Before the Cognitive Revolution, humans lived solely on the landmass of Afro-Asia and a few surrounding islands. They didn’t alter these environments and ecosystems dramatically. Animals on the African and Asia continents had evolved alongside humans and knew how to avoid them and hold their own.
But as humans migrated to other parts of the world, parts wholly unprepared to face the threat of human beings, this would change. This chapter looks at the ecological impact of human migration to Australia, America, and then the rest of the world.
Somehow, humans managed to cross the sea barrier after the Cognitive Revolution. No one’s really sure how, but the best theory is that Sapiens in Indonesia learned how to build boats and managed to reach Australia. Human colonization of Australia is one of the most important events in history, on par with the moon landing. It was here that Sapiens rose to the top of the food chain and became the deadliest species in Earth’s history.
Before the arrival of humans, Australia was home to many large animals that sound mythical to modern ears. They included:
In just a few thousand years, all of these animals, and many more, were gone. 23 out of the 24 animals weighing 100 or more pounds became extinct.
Some researchers blame the climate, but this is a weak argument for three reasons.
Reason #1: Australia’s climate did change 45,000 years ago, when humans came to Australia, but the climate changes all the time, and this particular change wasn’t especially dramatic. Is it a coincidence that 90% of the large animals in Australia vanished right after humans arrived? The giant diprotodon, for example, had survived at least ten ice ages before humans came.
Reason #2: Climate change usually affects land and sea creatures equally. But 45,000 years ago, when humans spent far more time on land that navigating the sea, only land animals were affected.
Reason #3: It wasn’t just Australia. Wherever humans went, they left a trail of extinction behind. For example, Sapiens only reached New Zealand about 800 years ago. Within a couple hundred years, most of the local megafauna was gone, as was 60% of local bird species. There are numerous examples like this, making Sapiens in particular “look like an ecological serial killer.”
Reason #1: Although large, these Australian species weren’t hard for humans to kill.
Large animals have long pregnancies and don’t have as many children as smaller species, so they breed slowly. Even if humans only killed a few diprotodons every year, deaths could outnumber births, causing the species’ extinction within a few thousand years.
Also, because large animals had no prior experience with humans, and because humans were small and didn’t look particularly menacing, these animals didn’t run away. They didn’t have time to evolve a fear of humans. Humans caught them off guard.
Reason #2: Humans used fire agriculture.
Humans burned dense thickets to create grasslands that were easy to navigate and attracted game. Not only did this lure animals into the vicinity to be killed, it changed the vegetation. This, in turn, impacted the animals who ate the vegetation, and the animals that ate those animals. This caused the food chain to collapse.
Reason #3: Human actions may have pushed an ecosystem weakened by climate change over the edge.
Climate change may have played a part. Large animals were vulnerable to two very different threats. Regardless, humans played a crucial role. Animals may have bounced back from climate change, but humans didn’t give them a chance.
The disaster in Australia 45,000 years ago was the first mass extinction caused by humans, but it wasn’t the largest. The next major disaster was in America, 16,000 years ago.
Sapiens were the only humans to make it to America. They came in large numbers from Siberia, when the end of an ice age revealed a land bridge between Siberia and Alaska. Sapiens likely followed large prey like reindeer and mammoths into Alaska. Both were great sources of fat and fur, and hunters thrived.
For a species that evolved in Africa, Sapiens were quick to figure out how to adapt to this cold and inhospitable land. They made snowshoes, used needles to sew layers of furs and skins into thermal clothing, and made new weapons to kill their new prey.
In just a couple thousand years, maybe less, Sapiens had adapted to ecosystems and climates as diverse as those of the eastern U.S., the Mexican desert, the Amazon basin, and the Andean mountain valleys. They did all this adapting without altering their genes.
Again, wherever humans went, they brought the powers of mass extinction with them. Animals native to North America included:
Shortly after Sapiens arrived, these species were gone. Of 47 large animal genera in North America, 34 went extinct. Of 60 large animal genera in South America, 50 went extinct. Thousands of smaller animal species also went extinct.
The pattern seen in Australia and America repeated itself all over the world. Between the Cognitive and Agricultural Revolutions, humans caused half of the world’s large beasts to go extinct. And this pattern holds beyond the Agricultural Revolution. For example, Sapiens only set foot for the first time in Madagascar 1,500 years ago. Not coincidentally, this is also the time that most of Madagascar’s large animals disappeared.
Only a few islands, like the Galapagos Islands, were spared, but only because they were so remote that humans didn’t reach them until the modern age.
The mass extinction following the Cognitive Revolution is called the First Wave Extinction. After the Agricultural Revolution came the Second Wave Extinction. We’re now experiencing the Third Wave Extinction. All three waves are caused by humans.
Unless we as a species make massive changes, whales, sharks, and dolphins will probably follow the diprotodons, ground sloths, and mammoths into the abyss.