I bought Once and Future Giants by Sharon Levy after seeing a review on a science blog. It is indeed an excellent book, though at times it seems that it covers almost too many topics. All, however, have one thread in common: our present ecosystems were to some extent broken by the extinction of large mammals, which can have a profound impact on their environments. Who expected, for instance, that the re-introduction of wolves to Yellowstone would have a positive impact on songbirds and possibly, if the wolves spread far enough, on antelope?

The book attracted me primarily because of the debate on whether the Pleistocene megafauna (mammoth, mastodon, saber-tooth cats, dire wolves, and ground sloths, among others) died out because of climate change or because of overkill by humans, as proposed by Paul Martin. I have Martin’s book, and have been more than half convinced by his arguments. Certainly it has seemed unlikely to me that the warming at the end of the Pleistocene was enough in itself to trigger the extinction of a large number of animals who had survived similar transitions from glacial to interglacial repeatedly in the past. In fact, if we ignore the last fifty years, all the evidence is that it was warmer than the Recent during at least some past interglacials. But Martin very definitely writes as an advocate for his theory, glossing over the problems.

Sharon Levy has written a more balanced book, and one that tends to agree more with my own conclusions. Yes, the changes in climate at the close of the last ice age undoubtedly stressed the Pleistocene megafauna. But the major difference between the last warming and the ones that had happened before was that human beings had emerged as a major predator, and one against whom the large herbivores had no natural defenses. As she points out, the Clovis people need not have killed many mammoths or ground sloths. But human predation, unlike predation by most animals, tends to target healthy animals, often pregnant females. This disrupts the natural social groupings of herbivores, already under stress from climate and habitat change. As the herbivores are killed off, the large carnivores may well die off from starvation. Some of the environmental effects brought about by humans, such as those caused by fire, may also be partly to blame.

The idea of re-wilding, of introducing either the original species (as wolves were reintroduced to Yellowstone) or a surrogate is even more controversial – but the controversies are even more political than the reintroduction of the wolf. Predators are an important part of ecosystems – but people simply do not want to live with animals capable of killing large prey. Neither do they want large herbivores, such as camels or elephants, to compete with domesticated animals for food. The mustang problem is an example of both.

A less well-known problem is certain aspects of the protection of endangered species. In some cases animals or plants stressed by the ongoing changes in climate need to be relocated closer to the poles or to higher elevations – but this is often prohibited by the very laws meant to protect them.

I’m fond of the large megafauna, and would love to see a mammoth in person. In fact the terraformed landscape of Falaron in my own novel Tourist Trap, based on ice-age North America, reflects that wishful thinking. But I have to confess I’d have my doubts about living with the creatures of the Ice Age, or with introduced African lions.

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