The book details the "natural history of our political orientation". It is about how our political orientaion is shaped by evolution.
Our attitudes to the three aspects of tribalism, inequality and human nature are identified as the three cornerstone that shape our political orientation. These three aspects are common denominator among the various social psychology tests. Other than that, the author didn't present why it is these three, rather than others, which makes me hard to memorize all the three aspects.
To start with, the author shows the consistent statistics that personality outcompete incomes in predicting political affiliation and thus voting results. Then, the author starts to explain the evolutionary origins of the personalities, and how evoluationary forces shape populations' personality and simultaneously policatical orientation. Natural selection applys to groups of people and selects phenotypes through reproductions. The phenotypes happens at three different level, national, family's and individual's.
Tribalism is about "conflict among the nations". In evolution, tribalism takes effect through optimization between inbreeding and outbreeding. Outbreeding brings about genetic diversity, which is evolutionary beneficial against environmental changes; while inbreeding maintains stability against "enemies" and prevent from unintended vulnerabilities. The existence of optimal genetic distance for highest fertility delineates human populations, and form tribals. A side argument from this topic is human beings do not mate randomly. Mating process is influenced by genetics, significantly related to the optimal genetic distance for highest fertility.
Attitudes towards inequality is about "conflict among families". This section include discussions about gender inequality and order of birth. It has been repeatedly shown the higher gender equality accompanies liberalism. The interesting part is birth order's influence on political orientation. First born tends to be more convservative, respecting hierachy; while second born tends to be more liberal. The evolutionary force at play is that second born better identifies their own niche with differentiation from the first born in order to compete for resources from parents. That the first born tends to be more conservative is a result of first born's responsibility to take charge of the family, and maintaining order is a good strategy.
Attitudes towards human nature is about "conflict insice the conscience". In this section, altruism and self deception are key topics. The book The Selfish Gene explains the altruism very well. If we understand that natural selection also applies at gene level with the goal of its abundance at group lelve, then it's not difficult to understand individuals show altruistic traits. The part on self deceptions is really about how easy it is for leaders to cheat. Cheaters exist because they benefit if they are among the few in the group, which is shown in experiments like repeated Prisoners' Dilemma. The incentive to cheat only gets higher when power increases.
At last, I want to echo the author's recommendation in that by understanding how we and others naturally have certain political orientation can we be more sympathetic towards each other. Such mutual understanding is only helpful in resolving conflicts.