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.
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.
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.)
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