The Flood

This chapter delivers one of Harari's most unsettling arguments: long before agriculture or industry, foraging Homo sapiens were already among the most ecologically destructive species that ever lived. Wherever sapiens expanded, the landscape did not simply gain a clever ape — it lost animals that had endured ice ages and volcanic upheavals for millions of years.

The clearest case is Australia. When humans arrived roughly 45,000 years ago, the continent teemed with giant marsupials, flightless birds, and enormous reptiles. Within a few thousand years, the overwhelming majority of Australia's large animals were gone — some twenty-three of twenty-four species weighing over fifty kilograms vanished. The timing tracks the arrival of humans far too closely to be coincidence.

The Americas tell the same story. As sapiens spread south from Alaska around 16,000 years ago, a spectacular megafauna — mammoths, mastodons, giant ground sloths, saber-toothed cats, native horses and camels — disappeared in a geological blink. Island after island repeats the pattern: large, long-established species collapse soon after the first humans set foot on their shores.

Harari weighs the competing explanations — climate change at the end of the ice age, and human impact — and argues that humans were the decisive factor. The animals had no instinctive fear of the newly arrived predator, having never faced a hunter that used projectiles and coordinated tactics, so they were slow to flee and easy to kill. Foragers also reshaped whole environments through fire, using controlled burning to clear land and drive game, which transformed habitats far beyond the reach of their spears.

He frames these losses as the first of three great waves of extinction. The first wave accompanied the spread of foragers; the second came with farmers; the third is unfolding now with industrial society. Recognizing the first wave matters because it shatters a comforting myth — the idea of ecologically innocent ancestors who lived in perfect harmony with nature until civilization spoiled everything.

The evidence, Harari insists, points the other way. Stone Age humans were responsible for the extinction of about half the planet's large terrestrial mammals well before anyone planted a field or built a factory. Their small numbers and simple tools did not make them gentle; they made them slow, but no less thorough, in reshaping ecosystems to their advantage.

The applied takeaway is a corrective to how we imagine our relationship with the natural world. If we want to understand the present ecological crisis, we should not picture it as a fall from an original harmony but as the latest and largest chapter in a very old human habit. Sapiens did not become a planet-altering force with the steam engine; we have been one, in Harari's telling, since the first foragers walked into a new land.