Saturday, September 7, 2013
Coursera: A Brief History of Humankind
by Dr. Yuval Noah Harari
Personal Lecture Notes from Lesson #4: The Human Flood
(These are personal summaries and paraphrasings of some of the major points of the lectures that I felt to be important. They are not meant to be comprehensive records nor intended to be reproductions of copyright materials. I encourage you to participate in the course for better understanding.)
Homo sapiens reached Australia about 45,000 years ago, by crossing vast stretches of open sea up to 100-150 kilometres between the islands of Indonesia and Australia. Most likely this was preceded by the establishment of first sea-faring societies in Indonesia. The journey itself is not the only fact of significance; it was the first time any species has managed to migrate out of the Afro-Asian ecological system to settle and adapt into a completely new ecological system.
The moment humans landed on the shore of Australia, they began to transform the Australian ecological system. There were all sorts of giant animals (giant kangroos, giant kaolas, giant birds, marsupial lions, the Diprotodon etc) but within a few thousand years all these animals had vanished. How did humans cause this immense change in the history of ecology of Australia?
Large animals breed slowly. Even if humans killed one Diprotodon every few months, it would've been enough to upset the balance. Humans were expert in use of fire agriculture. They burned down vast areas of dense forests, paving the way for open grasslands in which they could more easily hunt. (Eucalyptus trees are more resistant to fire; they were previously rare in Australia, and become abundant afterwards.)
Climate change also played a significant role. Under normal circumstances, Australian ecosystem could have recovered from the climate change, but the human invasion prevented it from doing so. Climate change by itself would not have been enough to cause the mass extinction.
This ecological disaster in Australia is the 'first big thing' our species accomplished in the world.
Humans reached America about 16000 years ago, or 14000 BC, in pursuit of game animals via a land bridge connecting North-Eastern Siberia with North-Western Alaska due to low sea levels. By 10,000 BC they had settled in the southern most parts of American continents, adapting to a huge variety of radically different habitats. Similar to Australia, there were many unique species of giant animals (mammoths, mastodons, saber-tooth tigers, etc). Soon after human invasion, most of these species disappeared.
Human invasion of the world is one of biggest and swiftest ecological disasters to ever befall the animal kingdom. Large terrestrial animals suffered the most. Even before the agricultural revolution, half of all the genera of large terrestrial animals had gone extinct. This was the first wave of extinction.
The second wave of extinction was re-staged in miniature versions countless time during agricultural revolution. For instance, in Madagascar there was many very unique animals, such as flightless elephant birds and giant lemurs, all of whom had vanished by 500 AD, when humans arrived to Madagascar.
Third wave of extinction is going on today, due to the industrial revolution. In prior waves, large animals of ocean had suffered little, but now many of those species are also on the brink of extinction, due to pollution and over-use of ocean resources by humans.
Dr Harari makes an apt reference to the biblical story of flood at the end. Bible tells us of the flood in which Noah built an ark and saved a pair of each animal specie to prevent their extinction. The truth is entirely different: we are the biblical flood, and the only animals we took in the ark are the few animals we needed for our purposes. The rest we condemned to destruction.