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May 26, 2014
Book Review: The Sixth Extinction: an Unnatural History, by Elizabeth Kolbert
    by Robert Kropp

The New Yorker staff writer travels through space and time to assert that a mass extinction is underway, this time at the hands of human agency. Second in a two-part series.

Many of the staff writers for New Yorker magazine tend to flesh out often brilliant essays into books, either because their affiliations give them the opportunity or their subject matter begs for greater depth. In The Sixth Extinction: an Unnatural History, Elizabeth Kolbert relies on both: her contacts in many of the ecological hot spots around the globe are numerous, and her forays into the underlying science serve to underscore the gravity of the first mass extinction in our planet's history to be caused by human agency.

Beginning with the sudden and initially mysterious die-off of formerly ubiquitous golden frogs in Panama—a near-extinction brought about by the sudden proliferation of the chytrid fungus, a proliferation made possible both by rising global temperatures and the ease with which species can now become invasive—The Sixth Extinction then tours previous mass extinctions, describing how scientists from the eighteenth century onward used fossil records and other sources to determine the causes of them.

It turns out that previous mass extinctions cannot be attributed to a single cause. More than 400 million years ago, the end-Ordovician extinction occurred, an event now largely attributed to glaciation. Gaps in the coral reef record suggest that the end-Devonian extinction about one hundred million years later also occurred due to climatic changes, and the end-Permian extinction seems to have been brought about by climate changes similar to the worst-case scenarios that scientists are contemplating for our era.

Ocean acidification, which occurs when CO2 rises to previously unseen levels, contributed to both the end-Permian and end-Triassic extinctions. Then came the most famous of all the mass extinctions of the past, the end-Cretaceous, which occurred very rapidly about 66 million years ago and wiped out the dinosaurs. Eventually, it was learned that a massive asteroid measuring six miles across had struck the earth in Mexico; but as recently as the 1980s, Kolbert reports, when Walter and Luis Alvarez published a paper arguing for such a conclusion, they were roundly criticized by paleontologists.

Now we are living in the time of the sixth mass extinction, with species dying off at rates unimaginable in the normal course of evolution. “We have entered a new epoch,” Kolbert writes, “which has no analog in earth's history.” Increasingly among scientists, the epoch we are now in is being referred to as the Anthropocene; it is an era in which almost nothing about the planet escapes the effects of human activity. Climate change and the ocean acidification accompanying it are primary culprits in the extinction of species that human beings have unleashed. So too is the proliferation of invasive species, which has been made so easy by human exploration and travel that the world can now be referred to as New Pangaea. The original Pangaea was the massive continent that existed before tectonic shifts separated South America from Africa.

And then there are the more blatant actions caused by the hands and tools of human beings. Why is it, the author asks, that so many of the world's greatest mammals—from mastodons and mammoths to our close relatives the Neanderthals—died off when no concrete evidence of a concurrent mass extinction exists? The correlation unearthed by scientists reveals that each of these die offs of great mammals occurred when human beings moved into their territories. Either we hunted them down or we altered their habitats so thoroughly that they ceased to exist. (Kolbert also points out that the genetic record indicates that human beings interbred with Neanderthals before causing their demise; today's humans have as much as four percent Neanderthal DNA in their genetic code.)

“In an extinction event of our own making, what happens to us?” Kolbert asks in her concluding chapter. She lists examples of human altruism that have made some strides in undoing some of the damage we have inflicted: the banning of DDT in 1972, for example, and the passage of the Endangered Species Act in the US two years later. But she quotes the renowned anthropologist Richard Leakey as well, who warned, “Homo sapiens might not be only the agent of the sixth extinction, but also risks being one of its victims.”

“Right now, in the amazing moment that to us counts as the present, we are deciding, without quite meaning to, which evolutionary pathways will remain open and which will forever be closed,” Kolbert concludes. “No other creature has ever managed this, and it will, unfortunately, be our most enduring legacy.”

Robert Kropp can be contacted at


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