The Sixth Extinction Book Summary

The current rate of species extinction is estimated to be 100 to 1000 times higher than the background extinction rate, which is about 0.1 extinctions per million species per year. Amphibians have been hit especially hard, with an extinction rate as much as 45,000 times the background rate. This means we are likely in the midst of the sixth mass extinction in Earth's history, this time primarily caused by human activities. Species are disappearing so fast that biologists feel they are "running through a museum and knowing that the collection's on fire."

Section: 1, Chapter: 1

In revolutionary France, naturalist Georges Cuvier studied fossilized elephant and mastodon bones, including specimens discovered in North America. He recognized that their anatomy was distinct from living species. This led him to propose that some species had gone extinct - a radical idea at the time. He identified the mastodon, mammoth, giant ground sloth, and more as "lost species." Cuvier envisioned a pre-human world populated by unfamiliar creatures that had been wiped out by sudden catastrophes.

His work established extinction as a scientific fact and the existence of a "former world" before humans, though his catastrophist views were later overturned.

Section: 1, Chapter: 2

Darwin recognized some species went extinct suddenly, like the great auk and ammonites. But wedded to Lyell's gradualism, he argued the apparent abruptness merely reflected gaps in the fossil record. Extinctions actually occurred slowly, through competition in the "struggle for existence."

However, as evidence of human-caused extinctions accumulated, a paradox emerged. How could humans overturn the "natural" pace of extinction? It implied either 1) people were unbound by nature's laws, having a "special status," or 2) catastrophic extinctions did occur, meaning Cuvier was right. Darwin sidestepped this problematic conclusion, even as he chronicled human-caused extinctions like the Charles Island tortoise.

Section: 1, Chapter: 3

Witnessing the great auk's extinction spurred ornithologist Alfred Newton to action. He realized that many seabird populations were being decimated by hunting, especially during breeding season when the birds were most vulnerable.

Newton argued: "The bird that is shot is a parent. We take advantage of its most sacred instincts to waylay it, and in depriving the parent of life, we doom the helpless offspring to the most miserable of deaths, that by hunger." In response, Newton lobbied for legal protection.

His efforts led to one of the first wildlife protection laws, the Act for the Preservation of Sea Birds in 1869. This underscores the importance of

1. studying species declines,
2. determining the anthropogenic threats, and
3. pushing for policy solutions. Individuals who experience biodiversity loss firsthand can be powerful advocates for conservation.

Section: 1, Chapter: 3

Ammonites, a group of marine mollusks, inhabited the seas for over 300 million years. They survived several mass extinctions, but finally succumbed during the End-Cretaceous event 66 million years ago. Ammonites came in a dizzying array of shapes and sizes, from tiny species to 6-foot giants.

They were abundant, diverse, and highly successful - until they rather abruptly disappeared from the fossil record. Their sudden decline, coinciding with the extinction of the dinosaurs, belies the notion that mass extinctions unfold gradually. Instead, they demonstrate that long-thriving groups can be rapidly eliminated when conditions change faster than they can adapt.

Section: 1, Chapter: 4