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A provocative treatise argues that, for many species, the era of extinction may be all right

Inheritors of the Earth: How Nature Is Thriving in an Age of Extinction

Chris D. Thomas
308 pp.
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Way back at the turn of the millennium, political scientist and climate provocateur Bjorn Lomborg pointed out with some satisfaction that the island of Puerto Rico, despite very extensive deforestation and land conversion, was home to more bird species than ever before (1). Some 10 years later, a pair of high-profile studies offered a surprising generalization: On average, various sites the world over showed no net loss of species over time (2, 3).

How does this square with the fact that we are witnesses to a toll of extinction perhaps rivaling the one that decimated the dinosaurs? With the low-key, rumpled-scientist style that Brits do well, respected ecologist Chris Thomas tours the globe to help us make sense of these conflicting patterns. More controversially, he equates today’s changes with past changes to assuage us that perhaps the unprecedented impacts of humanity are, well, OK.

In some detail, Thomas illustrates how we have colonized the planet, creating habitats that we, and many other species, like. His favorite example is the house sparrow, originally confined to the steppes of Central Asia. The sparrow thrives in human habitats; you are now just as likely to feed one under a café table in San Juan as in Sevastopol.

But thus has it always been: Species come and go from place to place as circumstances and opportunities arise. The alpacas that we associate with the South American Andes are actually North American camels that invaded when the two continents joined some 3 million years ago. They crossed the Panamanian isthmus, likely propelled by changing environments.

In Thomas’s coinage, humans have transformed the planet into a “New Pangea,” both changing environments and moving species around. The endangered Monterrey pine, naturally confined to a few bits of coastal California, now thrives across four continents. Similarly, the gumtree in my local park is, in Thomas’s words, “Australia’s gift to the world.” Land conversion, active transport, and climate change are producing new opportunities for those lucky species that can grab them.

Our planet has shrunk considerably, and once-remote places increasingly resemble each other. Indeed, a sense of global contraction hangs over the entire book.

Individual habitats are often not as diverse as they could be, meaning that there is usually room for our biological chattel. This seems especially true of islands: Clear the forest, plant fields and gardens, and—though some species disappear—the ones that come compensate, leading to no net loss.

Thomas goes one large step further. In a section titled “Genesis Six,” he suggests that all this movement has also led to an increase in speciation, going so far as to suggest that the production of new land plants may be higher now than ever before.


The sparrow is one of many species thriving in human-built habitats around the world.

New species can arise when two old species meet and hybridize or when a species adapts to local conditions in a new environment. The Asian house sparrow, for example, has now interbred with a related species in Italy to produce a new bird that may eventually be considered a bona fide species; the yellow star thistle, introduced to California in 1923, already prefers not to breed with its parent from Spain. Thomas muses as to when the New World thistle will switch from the reviled invasive it is now to the treasured Californian endemic it might become.

The idea that speciation is on the rise is provocative. The amount of movement be-tween locales must be just right, and it is an open question whether humans have inadvertently produced such a Goldilocks effect.

But the book’s real controversy follows. Thomas ends by arguing that, because biodiversity change is natural and because human behavior is ultimately the product of natural selection, human-induced biodiversity gains and losses are also natural. This is a decidedly nonstandard definition of “natural,” so it will likely be met with some bewilderment. That aside, the inevitability (and pace) of global change demands the sort of fresh thinking that is found in Inheritors of the Earth. Thomas likens the earth to a new Noah’s Ark, and I agree: At this point, we are more captain and crew than passengers and stowaways.

Perhaps it is not surprising that Thomas’s writing is filled with tenderness for the Brit-ish countryside. The creatures that now call that place home, like those in Puerto Rico, have found a way to coexist with us. Such species may be all that we should reasonably expect as companions into the future. But then again, perhaps we can do better.


  1. B. Lomborg, The Skeptical Environmentalist (Cambridge Univ. Press, Cambridge, 1998).

  2. M. Vellend et al. PNAS 110, 48 (2013).

  3. M. Dornelas et al. Science 344, 296 (2014).

About the author

The reviewer is at the Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada.