; island populations, separated from the continents, follow unique evolutionary paths. With predators absent and competition sparse, natural selection tilts in unexpected directions. Traits that make no sense on continents — like flightlessness in birds — flourish. Entire systems of interdependence evolve around these peculiarities. And the result is that a staggering share of the world’s species diversity has been hatched on islands.

With great distinctness comes great fragility. Small populations on islands are always vulnerable to shocks, and island species often lack defenses that continental animals must acquire in constant competition against predators, parasites, and even disease. In sum, it is exactly that which makes islands different that leaves them especially vulnerable to us. Their essence is isolation; ours is connectivity. Their tempo is Earth time; our schedules are manic. And when the two collide, the result is often catastrophic.

The Portuguese first set foot on Mauritius around 1507 CE. This timing is of enormous consequence. The year 1500 has come to denote a stark boundary in the literature on the Sixth Extinction (in essence, because the IUCN started noting known extinctions since that date in its Red List). In order to compare past and present rates of extinction, it is commonplace to start tallying species that have disappeared since that time. Round numbers are always suspect, but this one is unusually complicated. Scientists, with a solemn duty to measure things precisely, must start somewhere. Historians, whose tapestry is woven of countless threads, prefer to linger over complexity, to insist on a mix of continuity and change in all human affairs. As a scholar of divided loyalties, I can sympathize with, and become frustrated by, both sides.

Even if the year 1500 is asked to bear an unrealistic amount of weight, the choice is not arbitrary. Around this time, Europeans started crossing oceans with some regularity. The pace of change accelerated. The human impact on biodiversity not only became more pronounced in the Age of Discovery, but the record of our impact also became much richer. No one denies that something dramatically changes around the year 1500, but as the ecologist Robert Whittaker put it, “Using a baseline of AD 1500 is to begin in the middle of the movie.” Whittaker describes our impact on islands in terms of “successive waves of transformation, a form of anthropogenic ratchet effect.”

Human impact on island fauna goes back to the original Ice Age dispersal of humans. Since the Pleistocene, colonization has often meant the onset of hunting and the beginning of the end for large animals, like the pygmy hippos and dwarf elephants on Cyprus. In general, the bigger the animal and the higher up the food web, the more likely it was to vanish. Flightless birds and big reptiles bore the brunt. The giant ground birds of New Zealand, the moas, are a striking case. Geology destined it to be a land of birds. With no mammals (apart from a few bats), the avian fauna of New Zealand gives us a sense of what evolution might have done if the asteroid had wiped out the mammals. The Polynesians who arrived found an Edenic landscape: nine moa species, some towering up to 12 feet tall and weighing hundreds of pounds. Tens to hundreds of thousands of these birds roamed the islands. Within two or three centuries, every species of moa was extinct.

European colonization in the Age of Discovery marked a new era within this much longer story. What makes this period stand out is that the fate of island biodiversity became entangled with novel power dynamics between human societies. Virgin islands like Mauritius were long since rare by 1500 CE, so in most cases, Europeans arrived on already-inhabited islands, disrupting socioecological balances of long standing. The Caribbean offers a quintessential case. Even before European contact, human impact unfolded in distinct waves, but the arrival of Columbus brought a cascade of new pressures: invasive animals, unfamiliar pathogens, and extractive technologies. Indigenous societies and island ecosystems were thrown into turmoil.

The result is measured in rapid faunal turnover. In the Greater Antilles (Cuba, Hispaniola, Jamaica, and Puerto Rico), there were 116 species of mammals at the beginning of the Holocene. Around 60 of them are gone. If bats are excluded, more than 4 out of every 5 mammals have gone extinct. Cuba, which includes the largest island in the Caribbean plus an archipelago of more than three thousand small islands, has seen approximately 24 of its 59 native mammals go extinct. Deforestation and direct exploitation were important drivers, but the role of invasive species was primary: Over 40 nonnative mammals have been introduced. To the east, on Hispaniola, virtually all the nonflying mammals are gone. On Puerto Rico, all seven are gone.

Mammals were not the only victims. Caribbean birds were threatened by new predators like rats and cats, and they were evicted from their shrinking forests. More than 60 species of birds have certainly gone extinct, and most that remain are threatened or endangered. Over half of the endemic parrots of the Caribbean have been snuffed out. Reptiles have suffered a similar fate. Although modern research has skewed away from our cold-blooded cousins, reptiles are integral to Caribbean ecosystems. Yet since European arrival, turtles, snakes, and lizards have been in freefall. On Guadeloupe, for instance, half to two-thirds of snakes and lizards have gone extinct. Many of the ecological jobs undertaken by reptiles go unreplaced, making the loss of functional diversity even greater.

The story of island biodiversity will thread through future chapters too. As steam replaced sail, the problem of invasive species only became more acute. In the last century, pollution and climate change have become new threats. There was a long pre-history to human impact before 1500 CE; European colonization marks not a beginning but a distinct new phase, a speeding up; and now the Anthropocene is somehow accelerating human impact again.

All in all, the human-dominated planet leaves less life on islands. What endures is quieter, more uniform, less exuberant than before. The raw numbers are revealing. Consider that since the beginning of the late Pleistocene — roughly 126,000 years ago — about 600 bird species are known to have gone extinct, and the real number is probably twice as high. Around 80% of the extinct species were island endemics. Even more generally, around three out of every four anthropogenic extinctions to date have involved island species. If global biodiversity is a great library, written over tens of millions of years, then we have erased an inordinate portion of its rare books collection — the most archaic, most colorful, and most singular volumes.

The year 1500 always saw a speeding up of human impact on ocean life, but the contrast between oceans and islands puts the proposition of the Sixth Extinction, its limits and its strengths, in a distinct light. Oceans are vast and resilient. Islands are small and fragile. If we measure human impact by counting extinctions alone, we will underestimate what we have done to life in the oceans. At the same time, extinction is a reasonable measure of our impact on islands, at least so far, even if we rarely count or even consider the losses before 1500 CE. And counting extinctions is only one crude measure of what we care about. Conceivably, the rate of island extinction could slow down, only because we have already done so much damage to the most vulnerable ecosystems. This is hardly cause for complacency. In fact, just the opposite: Because we have already lost so much diversity on islands, we might strain all the more to protect what remains.

Previously in The Revelator:

For Bald Eagles, the Descendants of the Destroyers Became the Restorers

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