Chapter 13 was about social psychology more than anything and the main part was conformity and grouping. Human responses to social pressure are closely related to their own individual upbringing and to the cultural differences, but the main point being is that people end up coming together for a number of reasons. As explained in the book people with lower self-esteem are more prone to conforming. Cultures have impacts on this too because Asians are more prone to conform than are Americans but that is because they have a more collectivist culture. Grouping on the other hand is due to humans not wanting to be lonely. When we go without social contact for a long period of time we are doing the oposite of what our biology tells us to do which is to seek out bonds and connections between people.