The revolutions described by Harari are what set in motion the cycle of life that produced modern day humans. First came the Cognitive revolution, with the key features of better skills to survive and groups of people organizing into cultures based on geographical locations. this formed the basis for tribes and other collective groups that would inhibit certain landscapes. We also took the step from being hunted by other predators to becoming the dominant member of the food chain not only in numbers, but also in intelligence. We were learning more and more every day and that information was being passed down to the next generation by word of mouth or genetics. The next revolution to impact human development was the Agricultural revolution. This was a time of gathering rather than gathering. Up until this point most of early humanity had been propel who followed herds of bison or elk (in the case of Montana Native Americans) around the plains to hunt them. Without the herd the tribe would starve and die of exposure to the cold. Meat, pelts, and bones were vital to their way of life and survival. Now the tribes found ways to reliably grow simple crops such as wild wheats and some fruit variants (most of which are ancestor to crops we grow today). These changes propelled us to become a thriving species and survive the world
But more than becoming a species that survived we had to become a species that thrived and dominated to endure the long term survival of the species. The theory that stands above the rest is the replacement theory that states that the reason all humans have very similar DNA is that the other species of homo died out due to not being strong enough. Hierarchy is not a DNA thing, it is an evolutionary thing. It came over time when our communities divided into social ranks with elderly, young, men, women. The survival of the fittest was in full swing during this time period to produce the dominant species of human.