The Descent of Man/Chapter V
Darwin begins this chapter by explaining Wallace's views on man's evolution, i.e, that with the development of human intellect allowing him to make tools and shelters against a variety of climates, man would not have been as exposed to natural selection except as it related to his intellect. The more intelligent and creative people were more likely to survive.
Darwin restates the point that the desire for the praise of peers led to habitual social behavior. This can be seen in animals like dogs as well as "savages" and probably helped to naturally select those who worked with others of their species. He also touches on the question of the beginning of civilization and why some cultures progress and others don't.
Under "Natural Selection and Civilized Nations" Darwin points out that civilization has led to activities that enable the weaker members of society to survive and multiply while war carries off the fittest. He also discusses the relative merit of primogeniture and inheriting wealth.
In the subsection on "Hereditary Genius" Darwin states that the more intelligent will have a greater effect on society through their works as well as their children. He quotes statistics on the mortality rates of married and unmarried men and contradictory evidence on the effect of moral behavior on population growth. He also warns that natural checks to population increase among the morally inferior will not always keep them from overwhelming and reversing the progress of a society.
Looking at ancient Greece or sixteenth century Spain, he wonders what had stopped those cultures from taking over Europe. The United States appears to Darwin as a very good example of natural selection. At the same time Darwin acknowledges that progress comes from education of the young and "a higher standard of excellence...embodied in the laws, customs and traditions of [a] nation..." This in turn comes from a desire for approval which is a social instinct.
Finally Darwin holds that all "civilized" societies arose from "barbarous" ones. As examples he points to ways of writing, superstitions and trials by combat which have persisted through the ages.