Aggression is discussed in the context of human evolution and social behavior. The authors argue that, while aggression can be a part of human interactions, the ability to manage and mitigate aggression through cooperation and empathy that has allowed humans to thrive. This concept of aggression is central to understanding the contrast between the competitive and cooperative aspects of human nature.

Anthropomorphism is the attribution of human traits, emotions, or intentions to non-human entities. In the book, this term is discussed in the context of human relationships with animals and how anthropomorphism can both positively and negatively influence our understanding of them. Anthropomorphism is a double-edged sword, helping us empathize with animals but also leading to misconceptions.

Cooperation is a foundational theme in Survival of the Friendliest. The authors assert that cooperation has been crucial to human evolution, enabling the formation of complex social structures and communities. By working together, humans have been able to achieve feats that would be impossible individually. The book explores numerous examples from history, anthropology, and animal behavior to support this idea.