Notes and summary on the book "Sapiens a brief history of humankind" from Yuval Harari. Chapter 1: an animal of no significance 13.5 billion y: age of the universe 4.5 billion y: age of planet earth 3.8 billion y: organisms on earth 2.5 million y: Australopithecus. 70.000: Homo Sapiens. Three revolutions shaped history of humankind: the Cognitive revolution at -70.000, the Agricultural Revolution at -10.000 BC and the Scientific Revolution in 1500. Different species of humans have existed. Neanderthals in Europe. Home Erectus in eastern Asia. Homo Soloensis, on an Indonesian island, where humans became dwarfs of 1m high and 25 kg. The brain consumes 25% of the body's energy when the body is at rest. Standing upright was an advantage to look in the savanna, but for women this implied narrower hips, constricting the birth canal, favoring earlier birth (since the head were generally getting bigger). Raising children then required social skills "it takes a tribe to raise a human". Humans have mostly been at the middle of the food chain, scavenging bones leftovers from other animals. Homo sapiens jumped at the top of the food chain faster than any other species, and the ecosystem didn't have the time to adapt. Cooking kills germs and parasites, eased the chewing and digestion. 5 hours a day of chewing for chimpanzees against 1h for humans. Since both the brain and a long intestinal track are huge energy consumers, it is possible that the growth of one and shortening of the other were linked. It is surprising that Homo Sapiens came to be the only human species remaining. The interbreeding theory states that people of today are results of interbreeding between species which would also dangerously mean that we could potentially talk of different modern human races depending on the location on earth. The Replacement theory states that Homo Sapiens has eradicated the other species. Recent evidence shows that the interbreeding theory is partly right since Europeans have about 1-4% of genetic code in common with Neanderthal. Similarly, australians have 1-6% in common with Denisovan DNA. It is clearly not a full merger though so some extinctions must have occurred either due to competition on resources or eradication: "too familiar to ignore but too similar to tolerate".