In fact, detailed anthropological evidence shows that, for foraging peoples, harmony was maintained very incompletely and with a great deal of effort. Homicide, feuding and minor offences were common enough. But what is significant is the consistent effort that is made to contain them. For instance, there are reasons to think that inter-group competition was particularly strong during the climatic disturbances of the Palaeolithic period. Groups with altruistic, generously minded members might well have survived such an ordeal better than those composed entirely of dedicated egoists.
Human nature is a puzzling topic.
His remarkably sane approach, comprehensive yet enterprising, helps us to understand it better.