Darwin and International Relations is an outstanding contribution to both international relations theory and social sciences. At a time when academics often specialize narrowly in ways that block potentially fruitful interchange between disciplines, Bradley Thayer has demonstrated the value of moving beyond such insularity by linking theories of human social behavior to the life sciences. His book provides a model of open-minded and balanced expansion of the theoretical context underlying the field of international politics.

The first chapter explores the reasons for linking the social sciences to evolutionary biology, showing that while it is useful to remember the dangers of simplistic reductionism and prejudice, contemporary Darwinian biology is quite different from the erroneous stereotypes of “Social Darwinism” and has much to offer contemporary scholars. Next, Thayer presents a brilliant analysis of how contemporary Darwinian studies of evolution and human behavior can provide a solid basis for both “realist” theories of international relations and “rational choice” approaches throughout the social sciences. As he points out, theories tracing human behavior to self-interest can enormously benefit from the biological view of natural selection and social behavior as the result of a species’ evolved behavioral repertoire—what philosophers long called “human nature”—and the environment (ecology) as well as historical antecedents. Unlike the rigid distinction between nature and convention—or the contemporary dichotomy of “genes versus environment”—Darwinian biologists today explore complex interactions between multiple causal factors and influences. The results avoid the dual traps of forcing all analysis into a simplistic model (such as the view of the “balance of power” as a universal characteristic of international politics) or insisting that social science cannot go beyond the description of historically unique conditions.

In the third chapter, Thayer applies this interactionist approach of biologists to the phenomena of war as a consequence of both ecology and human nature. Thayer tests the theory by exploring warfare and inter-group violence prior to the emergence of the modern nation-state, with a special emphasis on conflicts in “stateless societies.” This discussion will be invaluable to scholars in international politics because it expands the database for theoretical consideration to many human societies whose experiences provide context and challenge for a generalized theory of international relations. Moreover, this chapter will be exceptionally significant to students of political philosophy who teach and reflect on the adequacy of the concepts of the “state of nature” and the contractual explanations of the origin of sovereign states in the works of Hobbes, Locke, or Rousseau.

Thayer goes on to provide a broader analysis of war and human evolution. A general theory of international conflict needs to be tested against phenomena as diverse as warfare among ants and fighting in pre-literate (“primitive”) human societies. While invaluable, this discussion may have less contemporary relevance than the fifth chapter, which explores the ever-present distinctions between “ingroups” and “outgroups” that so often give rise to ethnocentrism and violence. Here, one must emphasize the immense flaw in “neo-realist” theories of international politics that limited the phenomena to be studied to the actions of sovereign nation-states. After the terrorist attacks of September 11, 2001, and the widespread threat of Al Qaeda and other Islamist groups, it is time to admit that over the last few years the political science discipline has generally failed to identify many serious threats to US security.

These failures of research in international politics are not limited to minor issues unrelated to critical policy decisions. Whatever the final evidence on Saddam Hussein’s “weapons of mass destruction,” it is time to reflect on evidence that the Central Intelligence Agency (CIA) warned both US Presidents Bill Clinton and George W. Bush of the imminent danger of an attack by Osama bin Laden. Even more important is the report that, at the time Clinton was confronting impeachment, the CIA developed a plan to kill bin Laden which Clinton did not authorize due to his fears that failure or inadvertent killing of other leaders would have unacceptable consequences. In short, by focusing on sovereign states to the exclusion of “non-state actors,” the bias of neo-realist theories of world politics may well have contributed to the error of planning a war against Iraq before September 11, 2001, then claiming that Al Qaeda’s attack was an act of “state-sponsored terrorism” legitimating the unilateral removal Saddam Hussein’s regime by the United States.

By basing the theory of international relations in evolutionary biology, Thayer shows how war, ethnocentrism, and ethnic conflict can be understood as responses to varied configurations of environmental and demographic factors that need to be considered in a broader, interdisciplinary framework. While similar benefits would accrue in other areas of the social sciences, using theories and concepts based on Darwinian biology that still encompass human history and cultural variability is of particular benefit when exploring issues of war and peace between states. Not least of these benefits would be to link a clearer understanding of such factors as demography and economics in the origins of ideological extremism and between-group violence, which can obviously arise within a nation-state (as recently in Haiti) as well as between sovereign nation-states. Overall, therefore, theorists of international politics could both improve their own subfield and can help lead other social scientists to confront the fact that “continued advances of evolutionary biology—especially in ethology, genetics, and neuroscience—will reveal much about human behavior and make it difficult for social science to exclude their knowledge.”

In assessing Thayer’s brief introduction to the principles and findings of contemporary evolutionary biology, one could of course suggest additional citations that have been published after the manuscript was completed, such as Matt Ridley’s new Nature via Nurture (which provides a sustained explanation of the error of putting “versus” between “nature” and “nurture” and deftly suggests how Aristotelian teleology might be more relevant than the rigid dichotomy between genes and environment). Still, it may be appropriate to mention that new work only reinforces the perspective developed in Darwin and International Relations.

Whereas many social scientists had assumed that ethnicity and kinship were no longer central to “modern” politics, the contemporary media makes it clear that the broad focus of Thayer’s book is invaluable. The theoretical framework integrating evolutionary biology and social science combined with the outstanding use of empirical materials give this book the potential of making a major contribution to the understanding of world politics, war, and the international system.