In Christopher Boehm's earlier book Hierarchy in the Forest: the Evolution of Egalitarian Behavior (1999), he describes how hunter-gatherer and horticultural societies created egalitarian societies. The band or tribe members co-operated to prevent "alpha" type males from dominating their group. Having language helped them achieve this political equality, which chimpanzees would like to achieve and occasionally try to achieve but cannot maintain. Boehm is both an anthropologist and a primatologist and has studied egalitarian band, tribe and village customs and chimps in the wild. Without language that allows them to communicate and better co-operate, chimps end up with hierarchical societies. Human's egalitarianism is partly "natural" i.e. DNA driven and also made possible by abilities like language facilitated by DNA. Egalitarianism is the result of actions and a culture i.e. learned behavior. It is a question of the actions by all the adult members of the society to block potential tyrants or bullies from using physically force to dominate their group. It allows most males to have mates and requires hunters to share equally the meat of a large animal kill among all the members of the band. It requires alpha types to be generous, not aggressive, and not able to give orders or even assume "airs" of superiority.
In Moral Origins, Boehm looks at the evolution of conscience and the sense of shame, linked to the nearly universal (psychopaths do not have it) physiological response of blushing. He writes that only when humans achieved egalitarianism could human morality evolve. He dates these developments tentatively. Egalitarianism started evolving 250,000 thousand years ago and human morality was more or less completed by 50 thousand years ago. By that time, the weak, but clearly evident, (for example when young men volunteer for the military to help their nation) human propensity to altruism, which is defined by biologists as extra familial generosity, had evolved. Boehm writes that it evolved by "social selection" not natural selection. In egalitarian bands, the vast majority of the band selected the traits it most wanted of its members. A tyrant would be gossiped about, coldly greeted, directly talked to, kidded, ridiculed, shunned, ostracized or even executed. It is clear the final two actions changed the gene pools. With positive reinforcement, the generous, emotionally tranquil, and not easily angered were seen as better marriage or hunting/gathering partners. These desired traits and individuals were socially selected and affected human gene pools.
This version of the human story explains a difficult problem for peace and justice activists. Posed as a question: if human beings are by nature selfish or self-interested as mainstream social scientists assert, how can we create the kind of society we want? We know the answer intuitively. If the vast majority of people learn to cooperate, they can use nonviolent methods to force an altruistic morality on our alphas. Alphas may have talents that help societies, but they cannot use their status to dominate others. Counter intuitively, it is in the self-interest of the vast majority to create a society with an altruistic culture, for it benefits all. Conversely, the desire for upward mobility in a ranked system and the illusion that a person is just "one break away from making it big time" is one of the biggest barriers to the solidarity needed for such an optimal society. American culture has always nourished that individual desire and that illusion.
If it is true that human morality could not evolve in prehistory until our ancestors achieved egalitarianism, what has happened to human morality since? In strongly hierarchical societies like ancient Rome and the America of plutocracy and empire, most people sense a "breakdown of morality". The upshot of Boehm's thinking is that we, here in the USA, need to recreate an egalitarian society or at the least a true equal opportunity society. Only then, when everyone has the necessities of life and some dignity, can we say we have become moral.