Harari briefly touches upon two conflicting theories as to what happened to our humanoid brothers and sisters ie thw question as to why there were numbers of different members of the Homo genus, and now there is just one. The 'replacement' theory has it that we killed out all the opposition as we encountered them, with denisovians and neanderthals going to the wall in the face of sapiens greater agression and intelligence. The 'interbreeding' theory [which Harari says is gaining significant ground as modern mapping tecniques compare the genetic material of Africans, Europeans and Asians with those of our brother and sister geni] has it that we merely [at least to a degree] absorbed the other Homo varieties by interbreeding whenever we encountered them. That our three major 'types' possibly being reflective of genetic differences going back tens of thousands of years, is of potentially 'political dynamite' levels of significance is not lost on Harari; he absolutely recognises the potential for abuse of such types of study and makes it clear he does so.
He also discusses the idea of a 'cognitive revolution' that apparently occured between 70 and 100,000 years ago that saw a major change inb the way different parts of the brain could communicate with each other and which seems to be the crucial development that projected us above our rival Homo geni in respect of our cognitive abilities. The first thing this enabled was development of language that was capable of carrying much more information. Where previously we could say "Watch out - Lion!", now we could say "I saw a lion by the bend in the river this morning but now I think it's gone." Once we could do this we could do two other crucial things. First we could gossip. Trivial it seems but Harari believes gossip is so fundamental to what makes us us that still to this day we all do it nearly all the time. It's what allows us to form bigger groups that still cohere; a 'jungle' network of proto-journalists who spread word about who could be trusted, who could not, what to expect from this person or that etc, etc. In this way we could form larger groups without the need to intimately know every member. Group size was expanded even further as a result of one final development that our new brains gave us - the ability to believe in totally imagined things, things that have no basis in reality whatsoever; Gods. The development of shared delusions allowed for connection with disparate groups of individuals who in the past would only ever have been viewed as enemies. Now there was a cultural connection that allowed for safe gathering even among groups whose activities and manners differed widely in all other respects. "They're OK - they follow our God too" became the mantra that allowed for almost uinlimited connectivity between human beings - a faculty never seen before anywhere in the animal kingdom and one that serves us well to this day. Human rights, says Harari, fall into this catagory. They don't have any objective existance outside our imagination. We're not born equal and we never were. Capitalism is another such imaginary binding medium - the one that holds the whole world together today and no less a religion than Catholicicism or Sun-worship before it.
Harari slaughters many sacred cows on his journey through history [not least his brutal description of what we do to animals to ensure our supply of cheap food] and at the end finishes up where we are today. We will, he says become Gods. We'll conquer death, travel the Universe and know all there is to know - if we don't kill ourselves first. I'll leave you with his final passage;
We are more powerfull than ever before, but have very little idea of what to do with all that power. Worse still humans seem more irresponsible than ever. Self-made Gods with only the laws of physics to heep us company, we are accountable to no-one. We are wreaking havoc on our fellow animals and on the surrounding ecosystem, seeking little more than our own comfort and amusement, yet never finding satisfaction.
Is there anything more dangerous than dissatisfied Gods who don't know what they want?
]. The title alone somewhat causes a slight abrasion of my sensibilities! 
- but the ideas are undeniably interesting [especially his depiction of the capitalist system as having all the attributes of a religion; gosh I wish Z. would read that! 