Megafauna (eBook)

Chapter 1

“All the Hugest, and
Fiercest, and Strangest Forms Have Recently
Disappeared”

Exploring the eastern coast of Argentina in the early 1830s, in the vicinity of what is today the Puerto Belgrano Naval Base, the young Charles Darwin examined the bones of the elephant-sized ground-sloth Megatherium and at least nine other extinct species he described as “gigantic quadrupeds.”

“It is impossible,” he wrote, “to reflect on the changed state of the American continent without the deepest astonishment. Formerly it must have swarmed with great monsters: now we find mere pigmies [sic], compared with the antecedent allied races.” Darwin was astounded, too, by how recently these “great monsters” had become extinct: their bones were embedded, in some cases, in deposits containing the shells of modern, still-existing mollusk species. It was a state of affairs that cried out for an explanation. “Did man,” Darwin wondered, “after his first inroad into South America, destroy, as has been suggested, the unwieldy Megatherium and the other Edentata?”

The mystery deepened when his friend and mentor Charles Lyell informed him that North America had also lost a suite of “great monsters” (which included mammoths among many other large mammal, reptile, and bird species). “The mind at first is irresistibly hurried,” Darwin wrote, “into the belief of some great catastrophe; but thus to destroy animals…in Southern Patagonia, in Brazil, on the Cordillera of Peru, in North America up to Behring’s Straits, we must shake the entire framework of the globe.”

Darwin was to learn, in the years that followed his return from the Beagle voyage, that this “earth-shaking” wave of large-animal extinctions had engulfed not only the Americas, but also Eurasia (which had seen the relatively recent loss of mammoths, mastodonts, woolly rhinoceroses, giant deer and many other species) and Australia (where a rhino-sized marsupial herbivore, a marsupial “lion” approaching the “real” or placental lion in size, and a great many other big marsupials, reptiles and birds also disappeared near the end of the Pleistocene Epoch).

Alfred Russel Wallace, the co-discoverer with Darwin of evolution by natural selection, was equally puzzled by this recent disappearance of so many of the earth’s big land-animals, writing, in 1876, that

…we live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared; and it is, no doubt, a much better world for us now that they have gone. Yet it is a marvelous fact, and one that has hardly been sufficiently dwelt upon, this sudden dying out of so many large Mammalia, not in one place, but over half the land surface of the globe.

At first, Wallace thought that the “sudden dying out” of these big beasts had been caused by “the great and recent physical change known as the ‘Glacial Epoch’,” but, writing in 1911, his eighty-eighth year, he changed his mind:

Looking at the whole subject again, with the much larger body of facts at our command, I am convinced that the rapidity of the extinction of so many large Mammalia is actually due to man’s agency, acting in co-operation with those natural causes which at the culmination of each geological era has lead to the extinction of the larger, the most specialized, or the most strangely modified forms.

In our time, many students of this recently extinct megafauna have come to agree that the big beasts were victims of a human-inflicted overkill. Others still refuse, however, to accept this conclusion, speculating that the big animals in question may have been killed off by non-human factors such as climate change and disease. I’ll try to explain, in the chapters that follow, why I ally myself with people like the paleoecologist John Alroy who believe that the “humans did it” conclusion has long since “been ‘proven’ as thoroughly as any historical hypothesis can be”:

All of the key evidence was available years ago, and all of it firmly refutes competing, ecologically oriented hypotheses. The event’s timing, rapidity, selectivity, and geographic pattern all make good sense according to the anthropogenic model, and no sense at all otherwise. To my eyes, this assessment is so clear-cut that further “tests” are not really necessary.

***

Humans did not stop wiping out other species after they completed their settlement of the planet’s habitable continents some 12,000 years ago. The number of extinctions caused by our species increased, on the contrary, as we discovered and occupied the earth’s previously uninhabited islands. The more accessible of those islands, such as those in the Mediterranean and Caribbean seas, were reached between 10,000 and 5,000 years ago. After they had been occupied by our species, the Mediterranean islands lost a fauna which included several species of dwarf elephants, as well as dwarf mammoth, hippo and deer species, giant dormice, giant eagles, the Majorcan “goat antelope,” and a variety of giant tortoise species. After humans reached the Caribbean islands between 6,000 and 3,000 years before the present, those islands also lost giant tortoises, as well as dwarf ground sloths, endemic monkeys, bear-sized rodents, and owl species in a range of sizes characterized by Jared Diamond as “normal, giant, colossal, and titanic.”

Humans only completed the task of discovering the planet’s more remote islands in the eighteenth century, and the settlement of almost every newly discovered island group appears to have been followed by extinctions. The work of Helen James and Storrs Olson has shown, for instance, that, after Polynesian seafarers reached Hawaii around the beginning of the Common Era, they definitely exterminated thirty-five bird species, and probably exterminated fifty-five in total. After reaching the world’s fourth-largest island, Madagascar, at a time calculated to be somewhere between 920 CE and 670 CE, Indonesian seafarers had wiped out, by approximately the end of the fourteenth century, the island’s gorilla-sized lemurs and the world’s largest bird, Aepyornis, among a great many other mammals, birds and reptiles. When Polynesians reached New Zealand in the late thirteenth or fourteenth century, it took them only about a hundred years to exterminate the islands’ avian megafauna, which included 500-pound, ten-feet-tall flightless moas and the world’s largest eagle, as well as many other large and mostly flightless bird species, while the rats that had accompanied the human settlers multiplied explosively, and killed off an enormous “minifauna” of endemic frogs, flightless songbirds, ground-dwelling bats and large insect species.

As the dodos and their relatives, solitaires, were disappearing during the seventeenth and eighteenth centuries from one of the last-to-be-discovered island groups, the Mascarenes, (along with the endemic pigeons, ibises, rails, owls and some of the giant tortoise species that shared those Western Indian Ocean islands with them), humans were still exterminating big animals on or near the continental land masses. In 1627, the last aurochs, the ancestor of domesticated cattle, was killed in the Jaktoróv Forest in what is today Poland’s Warsaw Province, and in 1768—on the eve of both the industrial and the American revolutions—hunters from Kamchatka wiped out Hydrodamalis gigas, an elephant-sized dugong discovered by Vitus Bering’s expedition just twenty-seven years earlier around the previously undiscovered Komandorski Islands in the Bering Strait.

In the two-and-a-half centuries that have elapsed since this giant dugong’s disappearance, literally hundreds of vertebrate species have followed it into extinction. Nineteenth-century losses of life-forms “charismatic” enough to be noticed by our species included the bloubok antelope, the partially-striped quagga zebra, a Falkland Islands canid, and the great auk. In the twentieth century, extinctions of conspicuous species included the passenger pigeon, the earth’s two biggest woodpecker species, two Australian wallaby species, the Caribbean monk seal, and the Tasmanian marsupial “wolf.” “Charismatic” or “conspicuous” species wiped out so far in the twenty-first century include the Yangtze dolphin, the six-meter Chinese paddlefish and the 500-pound Yangtze giant turtle. Other large animals are poised to follow. The northern white rhinoceros is represented by only two females as I write this in 2021, while the Javan and Sumatran rhino species have, like many other species, declined to critically endangered levels.

As the population of our species doubled between 1973 and 2021, the process of human-caused extinction intensified. According to the WWF’s 2020 Living Planet Report, the populations of wild vertebrates (i.e., mammals, birds, fishes, reptiles and amphibians) declined, on average, by a shocking 60 percent between 1970 and 2016. “If there was a 60 percent decline in the human population,” wrote Mike Barrett, executive director of science and conservation at WWF, “that would be equivalent to emptying North America, South America, Africa, Europe, China and Oceania. That is the scale of what we have done.”

Species other than vertebrates are also suffering steep declines: insect populations in many parts of the earth have been seriously diminished. Invertebrate species represent more than 99 percent of animal diversity, but they don’t get their proportionate share of either popular or scientific attention. Non-marine mollusks (clams, mussels,...