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 infantвЂ™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. An upright gait required narrower hips, constricting the birth canal вЂ“ and this just when babiesвЂ™ heads were getting bigger.

To this very day, humankind has been paying for its lofty vision and industrious hands with backaches and stiff necks. Adjusting to an upright position was quite a challenge, especially when the scaffolding had to support an extra-large cranium. The skeleton of our primate ancestors developed to support a creature that walked on all fours and had a relatively small head. Standing up, itвЂ™s easier to scan the savannah for game or enemies, and arms that are unnecessary for locomotion are freed for other purposes, like throwing stones or signaling.

ItвЂ™s one of natureвЂ™s biggest mysteries.ДЄnother singular human trait is that we walk upright on two legs. What then drove forward the evolution of the human brain? Frankly, we donвЂ™t know. For more than 2 million years, human neural networks kept growing and growing, but apart from some flint knives and pointed sticks, humans had precious little to show for it. But cars and guns are a recent phenomenon. Today our big brains pay off nicely, because we can produce cars and guns that enable us to move much faster than chimps, and shoot them from a safe distance instead of wrestling. A chimpanzee canвЂ™t win an argument with a Homo sapiens, but the ape can rip the man apart like a rag doll. ItвЂ™s hardly a foregone conclusion that this is a good strategy for survival on the savannah. Like a government diverting money from defence to education, humans diverted energy from biceps to neurons. Firstly, they spent more time in search of food. Archaic humans paid for their large brains in two ways. By comparison, the brains of other apes require only 8 per cent of rest-time energy. It accounts for about 2вЂ“3 per cent of total body weight, but it consumes 25 per cent of the bodyвЂ™s energy when the body is at rest. ItвЂ™s not easy to carry around, especially when encased inside a massive skull. The fact is that a jumbo brain is a jumbo drain on the body. Most notably, humans have extraordinarily large brains compared to other animals.Д«ut if giant brains are such a good idea, why are they so rare in the animal kingdom? The truth is that from about 2 million years ago until around 10,000 years ago, the world was home, at one and the same time, to several human species.Дespite their many differences, all human species share several defining characteristics. This linear model gives the mistaken impression that at any particular moment only one type of human inhabited the earth, and that all earlier species were merely older models of ourselves. ItвЂ™s a common fallacy to envision these species as arranged in a straight line of descent, with ergaster begetting erectus, erectus begetting the Neanderthals, and the Neanderthals evolving into us. Yet the real meaning of the word human is вЂњan animal belonging to the genus Homo,вЂќ and there used to be many other species of this genus besides Homo sapiens. We are used to thinking about ourselves as the only humans, because for the last ten thousand years, our species has indeed been the only human species around. Not only do we possess an abundance of uncivilized cousins once upon a time we had quite a few brothers and sisters as well. But itвЂ™s like these people havenвЂ™t spoken to anyone outside of their narrow field of expertise in decades itвЂ™s like they forgot the humanities existed.Homo sapiens has kept hidden an even more disturbing secret. And by the way, heвЂ™d like to sell you a new carвЂ¦.IвЂ™ve been struck, watching Harar speak at of which are tech or economics related - by the reverential way.hosts and audience members look at him.

HeвЂ™s like a car salesman whoвЂ™s convinced you that cars donвЂ™t really matter, theyвЂ™re just figments of our imagination. When Harari wonders aloud, вЂњMaybe IвЂ™m missing something?вЂќ I think heвЂ™s right. Shawn Vandor, an expert on the ethics of donor insemination wrote, вЂњIf you accept HarariвЂ™s thesis-that we live in a new paradigm, the quality and composition of which resembles nothing weвЂ™ve ever previously encountered-then one is tempted to accept the possibility that maybe we do live in an all-new moment in which Silicon ValleyвЂ™s love of Harari is, in fact, a sign of HarariвЂ™s rightness and, by extension, their own.

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