The Flood.

By Yuval Noah Harari

Prior to the Cognitive Revolution, humans of all species lived exclusively on the Afro-Asian landmass. True they had settled a few islands by swimming short stretches of water or crossing them on improvised rafts. Flores, for example, was colonized as far as back as 850,000 years ago. Yet they were unable to venture into the open sea, and, and none reached America, Australia, or remote islands such as Madagascar, New Zealand and Hawaii.

The sea barrier prevented not just humans but also many other Afro-Asian animals and plants from reaching this 'Outer World'. As a result, the organisms of distant lands like Australia and Madagascar evolved in isolation for millions upon millions of years, taking on shapes and natures very different from those of their distant Afro-Asian relatives. Planet Earth was separated into several distinct ecosystems, each made up of a unique assembly of animals and plants. Homo sapiens was about to put an end to this biological exuberance.

Following the Cognitive Revolution, Sapiens acquired the technology, the organisational skills and perhaps even the vision necessary to break out of Afro-Asian and settle in the Outer World. Their first achievement was the colonization of Australia some 45,000 years ago. Experts are hard-pressed to explain this feat. To reach Australia, humans had to cross several sea channels, some more than a hundred kilometres wide, and upon arrival, they had to adapt nearly overnight to a completely new ecosystem.

The most reasonable theory suggests that, about 45,000 years ago, the Sapiens living in the Indonesian archipelago (a group of islands separated from Asia and from each other by only narrow straits) developed the first seafaring societies. They learned how to build and manoeuvre ocean-going vessels and became long-distance fishermen, traders and explorers. This would have brought about an unprecedented transformation in human capabilities and lifestyles. Every other mammal that went to sea - seals, sea cows, dolphins - had to evolve for aeons to develop specialised organs and a hydrodynamic body. The Sapiens in Indonesia, descendants of apes who lived on the African savannah, became Pacific seafarers without growing flippers and without having to wait for their noses to migrate to the top of their heads as whales did. Instead, they built boats and learned how to steer them. And these skills enable them to reach and settle in Australia.

True, archaeologists have yet to unearth rafts, oars or fishing villages that date back as far as 45,000 years ago (they would be difficult to discover because rising sea levels have buried the ancient Indonesian shoreline under a hundred meters of ocean). Nevertheless, there is strong circumstantial evidence to support this theory, especially the fact that in the thousands of years following the settlement of Australia, Sapiens colonised a large number of small and isolated islands to its north. Some, such as Buka and Manus, were separated from the closest land by 200 kilometres of open water. It's hard to believe that anyone could have reached and colonised Manus without sophisticated vessels and sailing skills. As mentioned earlier, there is also firm evidence for regular sea trade between some of these islands, such as New Ireland and New Britain.

The journey of the first humans to Australia is one of the most important events in history, at least as important as Columbus' journey to America or the Apollo II expedition to the moon. It was the first time any human had managed to leave the Afro-Asian ecological system - indeed, the first time any large terrestrial mammal had managed to cross from Afro-Asia to Australia. Of even greater importance was what the human pioneers did in this new world. The moment the first hunter-gatherer set foot on an Australian beach was the moment that Homo sapiens climbed to the top rung in the food chain, and because of the deadliest species ever in the 4-billion- year history of life on earth.

Up until then, humans had displayed some innovative adaptations and behaviours, but their effect on the environment had been negligible. They had demonstrated remarkable success in moving into and adjusting to various habitats, but they did so without drastically changing those habitats. The settlers of Australia, or more accurately, its conquerors, didn't just adapt. They transformed the Australian ecosystem beyond recognition.

The first human footprint on a sandy Australian beach was immediately washed away by the waves. Yet when the invaders advanced inland, they left behind a different footprint, one that would never be expunged. As they pushed on they encountered a strange universe of unknown creatures that included a 200 - kilogram, two-metre kangaroo, and a marsupial lion, as massive as a modern tiger, that was the continent's largest predator. Koalas far too big to be cuddly and cute rustled in the trees and flightless birds twice the size of ostriches sprinted on the plains. Dragon-like lizards and snakes five metres long slithered through the undergrowth. The giant diprotodon, a two-and-a half- ton wombat, roamed the forests.

Except for the birds and reptiles, all these animals were marsupials - like kangaroos, they gave birth to tiny, helpless, fetus-like young which they then nurtured with milk in abdominal pouches. Marsupial mammals were almost unknown in Africa and Asia, but in Australia, they reigned supreme.

Within a few thousand years virtually all of the giants vanished. Of the twenty-four Australian animal species weighing fifty kilograms or more, twenty-three became extinct. A large number of smaller species also disappeared. Food chains throughout the entire Australian ecosystem were broken and rearranged. It was the most important transformation of the Australian ecosystem for millions of years. Was it all the fault of Homo sapiens?