The Sixth Extinction

Scientists estimate that the background rate of extinction—the normal, slow trickle of species disappearing over geological time—is roughly one species per million per year. Yet current estimates, even conservative ones, place today's extinction rate at 100 to 1,000 times that background level. This acceleration means we are losing dozens, if not hundreds, of species every single day. This is a present-day calculation based on observed population collapses across the globe, from amphibians vanishing from pristine rainforests to corals bleaching in warming seas. The sheer velocity of this change is unprecedented in the last 66 million years, creating a biological crisis that rivals the asteroid impact that wiped out the dinosaurs.

This alarming acceleration is what compelled journalist Elizabeth Kolbert to travel the world, investigating the front lines of this unfolding event. As a staff writer for The New Yorker, Kolbert had a knack for translating complex science into gripping narratives. She journeyed from the Great Barrier Reef to the Andes, and from a remote Icelandic island to her own backyard, speaking with the scientists who were documenting these losses firsthand. She was documenting the present—understanding how one species, our own, became a geological force capable of altering the planet's evolutionary trajectory and initiating what many now call the sixth mass extinction.

Module 1: The New Rules of the Game

For most of Earth’s history, evolution followed a certain logic. Big, slow-reproducing animals like mammoths dominated. Small, fast-breeding species filled the niches. But with the arrival of modern humans, the rules changed. Suddenly, being big and slow became a fatal liability.

Kolbert starts by showing us how human expansion consistently triggers extinction events. This is an ancient pattern. When early humans spread out of Africa and into new continents, they left a trail of disappearance. In Europe, they encountered the Neanderthals, creatures very much like themselves. Soon after, the Neanderthals were gone. In the Americas, they met giant sloths and saber-toothed cats. Those megafauna vanished. The same pattern repeated in Australia with its giant marsupials and in New Zealand with the flightless moa birds. The common denominator was us.

This leads to a crucial insight about our own nature. A key human trait is a restless drive that constantly pushes boundaries, for better or worse. Svante Pääbo, a paleogeneticist featured in the book, calls it a kind of "madness." It’s the impulse that drove our ancestors to cross open oceans without seeing land. It’s the same impulse that drives us to build global supply chains and digital networks. Neanderthals were smart and strong, but they stayed within their known world. We didn't. This restlessness is our superpower. It's also the source of our planetary-scale disruption.

And here's the thing. This disruption is now happening at an unprecedented speed. Kolbert introduces us to the concept of the Anthropocene. It's a proposed new geological epoch defined by human impact. We have become a geological force, altering the planet's fundamental systems. We move more earth and rock than all natural processes combined. We've dammed most of the world's major rivers. We've changed the chemical composition of the atmosphere and the oceans. This is a literal reality. Future geologists will be able to see our legacy—a thin, distinct layer in the rock, full of plastics, pollutants, and the fossils of extinct species.

So, what does this mean for today? It means the strategies that helped species survive for millions of years are no longer effective. The game has been rewritten. The new rules favor species that can adapt to us, or get out of our way. And for many, there's nowhere left to go.