Once and Future Giants: What Ice Age Extinctions Tell Us About the Fate of Earth's Largest Animals

  • Sharon Levy
Oxford University Press: 2011. 280 pp. $24.95 9780195370126 | ISBN: 978-0-1953-7012-6

It puzzles me that the many large, now extinct mammals of the Pleistocene Epoch have nowhere near the legions of fans claimed by dinosaurs. Mammals win the popularity contests among existing animals, yet few children can rattle off the weights and dietary habits of the gargantuan North American ground sloth Megalonyx jeffersonii or Australia's massive buck-toothed marsupial Diprotodon optatum. Stegosaurus gets all the love.

Giant ground sloths went extinct some 10,000 years ago, but could provide conservation lessons for today. Credit: MARK HALLETT PALEOART/SPL

One fanciful explanation is that we have an abiding guilt for having killed them all off in our spear-hurling days. And it seems likely that human hunting played some part in many of these extinctions. In Once and Future Giants, biologist and journalist Sharon Levy lays out the evidence for this theory — and explores what this species drain can teach us now. The patterns and consequences of the Pleistocene die-offs can help us to predict how landscapes will change if we lose big mammals, and help us to spot warning signs of impending extinctions.

As we hesitantly take collective responsibility for these extinctions, we feel their loss more keenly. Today's 'wild' has diminished along with the megafauna. Spend enough time studying mastodons and moa, and even our most rugged landscapes begin to look tame and denuded. North America's wolves and grizzlies no longer thrill; Yellowstone Park looks like a petting zoo. “We live in a highly abnormal world,” writes Levy, quoting US palaeoecologist David Burney. “We think of ground sloths and saber-toothed cats as peculiar and foreign, but it is the world of our own ancestry, the world our species evolved in.”

So, scientists and conservationists who can easily envision the landscapes of 13,000 years ago, just before the late Pleistocene extinctions, find themselves yearning for the past. They are starting to experiment with restoring these landscapes by introducing surrogates to fill long-vacant ecological roles — to graze, to browse, to kill, to knock over trees, even to terrify.

Levy recounts various rewilding experiments. Some have been intentional, such as the Pleistocene Park nature reserve in northeastern Siberia, where rare native Yakutian horses roam. Others were accidental, such as the wild-mustang preserves of the American West. She reports on recent research supporting the notion that large animals are more than simply appealing — they can be major engineers of their ecosystems. Big predators such as the wolves of Yellowstone prevent herbivores from munching plant populations into oblivion and keep a lid on smaller predators. Big herbivores like the musk oxen of Greenland stop forests and weeds from overrunning the earth. They fertilize with their dung, and turn the earth with their big hooves.

Levy notes that many of the surrogates that conservationists use are the domesticated descendants of wild creatures. Specially bred cattle are used as proxies for extinct aurochs, the giant wild cattle that once roamed Europe, but Levy says that the modern cattle pale in comparison. Real aurochs — the kind painted by our ancestors in caves — were “longer of leg, bigger of brain, more graceful and fearless than their domesticated brethren”, she speculates.

The slightly mournful lesson of the book is this: any large animals we add to landscapes must be carefully managed. For example, condors reintroduced in the United States wear radio collars; wild mustangs are rounded up by the US government, dividing family groups and leaving excess animals held in pens. What differentiates such animals from pets?

To be truly wild, according to Levy, animals must have their numbers controlled by wild predators, not by humans. They must also live with fear. “The threat of a hungry carnivore lurking at the water hole is the essence of the truly wild horse,” she writes. And yet the idea of reintroducing predators — the key to wildness — is the most difficult to sell to local peoples around the world. Conservationists might love the thought of introducing African lions to the Great Plains in a bid to fill the gap left by the extinct American lion, but ranchers and rural residents understandably have qualms.

“We cannot raise the auroch, but its tamed descendent may yet fill a vital ecological niche,” concludes Levy in her examination of the increasing use of domestic cattle in conservation projects. Where once there were mammoths clashing tusks, giant short-faced kangaroos and woolly rhinoceroses, we now have Bessie the cow, grazing and fertilizing the soil and raising her head in vague interest as cars whizz past. It is one way of plugging the megafauna gap, but I long for the grandeur and strangeness of those lost giants.