A colt can trot shortly after birth a kitten leaves its mother to forage on its own when it is just a few weeks old. And, indeed, compared to other animals, humans are born prematurely, when many of their vital systems are still under-developed. Natural selection consequently favoured earlier births.

Women who gave birth earlier, when the infant’s brain and head were still relatively small and supple, fared better and lived to have more children. Death in childbirth became a major hazard for human females. Secondly, their muscles atrophied.Īn upright gait required narrower hips, constricting the birth canal – and this just when babies’ heads were getting bigger and bigger. Firstly, they spent more time in search of food. In Homo sapiens, the brain accounts for about 2–3 per cent of total body weight, but it consumes 25 per cent of the body’s energy when the body is at rest.Īrchaic humans paid for their large brains in two ways. Modern Sapiens sport a brain averaging 73–85 cubic inches. The earliest men and women, 2.5 million years ago, had brains of about 36 cubic inches. Mammals weighing 130 pounds have an average brain size of 12 cubic inches. It’s our current exclusivity, not that multi-species past, that is peculiar – and perhaps incriminating. The earth of a hundred millennia ago was walked by at least six different species of man. Today there are many species of foxes, bears and pigs. They were nevertheless able to produce stone tools, and even managed occasionally to hunt down some of the island’s elephants – though, to be fair, the elephants were a dwarf species as well.

This unique species, known by scientists as Homo floresiensis, reached a maximum height of only 3.5 feet and weighed no more than fifty-five pounds. Over the generations, the people of Flores became dwarves. One became the ancestor of all chimpanzees, the other is our own grandmother. Just 6 million years ago, a single female ape had two daughters. The most important thing to know about prehistoric humans is that they were insignificant animals with no more impact on their environment than gorillas, fireflies or jellyfish. This book tells the story of how these three revolutions have affected humans and their fellow organisms. The Scientific Revolution, which got under way only 500 years ago, may well end history and start something completely different.

The Agricultural Revolution sped it up about 12,000 years ago. Three important revolutions shaped the course of history: the Cognitive Revolution kick-started history about 70,000 years ago.

Sapiens by Yuval Noah Harari