Sixth Extinction

“There is grandeur in this view of life,” concludes Charles Darwin in his opus “On the Origin of Species.” “… From so simple a beginning, endless forms most beautiful and most wonderful have been, and are being evolved.” Darwin was right about many things, including the mechanism by which the plenitude of life we know as biodiversity came to thrive on this planet. Unfortunately for us, his picture of a continuously rich congregation of interacting species has hit a big roadblock.

New Yorker staff writer Elizabeth Kolbert lays out the situation in “The Sixth Extinction: An Unnatural History.” The activities of Homo sapiens – that’s right, us – are reducing the volume and kinds of other life-forms on the planet at a rate and magnitude that earn our moment in time its own epochal designation. By 2016, it is expected that the inherently conservative Geological Society of London will make it official: We’re living in an Anthropocene of our own devising.

In her elegant and quickly paced book, Kolbert reviews the history of the very concept of extinction, noting that neither Aristotle nor Pliny nor Linnaeus ever guessed there had been life-forms on Earth that no longer exist.

Georges Cuvier, the French naturalist who once compared notes on mastodon teeth with Thomas Jefferson, concluded that a variety of unearthed gigantic skeletal remains belonged to a “primitive earth,” and that a succession of catastrophes had caused these former realities to disappear.

With a significant assist from Charles Lyell, who posited that slow geological processes had created the present landscape, Darwin himself helped establish extinction as a fundamental factor in shaping life. His theory of evolution by natural selection pointed to a branching system of new life-forms made possible in part by the exiting of some older ones.

Kolbert’s riveting narrative follows the excitement, the controversies and the long slogs by which theories about how extinction operates have come to be widely accepted.

“What is sometimes labeled neocatastrophism,” she writes, “but is mostly nowadays just regarded as standard geology holds that conditions of life change only very slowly, except when they don’t.” There is slow extinction and there is fast extinction, as with the asteroid event first proposed by UC Berkeley geologist Walter Alvarez to explain the initiating cause of death at the end of the Cretaceous, one of the five major extinctions that have outlined Earth history. Today, Alvarez notes an even more mind-boggling cause for massive loss of life. “We’re seeing right now that a mass extinction can be caused by human beings.”

How do we add this up, how does science today make this claim? “It is estimated that one-third of all reef-building corals, a third of all fresh-water mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds are headed toward oblivion.”

Getting into the details, Kolbert takes her reader on a tour of extinctions around the globe. She covers ocean acidification, which gravely threatens the calcifying creatures that form a foundational part of the marine ecosystem. In the Andes, she accompanies researchers who are tracking species on the move in response to changing temperature and precipitation patterns brought on by the atmospheric effects of fossil fuel emissions. As the trees move, so shift the relationships among species who live with them. Insects and birds that pollinate and disperse seeds are becoming disconnected from the ecological alliances evolution has gradually wrought between them.

In the United States, Kolbert gingerly picks her way through carpets of bat carcasses, casualties of a runaway fungal infection. She points out that habitat fragmentation and invasive species, both the result of human alterations on the landscape, hasten the simplifying of ecosystems.

It is not possible to overstate the importance of Kolbert’s book. Her prose is lucid, accessible and even entertaining as she reveals the dark theater playing out on our globe. It is enough for one book to cover the enormous swaths of scientific territory she does here. Still, I would have liked more reference and explanation of how this accelerated take-down of creatures causes even more negative effects than the immediate one of species loss.

For example, here in North America, the loss of top predators (grizzly bears and wolves) exacerbates our current ecological woes. On the East Coast, superabundant deer are decimating forests and in some communities have to be culled by hunters. These deer also bring us proliferating ticks and Lyme disease. In the West, the lack of big teeth on the landscape actually has an impact on the water system, since the over-browsing deer and elk erode the banks of creeks and rivers, and pave the way for invasive plants to further degrade nature’s operations there.

Finally, while there is probably no hope for many of the Earth’s creatures no matter what we do right now, we certainly can stem this extinction crisis. With any hope, Kolbert’s readers will not be able to sleep until we all do our part to protect habitat for our co-travelers through what Darwin rightly called Earth’s grandeur. As climate change forces species to adjust how and where they live, we can help them by protecting enough natural places for them to do so.

This review appears in The San Francisco Chronicle Book Review, February 9, 2014.