In Thayer's article, he attempts to incorporate Darwin's evolutionary theory into international security studies. The article seeks to answer a central question: what are the implications of evolutionary theory for realist international security theory, and how can peace be achieved if war is part of human nature? This article agrees with Thayer that evolutionary theory provides a scientific theoretical foundation for realism and is the ultimate cause of wars and ethnic conflicts, as well as the assumption that the origin of war is inherent in human nature as part of their history evolutionary. This paper will also suggest that a balanced structure of the world could contribute to temporary peace. But it should be noted that the theory is also limited as evolutionary theory cannot fully explain many other forms of security problems such as civil wars and terrorism. To review Thayer's article, first, the article will briefly explain how evolutionary theory acts as an ultimate cause for realist theory in terms of two human traits: selfishness and dominance. Next, the article will discuss the implications of evolutionary theory in international relations. This article will also evaluate the theory by comparing it with Waltz and Gleditsch's theory of peace and war. Finally, I will conclude the article by summarizing the main points. Thayer seeks to understand evolutionary theory as the ultimate cause of realism. In evolutionary theory, humans like other animals must evolve to survive and reproduce thanks to natural selection, which develops two fundamental human traits: selfishness and dominance (Thayer, 2000, p.130). To survive and keep fit, an organism tends to put its own security before others and according to Evoluti... middle of paper......densifies the understanding of international relations and correspondingly broadens the understanding of security. Based on the theory of Thayer and Waltz, the paper suggests that the structure of the international system is central to international security and that achieving peace requires appropriate strategies to balance power relations. Although it should not be ignored that the theory of evolution still falls within the realm of realism, as many other forms of complex security problems are inexplicable. Reference: Gleditsch, N.P. (1999). Peace and democracy. Encyclopedia of Violence, Peace and Conflict, 2, 643-652. Thayer, B. A. (2000). Leading to Darwin: evolutionary theory, realism and international relations. International Security, 25(2), 124-151. Waltz, K. N. (1988). The origins of war in neorealist theory. Journal of Interdisciplinary History, XVIII(4), 615-628.