In my view, debates concerning whether kin selection, individual selection, group selection or multilevel selection are ‘true’ are ill-conceived. These are merely different frameworks for thinking about evolutionary change. Since any two of these frameworks, independently brought to bear on the same question, can result in similar answers, it is perhaps more productive to ask which level or levels of selection are the more useful or natural to think about specific problems.
One problem that has interested a great many researchers, including the entire field of international relations (IR), is how to explain the dynamics of interaction between sovereign territorial states (i.e., ‘countries’). Here I first argue that the group, specifically the sovereign territorial state, is the most natural level of analysis in IR which has, in fact, long been the conventional wisdom in the field. Second I argue that developing a more formal theory of selection at this level in IR can add much to the “conventional historian’s account” of the field.
What is the most useful unit of analysis in international relations? In answering this question I will look at the works of three prominent IR scholars, Kenneth Waltz, Alexander Wendt, and Robert Keohane. These scholars are not-cherry-picked, but are the researchers most associated with the three most prominent paradigms in modern international relations theory and were named, in a recent survey of over 1,500 IR scholars, the field’s three most influential scholars of the last 20 years. Their approaches to international relations can thus be considered roughly representative of the field.
The most thorough examination of the proper unit of analysis in IR is Waltz’s seminal 1959 book,Man, The State and War . He asks whether international warfare is best understood by appeals to individual psychology, appeals to domestic political institutions, or appeals to states’ interactions with each other. Although acknowledging that “some combination of the three… may be required for an accurate understanding of international relations” , he finds that these levels of analysis are unequal partners.
Waltz, importantly, finds little utility in appeals to evolved psychology in IR, writing:
While human nature no doubt plays a role in bringing about war, it cannot by itself explain both war and peace, except by the simple statement that man’s nature is such that sometimes he fights and sometimes he does not. .
He goes on to argue that since human nature should be relatively constant and states are not always at war or always at peace,one must look above the level of the individual to explain the conditions under which war occurs and the conditions under which it does not. He eventually settles on the interactions between states, especially the modern territorial states, as the most appropriate level of analysis.
Sovereign territorial states have many properties that lend themselves naturally to the logic of multilevel selection [5, 6]. First, they are territorial, meaning that an individual’s group membership can be more-or-less defined by looking where he or she lives on a map. Second, they are sovereign, meaning that they have a government with sole legal authority over the affairs within its territory and the legal authority to negotiate with others outside of it. This allows for an easier demarcation of internal and external dynamics of the group. Third, as political scientist John Mueller put is, once the major powers signed the UN charter “they essentially declared international boundaries sacrosanct no matter how illogical or unjust some of them might seem to interested parties.”  This allows us to assume low rates of what Samir Okasha calls “multilevel-selection 2” (MLS2), where selection occurs as groups dies off and other groups are born. Instead we can restrict our analysis primarily to MLS1, where groups are not removed from the system, but selection acts to change the frequency of traits both within and between them .
Waltz argues, in his 1979 book, Theory of International Politics, that states are most usefully thought of as “unitary actors” with their own preferences and motivations. It is not that Waltz thinks states actually lack internal divisions, but that for most questions in IR the unitary actor model does just fine without appeals to lower levels of analysis . This line of reasoning has been very productive in IR theory, and although I lack space for a complete review, the unitary actor assumption is commonly made in theoretical models of state behavior, including James Fearon’s influential bargaining models of war , and rarely has to be justified to a political science audience.
Waltz’s theory of international politics is explicitly evolutionary. Noticing that the death rate of states is low (thus, as pointed out above, limiting the importance of MLS2), Waltz’s selection operates through success-biased emulation. He writes that “the theory says simply that if some [states] do relatively well, others will emulate them or fall by the wayside.” 
Wendt’s 1999 Social Theory of International Relationsis often taken to be a critique of Waltz’s book. But in it he not only defends the unitary actor assumption, but considers it “essential to both the explanatory and political aspects of the states systemic project.”  However, Wendt goes much further than Waltz in explaining the evolutionary mechanisms underlying international change. To Wendt, important questions in IR cannot be understood without understanding the “distribution of ideas in the system,”(where ‘ideas’ are roughly equivalent to Dawkins’ memes or Boyd and Richerson’s cultural traits). Wendt stresses that ideas change through a process of “cultural selection” which operates through states’ imitation of successful states. Since he also accepts that states do not often die, Wendt’s theory is ultimately one of MLS1 selection – where selection operates by changing the frequency of ideas within and between groups.
Robert Keohane is the unitary actor assumption’s most prominent critic . However, even he stresses the primacy of groups, just ones operating at other levels of organization. In addition to states he argues for the importance of international organizations (such as the United Nations), transnational organizations (such as terrorist groups and multinational corporations) and domestic institutions (such as legislatures). His theoretical framework is one of institutions. Although his theory is the least explicitly evolutionary, others have argued that institutions are difficult to explain without evolutionary principles. For example, Elinor Ostrom, in a recent review of her institutional analysis framework, finds that “developing formal methods for examining diverse processes of structure change over time is an important next step for scholars who have mastered some of the new techniques derived from the study of genetics.” 
In my handful of presentations to political science audiences I have never once had to justify my choice of accounting for the payoffs to state behavior at the level of groups. It is easy to see how scholars in IR have settled on groups as the proper and most useful unit of analysis. Say one is interested in the spread of democratic forms of governments or interstate war. While it is easy to see bicameral legislatures or conscription armies as properties of groups, it is more difficult, at least for me, to see how their costs and benefits can be easily partitioned down to the level of individual selection.
Using IR’s three most influential scholars as examples, I have argued that groups are the most natural level of analysis for answering questions in IR and, specifically, MLS1 on cultural traits or ‘ideas’ is the most important evolutionary framework. But, as Pinker asks, “what does ‘natural selection’ add to the historian’s commonplace that some groups have traits that cause them to grow more populous, or wealthier, or more powerful, or to conquer more territory, than others?”
At first this seems a silly question, akin to asking “what does ‘natural selection’ add to the naturalists’ commonplace observation that some organisms have traits that cause them to have more offspring, control more resources, or live longer than others?” It is as if evolutionary theory should have both begun and ended with Darwin.
There are many suggestions in the writings of the above scholars, that a more formal theory of selection amongst groups has a lot to offer theories of international relations. However, since few scholars are trained in both international relations and evolutionary theory, the utility of natural selection to understanding state behavior is still somewhat of an open question. Perhaps the most prominent work in this vein, thus far, is a series of models and empirical analyses by Lars-Erik Cederman and colleagues [16-19] addressing the spread of democracy through what is known as the “democratic peace.” The democratic peace is a robust empirical finding that democracies tend not to go to war with each other. Cederman’s models show the conditions under which this property of democracies can allow them to spread at the expense of non-democracies. These are interesting models and important first steps to an understanding of the dynamics of democracy and peace in the international system. However, a greater understanding of the findings of evolutionary game theory can make them more useful.
For example, in one of Cederman’s models, democracies are ‘tagged’ so that they can recognize each other and cooperate, out-competing non-cooperative non-democratic states under a variety of conditions . At first this seems a ‘commonplace’ application of a robust empirical observation. However, as Cederman acknowledges, his model relies on the assumption that tagged states will not defect on these arraignments. In essence, a democratic tag is a perfect predictor of cooperation, what is known as a ‘green beard’ in evolutionary biology .
What evolutionary theory adds to this analysis is the non-obvious recognition that ‘green beards’ are unlikely to last long. The problem is that in the system Cederman describes selection for defection should act the most strongly on democratic tagged states, because they are more likely to be the benefactors of cooperation.
For illustration, suppose two democracies cooperate by mutually leaving their mutual border undefended so they can save on the cost of defending them. Meanwhile, their borders with nondemocracies are well defended. Now suppose one of these states is in need of resources that it cannot easily get through other means (such as trade). Which neighboring state is the least costly for it to invade? All things equal, it is the one with undefended borders – the other democratic state. Thus, in order for strategic tagging to work there must be some force maintaining the correlation between the tag and altruistic behavior. This is a general analytic finding in evolutionary theory , but perhaps not immediately obvious to an historian or political scientist .
In summary, the science of international relations has long recognized human groups as the most natural and useful unit of analysis in understanding its important questions. In fact, it is difficult to see how the selection on traits easily thought of as properties of groups, such as systems of government and foreign policies can be reexamined as the result of selection process operating primarily at the level of individuals. Even if it was possible, it is unclear why one would want to go through the mental and mathematical gymnastics required. I further disagree with Pinker that the understanding of selection on cultural traits has nothing to add to international relations theory and give an example where non-trivial applications of selection models can lead to novel insight.
1. Avey, Paul C., Michael C. Desch, James D. Long, Daniel Maliniak, Susan Peterson, Michael J. Tierney. 2012. The Ivory Tower Survey How IR scholars see the world. Foreign Policy Magazine. (http://www.foreignpolicy.com/articles/2012/01/03/the_ivory_tower)
2. Waltz, Kenneth N. 1959. Man, the State, and War. New York, NY: Columbia University Press.
3. ibid. p. 14
4. ibid. p. 29
5. Tilly, Charles. 1992. Coercion, Capital and European States. Wiley-Blackwell.
6. Spruyt, Hendrik. 1996. The Sovereign State and its Competitors. Princeton, NJ: Princeton University Press.
7. Mueller, John E. 2004. The Remnants of War. Ithaca, NY: Cornell University Press. (p. 67)
8. For a discussion of MLS1 and MLS2, see Okasha, Samir. 2006. Evolution and the Levels of Selection. Oxford University Press.
9. Waltz, Kenneth N. 1979. Theory of International Politics. McGraw-Hill.
10. Fearon, James D. 1995. Rationalist Explanations for War. International Organization, 49:379-414.
11. Waltz. Theory of International Politics.(p. 117)
12. Wendt, Alexander. 1999. Social Theory of International Politics. Cambridge, MA: Cambridge University Press. (p.243)
13. ibid. (pp. 5, 41, 96, 138)
14. Keohane, Robert O. 1984. After Hegemony: Cooperation and Discord in the World Political Economy.Princeton University Press.
15. Ostrom, Elinor. 2011. Background on the Institutional Analysis and Development Framework. Policy Studies Journal 39:7-27.
16. Cederman, Lars-Erik. 2001. Back to Kant: Reinterpreting the Democratic Peace as a Macrohistorical Learning Process.” American Political Science Review 95:15-31.
17. Cederman, Lars-Erik. 2001. Modeling the Democratic Peace as a Kantian Selection Process.”Journal of Conflict Resolution 45:470-502.
18. Cederman, Lars-Erik and Kristian S. Gleditsch. 2004. Conquest and Regime Change: An Evolutionary Model of the Spread of Democracy and Peace.” International Studies Quarterly 48:603-629.
19. Cederman, Lars-Erik and Mohan PenubartiRao. 2001. Exploring the Dynamics of the Democratic Peace. Journal of Conflict Resolution 45:818-833.
20. This is called a green beard, from a hypothetical example by Richard Dawkins where agents with green beards always cooperate with other green-bearded agents; Dawkins, Richard. 1976. The Selfish Gene. Oxford: Oxford University Press.
21. See Grafen, Alan. 1990. Do Animals Really Recognize Kin?” Animal Behaviour 39:42-54.
22. For a similar example see:
Riolo, Rick L., Michael D. Cohen and Robert Axelrod. 2001. Evolution of Cooperation Without Reciprocity. Nature 414:441-443.
Roberts, Gilbert and Thomas N. Sherratt. 2002. Does Similarity Breed Cooperation? Nature 418:499-500.