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The Sixth Extinction

An Unnatural History

By Elizabeth Kolbert
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The Sixth Extinction by Elizabeth Kolbert

The Sixth Extinction (2014) chronicles the history of species extinction and shows how humans have had more than a hand in the rapidly decreasing numbers of animal species on earth. Through industrialization and deforestation, not to mention climate change, humans have damaged the environment and disrupted habitats, leading to a massive reduction in biodiversity.

Key idea 1 of 6

How we live and how we travel the globe has directly resulted in animal species extinction.

Right now, many species of animal are endangered. Certain animals are threatened with extinction.

Yet have you ever considered how exactly a species disappears from the earth?

Historically, extinctions are rare and occur very slowly. Yet there have been periods of environmental change that have triggered mass extinctions, in which many species die in a shortened time period.

So while the “normal” rate of extinction – the background extinction rate – is generally slow, it does vary by animal group.

For instance, according to the background extinction rate for mammals, we should expect to see one species die out every 700 years. But during periods of mass extinction, this rate spikes. So far, we’re aware of five such episodes that the scientific community calls the “big five.” The extinction of dinosaurs roughly 64 million years ago, for example, was one of these five.

But mass extinctions aren’t just limited to prehistoric times. In fact, we might be experiencing one right now. We know this by looking at the actual rate of species extinction.

Take amphibians, one of the most endangered classes of animals. The actual rate of extinction today for amphibians is estimated to be 45,000 times higher than the background rate!

So the question is: What’s responsible for this disaster?

We are, actually. Humans are both directly and indirectly responsible for species extinction.

Consider modern transportation networks. Ships, planes and trains crisscross the globe, bridging continents and indirectly causing mass extinctions by introducing new organisms into environments where they can wreak havoc on existing species populations.

Panamanian golden frogs, for example, now struggle against a deadly fungus that likely came to Central America from Europe. But other species such as the great auk have been directly wiped out by hunters as well as by changes made to its habitat.

So we’re to blame for this mess. But could we have known what a profound effect our actions would have on the environment? To learn more, let’s dig into the history of evolution and extinction.

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