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date: 25 April 2017

Evolution, Adaptation, and Imitation

Summary and Keywords

Evolution, as a biological process and a metaphor, has utility in our understanding of international relations. The former is largely inapplicable for obvious, conceptual, and empirical reasons; but the latter is more promising, though those who use it must be explicit about its limitations. There must be considerations on how evolution contrasts with conscious adaption and imitation, on the argument for the need to distinguish among them analytically and empirically, and on the further exploration of the different conditions in which these other two mechanisms might be relevant.

Keywords: adaptation, cooperation, ethology, evolution, evolutionary psychology, imitation, natural selection, war, empirical international relations theory


Evolutionary approaches are now widely applied in psychology, anthropology, and international relations to explain change, as well as its absence. Biological approaches assume that many human behavioral patterns are genetically determined. To understand such phenomena as hierarchy, mate selection and gender differences, rape, violence, and war, proponents of evolutionary approaches contend that we must understand how our ancestors benefitted from certain mutations. Social scientists and international relations scholars also use evolution as a metaphor, but many who do still rely on selection as a mechanism. Others implicitly rely on conscious adaptation and imitation, which are important mechanisms, but not evolutionary ones. I review these several approaches to change and assess their relevance to the study of international relations.

I open with a discussion of evolution and its mechanism of natural selection and look at how it is used in biology and international relations. I offer a critique of evolutionary psychology, the dominant evolutionary research program in our field, drawing on understandings among biologists about how evolution works, exploring the assumptions and logic of evolutionary psychology, and querying evidence that advocates offer in support. I suggest that practitioners of evolutionary psychology make great and unwarranted leaps from genetic change to political behavior. They arbitrarily identify some social proclivities, as opposed to others, as products of evolution and defend them as advantageous (i.e., promoting survival and reproduction) for our ancestors. Their attempts to explain the persistence of conflict and war sometimes reveal more about the normative commitments of researchers than they do about evolution or international relations (Dusek, 1999; Bell, 2006; Lebow, 2013).

Evolutionary psychology is literal in its approach to evolution. It focuses on genes or individuals as its units, reproduction as its enabling process, and natural selection as its mechanism. Other evolutionary approaches depart from biology by using states as their units and what I call “unnatural selection” as their mechanism. They argue that strategic, economic, or political opportunities and constraints reward some behaviors and structures and punish others, thereby encouraging convergence. Some studies that claim to be evolutionary explicitly or implicitly attribute convergence to conscious adaptation, which is not an evolutionary mechanism. Convergence might also be the product of imitation, another mechanism, and one that is undertheorized.

My review prompts several conclusions. We need to be much more explicit about identifying the mechanisms we expect to do our work, describe how they work, and the conditions in which they do. We must distinguish more effectively between different mechanisms and think about how they might interact, possibly, but not always, in reinforcing ways. Conceptual advances require an adequate empirical base, and good theory should guide empirical research. Better discrimination among mechanisms represents an important input into this recursive process.

Natural Selection and Human Behavior

Evolution has become a more fully elaborated paradigm since the days of Darwin. It rests on a foundation of genetic variation and competition among individuals and species for survival in diverse and changing ecological niches. Its principal mechanism is natural selection. Mutations give rise to morphological changes, some of which confer advantages to individuals by making them more likely to survive and reproduce. Over time, inheritable advantages spread to varying degrees among a species. A recent example concerns the enzyme that allows us to digest and benefit from milk products after weaning. Different mutations affecting the controlling mechanism of this process appear to have arisen among different peoples in diverse geographical locations (Ingram, Mulcare, Itan, Thomas, & Swallow, 2009). They spread because of the nutritional advantage they confer.

Natural selection is universally accepted within the scientific community. It is not, however, free of controversy. Some biologists contend that it offers a reasonably complete account of evolution while others insist that it needs to be augmented by other mechanisms. These include non-Darwinian evolution arising from random mutations that do not produce observable traits and are therefore not selected, structural constraints that produce imperfect bodily adaptations, and geological and astronomical catastrophes that cause mass extinctions.

Evolution became prominent again in social science with the publication of E. O. Wilson’s 1975 book Sociobiology: A New Synthesis, and his subsequent Pulitzer Prize winning 1978 work: On Human Nature. Wilson (1978, p. 595) defined sociobiology as “the systematic study of the biological basis of all social behavior.” It emphasizes the survival of organisms by virtue of their fitness and gene transmission through reproduction. Many journalists wrote admiringly of Wilson’s books, but they provoked critical reviews by scholars, including Elliot Sober and Richard Lewontin (1982) and Gould (1997). The controversy surrounding Wilson encouraged the search for archeological and ethnographic evidence that could be used for and against evolutionary models of human behavior. Little to no evidence has been found for Wilson’s claims (Hamilton, 1964; Trivers, 1971, 1974; Dawkins, 1976). His sociobiology has been superseded by evolutionary psychology. Evolutionary psychology attempts to identify mechanisms that arose to meet the environmental demands faced by our ancestors. It works on the assumption that such mechanisms became widespread and were transmitted genetically to present-day humans.

The leading research program in evolutionary psychology is associated with the work of John Tooby and Leda Cosmides (Tooby & Cosmides, 1990a, 1990b, 2005; Cosmides & Tooby, 2013). They attempt to finesse the problems associated with Wilson’s sociobiology by focusing on psychological mechanisms in lieu of behavior. These mechanisms are said to be mediated by experience and give rise to diverse responses under different conditions. Tooby and Cosmides further contend that mechanisms can produce novel outputs when people confront new challenges. They want such mechanisms to be catalogued and analyzed the way archeologists and anthropologists do cultural artifacts and practices. The goal is to identify their intended functions and the pressures that encouraged their spread through the population.

Tooby and Cosmides generated controversy with their claim that human minds are modular and that each module consists of a psychological mechanism. They describe these mechanisms as genetic adaptations that developed during the Pleistocene epoch in response to problems our ancestors faced (endorsements come from Pinker, 2002; Daly & Wilson, 1990; Buss, 2003). They further claim that all psychological mechanisms are evolutionary and that all branches of psychology must become evolutionary in focus (see Dunbar & Barrett, 2007 for elaboration).

Critics accuse Tooby and Cosmides of intellectual imperialism and of making a string of assertions not backed by empirical evidence. Sympathetic critics contend that they underestimate the variability of Pleistocene human societies and the diverse challenges they faced and that they ignore evolutionary pressures and responses prior to and following this era of human history. Less friendly critics question the existence or efficacy of the mechanisms emphasized by Tooby and Cosmides and their supporters. They point to the lack of evidence that any particular gene is responsible for any observable behavior, or question whether a gene that might have triggered a mechanism in an ancestral environment does so today (Gray, Heaney, & Fairhall, 2003; Buller, 2005; Mameli, 2012). They suggest that the environment has changed and affected human development. Contemporary psychological mechanisms might be novelties arising from the interaction of ancestral genes and new kinds of environmental problems and pressures (Elman, Bates, Johnson, Karmiloff-Smithy, Parisi, & Plunkett, 1996; Quaetz & Sejnowski, 1997).

Some scholars favorable to evolutionary psychology acknowledge that the diverse practices of humans are very much the product of culture and sustained by it. McDermott and Hatemi (forthcoming) offer a thoughtful analysis of the recursive relationship between genes and culture. Their core argument is that institutional differences emerge in part because of ecological pressures and resulting—and often reinforcing—cultural and biological adaptations. The examples they give are convincing and perhaps useful for understanding some kinds of macro phenomena (e.g., advantages of lactose tolerance for northern Europeans, destruction of native American cultures by imported pathogens) but say little to nothing about the social, political, and economic diversity we see among populations in what might be considered roughly equivalent environmental niches.1

The relationship between genes and environment is enormously complex and poorly understood. To date, evolutionary psychology does not cope well with this problem. Most studies speak of individual behavior in isolation, although they acknowledge that people are embedded in groups and cultures. Recent works are more understanding of the social nature of humans, and some attempt to build on this recognition. The “male warrior” hypothesis, for example, theorizes that certain kinds of coalitions are responses to external challenges, that the tendency to form and sustain such coalitions is reinforced culturally, and that it gives rise to hereditary mechanisms. A similar argument about coalitions is made by Lopez, McDermott, and Peteresen (2011). Such claims are highly speculative and often based on questionable inferences and highly selective readings of history and politics. Lopez, McDermott, and Petersen cite a study that finds that self-assessment of physical strength is one important cue that regulates an individual’s willingness to resort to force in conflicts of interest to make the case that the same holds true for the calculations of states in international conflicts. Generalizing between people and political units is always questionable, as is the assumption that most personal or international conflicts are about conflicts of interest. As initiators historically lose most of the wars they begin—more than 80% since 1945 (Lebow, 2010)—there is good reason to question leaders’ assessments of “strength.”

Evolutionary psychology reveals a distinct bias in its emphasis on the selfish and aggressive side of human nature. Analogizing from apes and their hierarchies, some writers assume a universal human drive for dominance (Wilson, 1975; Eibl-Eisbesfeldt, 1979, 1989; Pinker, 2002). Altruism is nevertheless widely observed. Many scholars drawn to evolutionary psychology believe this problem was resolved in the 1960s by W. D. Hamilton’s research on ants and bees (1964). Hamilton’s rule states that, ceteris paribus, a gene for altruism will evolve to stability whenever the benefits to the recipient—in terms of the number of future offspring born—exceeds the cost to the altruist—measured by offspring lost. R. L. Trivers extended this formula to include reciprocal altruism of nonkin (Trivers, 1971; Van Vugt, Roberts, & Hardy, 2012; Gintis, Bowles, Boyd, & Fehr, 2007).

More recent evolutionary accounts rely on kin selection theory. Anthropologist Boehm (1999, 2012) argues that altruism can be explained by the benefits it confers on one’s offspring. So too, he contends, can the emergence of equality as a principle and practice. Individuals who would otherwise be subordinate to alpha males form coalitions to keep the strong from dominating the weak. He alleges that such behavior became pronounced among hunter bands in the Upper Paleolithic era. Their more egalitarian lifestyle had important evolutionary effects over the following 1,000 generations. It produced changes in the human gene pools because groups that practiced sharing and encouraged sacrifice for the benefit of the group were more likely to survive than those who did not.

Boehm’s argument is based on speculation. We have no evidence that Paleolithic hunter bands were egalitarian or encouraged altruism. Natural selection is traditionally thought to work on individuals, not genes (Sober & Lewontin, 1982).2 The Boehm thesis further requires a gene, or suite of them, to encourage altruism. This gene or genes must produce no other effects that are harmful for individual survival.

Boehm, and many others who invoke evolution to explain social behavior, assume that biology, not culture, is responsible for altruism and egalitarianism. Do we need tortured and scientifically questionable evolutionary arguments in lieu of more empirically verifiable efforts to account for behavior in terms of learning and socialization? We have compelling evidence for cultural and political explanations, and, unlike evolutionary theories, they are better able to explain the enormous variation we observe in human societies across cultures and epochs. Biological explanations, by contrast, cannot account for the rise and fall of the values that encourage or discourage altruism and egalitarianism in societies whose population or genetic makeup has not significantly shifted in the course of these shifts.

Charles Darwin, a close reader of Adam Smith, did not subscribe to the one-sided view of human nature that is dominant in contemporary evolutionary psychology. He acknowledged diversity in social instincts and speculated that from the beginning of the human race people would have “some wish to aid [their] fellows, and some feeling of sympathy” (Darwin, 2004, pp. 101–131). He reasoned that any species endowed with well-marked social instincts would inevitably acquire a moral sense or conscience as soon as it developed sufficient intellectual powers. Darwin (2004) put more emphasis on culture than instinct in determining human behavior.

Noted ethologist Frans B. M. de Waal makes a different but reinforcing argument against those who draw analogies to apes in support of their claim that humans are aggressive by nature. There is just as much evidence among apes, he insists, for altruism and cooperation (de Waal, 2006). De Waal is not the only ethologist to warn against generalizing across primates, or between them and human beings (Wrangham, McGrew, de Waal, & Heltne, 1994; Wrangham & Peterson, 1995). The three African great apes live in hierarchical societies, but, de Waal observes, the same behavior can have different causes. It can be the product of evolution or represent adaptation to similar environmental pressures or constraints (de Waal, 2006). Ethologists and many philosophers stress the differences between humans and other primates due to our greater cognitive capacities, ability to reflect on our behavior, and construct and be guided by abstract ideas. They warn us against making facile comparison across species (van Schaik, 2012).

Evolution and War

Darwin developed arguments of great subtlety, and nowhere more so than in addressing the problem of aggression and war. Evolution, in his view, helped to account for the origins of the human species and its change and development over time. He recognized the endemic character of warfare but denied that it arose from instinctive urges for conquest. He considered war and cooperation in accord with human nature. He believed that the more violent forms of human conflict were declining, in part because of the development of sympathy. His theory requires this kind of flexibility because if structure determined behavior there would be no possibility for changes in behavior in response to environmental pressures.

In chapter five of The Descent of Man Darwin writes more about human sociability than about pugnacity. He offers considerable evidence of sociality among animals and argued that in humans it is the foundation for moral sensibility. Sympathy and concern for others is strengthened by the desire to win their approval and avoid their censure. With language, feelings of shame and guilt develop, and the possibilities of cooperation increase. Cooperation has selective value because groups have a better chance to survive than individuals, making it more likely that individuals in groups will reproduce. In contrast to animals, human altruism is more reflective than instinctive and is reinforced by experience and imitation. It benefits from a sense of diffuse reciprocity, whereby people hope for future rewards in return for providing favors or making sacrifices. Darwin acknowledged that people are continually at war and that social sympathy is mobilized to improve combat effectiveness. War in turn enhances social sympathy.

Darwin was of two minds about the future of war, but was more upbeat than not. He expected education to make ethical commitments more widespread and make altruism more habitual. There is a good chance, he thought, that it would promote wider circles of sympathy and reduce, if not ultimately eliminate, war among tribes, states, and empires. He nevertheless accepted that struggle is essential for human development and had the potential to become violent. He worried about degeneration, especially if civilized societies use their resources to protect the weak and uncompetitive and preserve lives through vaccination and other forms of medical intervention. He nevertheless approved of humanitarianism in general and regarded it as an expression of sympathy.

Proponents of evolutionary psychology do not share Darwin’s cautious optimism. They downplay sympathy and cooperation, emphasize the aggressive nature of human beings and attribute it to natural selection. Sexual selection operates by means of competition and intersexual selection. The peacock’s tail is a product of intersexual selection. Female peacocks respond to large tails, even though such tails make males more vulnerable to predators. Some scholars—mostly those in the evolutionary psychology research program—argue that violence is similar: aggression and “manliness” attract females but encourage behavior that may be dysfunctional in terms of survival (Liddle, Shackelford, & Weekes-Shackelford, 2012; Buss, 2003).

International relations scholars attracted to evolutionary arguments are more likely to argue that aggressiveness is highly functional, at least at certain stages of human development. Gat (2009) suggests that national identities can substitute for biological kin ties because “shared cultural traits function as cues for kinship.” He nevertheless warns (2000) against insisting on a primary motive for human behavior. A related argument, known as the “male warrior” hypothesis, maintains that tribalism developed in response to external threats or an early version of what Herz (1957) called the security dilemma. In-group members are treated well and out-groups malevolently. Cognitive mechanisms develop to encourage coalitions of in-group “male warriors” as they confer an advantage in the competition for security and scarce resources (Van Vugt, 2012; MacDonald, Navarrete, & Van Vugt, 2012). War is an extension of this behavior on a larger scale. According to Gorelik, Shackelford, and Weekes-Shackelford (2012), “institutional, regional, and global violence are rooted in our adaptations to seek, acquire, maintain, and utilize limited resources needed for survival and reproduction.”

Still other scholars connect violence to male dominance and the struggle for sexual partners. Wright (1995) maintains that this behavior reaches its zenith in despotic regimes. According to Wrangham and Peterson (1995): “Male coalition warfare is primal.” We are part of a group within the apes where males hold sway by combining into powerful, unpredictable, status-driven, and manipulative coalitions. This is “why humans are cursed with males given to vicious, lethal aggression” (ibid.). Rosen (2007) argues that many societies reward men who respond effectively to challenges. These men interact and reinforce their propensity to respond decisively to challenges. This behavior is sustained and further reinforced by institutions. Such men, he claims, evolve higher testosterone levels – a dubious claim as is the related one that higher levels have known behavioral implications. Rosen nevertheless this process can “create a self-sustaining cycle, producing individuals who are prone to dominance behavior” (Potts & Hayden, 2008, for a similar argument). Male dominance hierarchies in many societies and are accordingly associated with polygyny and higher warfare rates among tribal groups. Anthropologist Napoleon Chagnon documented such behavior among the Yanomamo people in the Amazon and is widely cited by evolutionary psychologists. Other anthropologists contest his account.3

The male warrior thesis has been mobilized to oppose women assuming combat roles. Women are said to degrade combat effectiveness by negatively affecting group dynamics. This in turn is attributed to sexual differences in how men and women relate and respond to adversaries. Hudson and den Borer (2012) offer evidence that men feel uncomfortable fighting alongside women and even more in taking orders from them (also Browne, 2012). These arguments are no different from those voiced seventy years ago by those who opposed racial integration of the American armed forces. In practice, white males accustomed themselves more rapidly than many expected to racial integration. This may also prove true of male soldiers, seamen, and aviators that serve alongside women (Kamarack, 2015).

Bradley Thayer’s Darwin and International Relations (2004) also reverses the arrow of causation. Instead of using evolution to explain war, he uses war to explain evolution. War is alleged to have enlarged the human brain by generating pressures for innovation in weapons, tactics, and communication. It is “the only” kind of activity that makes unlimited demands on the intellect and “so leads to intelligence” (Thayer, 2004, pp. 154–155). His only evidence for this striking assertion is citations of like-minded believers in evolutionary biology who make similar claims. Neither Thayer nor those who agree with him consider other human activities—e.g., the pursuit of food in the African savannah in the face of fierce predators or the shift from hunting and gathering to settled agriculture, and later, to urban life—that might have been equally cognitively demanding. Most troubling is the claim that a social need for some physiological attribute can bring it about through evolution. This contention violates conventional understandings of evolutionary theory, and Thayer offers no mechanism that might be responsible for it.

Thayer alleges that war promoted other evolutionary developments, most notably changes in the nervous system that make war emotionally and sexually stimulating, and warriors more sexually attractive to women. It is also alleged to have generated the cognitive need to categorize people in “us” and “other” binaries. For evidence, we are given autobiographical and other accounts of combat that speak of war’s arousal effects and how men late in life look back on it as their most exciting and meaningful experience. There are no interviews with women or other sources of evidence about their responses to men in uniform. In what is arguably Thayer’s greatest leap of inference, he asserts that “Just as alpha males living in . . . ‘dominance hierarchies’ bring stability and other important social benefits to the pack, herd, or pride, so too does the hegemon bring stability and benefits of other collective goods to international relations” (Thayer, 2004, p. 20).

Thayer’s thesis rests on the assumption that offensive realism is an accurate depiction of international relations rather than an ideology lacking empirical support. Thayer offers no discussion of efforts to reduce war and ethnic conflict through conflict resolution, institution building, economic development, and humanitarian intervention. They are presumably in conflict with our nature and doomed to failure. His selection of what is human and what is not is arbitrary, as is his claim that war is the most important of all human activities affecting evolution. He further assumes that successful warriors breed more successfully, another unsupported claim. Perhaps his most questionable claim is that group advantages, conferred by individual characteristics such as aggression, bravery, and loyalty, are somehow passed on through warrior genes and that natural selection does the rest.

It is, of course, unfair to judge a paradigm by the work of its least impressive representatives. Like Thayer, however, almost everyone who attempts to explain international relations in terms of biological evolution attributes dominance and war to the nature of the human male. Such authors cite the frequency and antiquity of violence, rape, and war as evidence. Some, as noted, make analogies to the great apes and describe dominance and violence as inherent to primates. Political theorists have long been wary of arguments based on human nature because of its almost inescapable selection bias. For centuries philosophers posited human traits consistent with the behavior they want to explain. Arguments of this kind—whether made by Hobbes, Rousseau, Hume, Schmitt, or international relations scholars—invariably tell us more about their political beliefs and projects than they do about ourselves and our ancestors.

Those who apply biological evolution to international relations almost invariably posit essentialist binaries between men and women. In practice, any behavioral trait, whether genetic or cultural, is rarely gender-specific, although it might be more pronounced in one sex than the other. Pinker (2002, p. 114) rightly observes that biology matters: “Some behavior must be affected by some genes, or we could never explain why lions act differently from lambs.” Dawkins (1976, p. 164) addresses the gender issue head-on. “It is still possible,” he writes, “that human males in general have a tendency towards promiscuity and females a tendency to monogamy, as we would predict on evolutionary grounds. Which of these tendencies wins in particular societies depends on details of cultural circumstances, just as in different animal species it depends on ecological details.”

Evolutionary approaches generally fail to distinguish war from violence. The latter is likely to be unorganized, committed by individuals or small groups, and emotionally driven. Group raids are more organized and may be planned in advance. Their aims are invariably short-term and motivated by revenge or by desire for women or access to water or fishing or hunting grounds. War is a distinct phenomenon and the product of large, organized political units, generally making use of special warrior castes or organizations. War is distinguished from violence by its political goals and the understandings participants have of its special character (Huntingford, 1989; Levy & Thompson, 2011). War was conducted on a large scale by ancient empires and over the centuries gradually made subject to certain rules.

Rule-based warfare requires numerous intersubjective understandings. By the nineteenth century, reinforcing feedback between understandings and rules had given rise to a highly differentiated European regional system in which states competed for standing primarily by means of warfare, and those recognized as great powers assumed certain responsibilities for maintenance of the system. In the next hundred years the system expanded to include non-Western and non-Christian political units and transformed itself into a global system. The definition of war and the rules governing it, initially European, are now effectively international. Modern war became an increasingly complex social practice (Levy & Thompson, 2011). It is based on the concept of the state: a sovereign political unit with a near monopoly over the use of force on its territory. It also requires a regional or international society which these political units have an interest in maintaining. The society legitimates actors through their collective recognition of their sovereignty by other actors and differentiates war from peace by means of legal definitions and associated practices (Wright, 1965). War was linked to sovereignty because it was defined in terms of actions that encroached on sovereignty (e.g., invasion, economic blockade). Such transgressions also provided justifications for declaring war against another state.

War conceived of in this way became a military contest fought for political goals, as Clausewitz (1976) famously recognizes. States use violence, he observed, to bend or break the will of an adversary, but its targets and modes of application are generally determined by rules or norms. This understanding and practice of war is modern because before the seventeenth century we cannot really speak of states or effectively distinguish between intra- and interstate violence.

War must accordingly be treated differently from violence, not merely as an extension of it as so many evolutionary studies do. It cannot readily be explained as an evolutionary adaptation. There is a consensus among scholars that interstate war—in contrast to intrastate violence—is on the decline. If we take a longer historical perspective, the frequency of war has been dropping throughout the modem era (Wright, 1965, pp. 121, 237, 242, 248, 638; Levy, 1993, pp. 139–144; Holsti, 1991). Each century since 1648 shows a decline and the decades since 1945 have been the most peaceful in recorded history in terms of the number of interstate wars and the per capita casualties they have produced (Holsti, 2005). Figure 1 below shows the number of ongoing interstate, colonial, and civil wars across the decades since 1945.

Evolution, Adaptation, and ImitationClick to view larger

Figure 1. Armed Conflicts (25+ Deaths pr. Year)

Human beings have remained relative stable in their genetic makeup over the last half-millennia, so we must look to features of their environment and their reflection about them to explain this decline (Levy & Thompson, 2011). Elsewhere (Lebow, 2010), I argue that the decline in the frequency of can be attributed to ideational change. Historically, the principal motives for war were status and honor, material interest, and security. Increasingly leaders came to believe that war was counterproductive to these goals, a process that began in the late eighteenth century with growing recognition that war interfered with trade and investment, both of which were engines of economic growth.

Evolutionary approaches to international relations are one-sided because they privilege nature over nurture. Pinker (2002, p. 127) suggests that it is a mistake to create a nature–nurture binary. We separate them out for purposes of analytical clarity, but this “contradicts the principles of dialectical understanding, which says the two are ‘ontologically coterminous’—not just in the trivial sense that no organism lives in a vacuum, but in the sense that they are inseparable in every aspect of their being.”4 Dunbar and Barrett (2007), editors of the Oxford Handbook of Evolutionary Psychology, insist that an evolutionary view “does not—and should not—commit us to any particular assumptions about the genetic determination of behavior.” Learning, “and by extension cultural transmission, play an especially important role in the behavior of humans” (also Low, 2012. The important question is how nature and nurture interact.

Unnatural Selection

Darwin and biologists who work in the evolutionary paradigm insist that natural selection requires reproduction and mortality. Neither condition exists in international relations. States do not reproduce and pass along genes, and most do not die. If a giraffe with a long neck can reach more leaves, it is more likely to survive and reproduce. Over multiple generations, the statistical average of giraffe neck lengths will increase, but not beyond the point where it is no longer functional. The modern state system has witnessed the death of some political units and the rise of others, but selection also requires offspring who inherit parental genes. This does not happen in international relations. At best, we use the concept metaphorically when we speak of successor states to former empires.

Many international relations scholars accordingly use evolution in a non-biological sense. They contend that the international system generates constraints and opportunities that reward certain behaviors or structures. Political units that develop these structures or display this behavior are more likely to survive and succeed.

“Unnatural selection” is central to Waltz’s (1979) theory of international politics. He argues that the international system selects for behavior that copes most effectively with anarchy and threats to survival arising from it. States that do not adapt “fall by the wayside,” producing a degree of behavioral uniformity (118). This selection process is absolutely essential to Waltz’s effort to construct a parsimonious theory of international relations at the systems level. It is only possible if selection pressures are strong enough to compel homology in surviving units, making them largely interchangeable. The only other condition that allows units to be treated as interchangeable is a system composed of so many units—like molecules in gases and cars in highway systems—that it is feasible to generalize from the norm. This does not work for international relations.

There is no empirical evidence to support Waltz’s assumption of system selection. The total number of states shrank in the nineteenth century due to Napoleon’s consolidation of the Holy Roman Empire, German and Italian unification, and colonial expansion. However, in the twentieth century, it increased from 57 in 1900 to 193, not counting Taiwan.5 Even in Europe, it grew, from 32 in 1945, to 43 today. Astute observers have noted that the international system is ordered in such a way to keep failed states alive, with consequences not always beneficial for their inhabitants (Rotberg, 2004). Moreover, a significant number of states that disappeared in the nineteenth and twentieth centuries did so voluntarily through unification, as in the case of the component units of modern Germany and Italy. Unnatural selection requires an unforgiving environment, but the survival and proliferation of states in the last century, and the survival of weak and dysfunctional ones, undercuts efforts by realists and liberals alike to apply this mechanism to international relations.

Waltz (1979, pp. 72–77) recognizes that relatively few states have been eliminated, but still expects the fear of it to have profound effects on leaders. They will hasten to imitate the behavior of their most successful competitors. Such mimicry, he maintains, brings about congruence in foreign policy behavior. Even if true—and there are many reasons to doubt his claim—this is not evidence of selection, but of the power of a different mechanism. If states do not “die” and leaders recognize this political truth, we would in any case expect to see the opposite of what Waltz predicts: more rather than less diversity in domestic structure and foreign policy behavior because leaders would be comparatively freer to respond to domestic pressures (Wilson, 2013).

Liberals offer their own variants of the unnatural selection. In The Rise of the Western World, North and Thomas (1973) contend that that the territorial state was the inevitable product of economic development and that this outcome was due to selection. Political scientists reject their claim. Ruggie (1993), Spruyt (1994), and Nexon (2009) note that when centralized territorial states began to emerge, many would-be territorial states failed while some city states, city leagues, and dynastic regimes grew and prospered. Like John Herz before them, Ruggie, Spruyt, and Nexon, among others, find political and legal developments more important (Herz, 1957; Tilly, 1975; Mann, 1986). Ruggie (1993) emphasizes the legitimacy that sovereignty conferred on territorial states. Spruyt (1994) directs our attention to the role of political coalitions and the superior ability of leaders of territorial states to form and maintain them as well as their ability to standardize weights, measures, coinage, and laws. Herz (1957), Spruyt (1994), and Nexon (2009) consider the success of the territorial state to have been a highly contingent and non-linear outcome. Spruyt (2001) cautions against a crude evolutionary approach that assumes convergence, as states are unlikely to adopt a single form but may pioneer diverse niches—and do so as a result of reflection and conscious policies.

A key assumption of the liberal paradigm is that liberal, capitalist democracy is the most efficient response to the modern world. Liberals often invoke unnatural selection to account for its proliferation. Some argue that domestic demands for wealth undermine states that are authoritarian, inward looking, kleptocratic, and dependent on import substitution. Others stress system-level pressures that are alleged to have the same effects (Gourevitch, 1978; Friedman, 1999; Solingen, 1999). The end of the Cold War and the so-called Arab Spring are offered in evidence, although neither appears in retrospect to have promoted democracy. Still other liberals employ the mechanisms of imitation and conscious adaptation. The latter involves changes in policy or structure motivated by the belief that they will make the state more efficient, profitable, or powerful (Rosecrance, 1986; Fukuyama, 1992; Solingen, 1999).

Imitation and conscious adaptation differ from natural and unnatural selection because they represent conscious choices by actors. Imitation and adaptation produce outcomes that may also reveal some degree of convergence, but as a matter of choice, not of selection. Imitation involves the copying of structures or practices of others, presumably because they are seen as successful or desirable for other reasons. Many eighteenth-century rulers copied Louis XIV in building palaces and gardens at great expense and no obvious benefit beyond their quest for standing (Blanning, 2007, pp. 423–425). As almost every continental leader acted this way, there was little relative gain.

Adaptation also involves choice, but not always copying. Leaders may strike out in directions of their own if they consider it politically, economically, or strategically advantageous. British encouragement of banking in the eighteenth century, German development of Blitzkrieg tactics on the eve of World War II, and Stalin’s five-year plan in the 1930s are cases in point. These strategies were novel and successful, at least in part, because they at odds with conventional practices.

When feasible, leaders tend to imitate the practices of successful states and avoid the problems of failed ones. To do so they must correctly identify the structures or practices that have led to success or failure as opposed to those that may be prominent but not critical. These structures and practices must also be susceptible to duplication; it would have been difficult, if not impossible, for France or Austria in the eighteenth century to raise private loans from local banks, for Britain or France in the eighteenth and nineteenth century to have spent the same proportion of their national income as Prussia on their armed forces, or for the Soviet Union to have adopted the kind of open society and encouragement of innovation that helped the US to pioneer the information revolution. Finally, leaders require the will and the authority to bring about needed changes in their domestic structure or domestic and foreign policies. These conditions are only infrequently met in the real world. The Meiji era Japan may one of the most prominent successful examples. However, imitation can involve unforeseen costs, as Zarakol (2011) has so perceptively demonstrated in the cases of Japan, Turkey, and Russia, and their efforts to become “Western.”

Imitation and conscious adaptation collapse into one mechanism if leaders imitate others because they believe their institutions or practices are the most rewarding. Successful adaptation only occurs when leaders’ choices end up conferring advantages. It is often difficult to distinguish between the two mechanisms or to determine their respective utility. Much imitation in politics, as in business, is counterproductive, so the most common structures and practices are not necessarily the most efficient, productive, or “best” with respect to the criteria in question. The so-called “Washington consensus,” forced on some states, and freely adopted by others, is a good case in point (Held, 2004). It brought about a degree of uniformity—at least for a while—that did not reflect system pressures but those emanating from one powerful state. The earlier similarity in political ideology and institutional structures of the Warsaw Pact offer a more extreme example of this phenomenon. When Soviet pressures ceased, communist regimes everywhere in Europe collapsed (Lévesque, 1997).

Scholars must not make the mistake of thinking that whatever convergence they observe is necessarily evidence of efficient adaptation and a better or best possible world. Even when regional or international environments promote convergence, other conditions work against it. Given the discrepancy in power in regional and international society, leading powers may be able to shape the environment in a way to minimize the constraints they face and maximize their opportunities (Rapkin, 2001). If several great powers combine toward this end, the effects may not be dissimilar to that of oligarchies in markets. Until the modern era, the reach of great powers did not extend much beyond their borders, and generally not fully within them. There was accordingly considerable variation in unit structures and political practices within and across regions. Territorial states have largely replaced other units, but it is by no means evident that this so-called globalization is producing the kind of uniformity in governments and practices that liberals expect. The United States and China may be telling cases. The US differs from most Western states in many ways (e.g., role of religion, capital punishment, gun ownership, anti-government sentiment, emphasis on unilateralism in foreign policy), and these differences may be growing rather than diminishing. China has become a major player in the world economy and in regional and international institutions. It has conformed to dominant practices in many ways, but not in others. Nor is there evidence that it will show greater homology with the West over time (Lampton, 2008; Ross & Feng, 2008; Halper, 2010; Foot & Walter, 2011).

Mechanisms Reconsidered

Evolution purports to explain morphological change. However, other theories and mechanisms are often necessary to link morphological change to behavior. Biologists are sensitive to this problem. They stress the complex ways in which inheritance and environment interact and devote increasing attention to the environmental triggers of genes. To date, evolutionary theories in international relations show little of biologists’ sophistication or caution.

In biology, evolution is a theory of process, not of structure. It offers a mechanism to help explain change, but says nothing about its contents. Evolution is a historical science and makes no predictions about the future beyond establishing an envelope within which change is possible (Scriven, 1978). Some international relations scholars deploy evolution in a purely historical sense. Others use it to make predictions. Liberals have a telos: the global triumph of capitalist democracy. For Darwin and contemporary evolutionary biologists teleology and evolution are incompatible. This should be true for any evolutionary theory that relies on selection—natural or unnatural—for its mechanism.

Scholars must specify whether they are using evolution in a biological or metaphorical way, and natural or unnatural selection as their mechanism. Natural selection focuses on genetic change. Its advocates argue that our nature has a significant, even determining, effect on how we behave. Unnatural selection argues by analogy to biological evolution. Those who invoke this mechanism contend that the environment in which political units operate generates powerful constraints and opportunities that promote isomorphism in structures and practices. Waltz (1979) relies on unnatural selection but also on conscious adaptation, without ever distinguishing between them. He also relies on imitation. He is not alone in using multiple mechanisms and failing to distinguish between or among them.

Many evolutionary studies engage in what Pinker (2002) describes with approval as “reverse engineering.” Thayer (2004), for example, assumes that the present world is the best of all worlds in the sense of species fitness. Theorists of this kind reject out of hand the idea that the social world is complex, contradictory, and difficult to characterize on the basis of a few simple assumptions or features. They rule out the possibility that the dominance of the territorial state, capitalism, and other prominent features of contemporary international relations are the product of multiple causes, confluence, chance, and agency—often interacting in non-linear ways. They ask only what human characteristics favor existing arrangements and what evolutionary processes—as opposed to cultural ones—could be responsible for them. This approach masks important normative assumptions and is circular in its application. Authors single out particular behavioral attributes or so-called tendencies because they are hostile to political and social change (e.g., equal treatment of women) or favor hardline “realist” foreign policies. This is evident in the writings of, among others, Wilson (2012), Pinker (2002), Hudson and den Borer (2012), Rosen (2007), Haidt (2012), and Thayer (2004).

Could the concept of evolution be applied in a more scientific way to history and politics? Ironically, the success of human evolution makes it less applicable to our species. A gene can be canalized so it helps to produce a specific phenotype. But at least as often, the gene requires a trigger that is environmental in nature. Our large brain is the product of this latter kind of phenotypic plasticity (Schaller, Park, & Kenrick, 2012). Thanks to our intelligence, our instincts have become correspondingly weaker, and we have more individual and collective choice about our behavior and our environment. Culture has replaced instinct in ways it has not for other animals. There is nevertheless a pronounced tendency among those who turn to evolutionary psychology to attribute more rather than less behavior to instinct.

Another major problem for evolutionary psychology is the gradual nature of evolution. It has real effects on human beings, but only in the long-term. We have been anatomically human for something over 100,000 years. Language ability, lighter skin color in populations that migrated to northern climates, and increased lactose tolerance are products of evolution. So too is the appeal of sugar and fat. For most of our existence we were hunter-gatherers and struggled to get enough food to survive. Today, the human proclivity to eat red meat, fatty foods, and sweets produces obesity, and it in turn is a major cause of disease and physical impairment. Evolutionary psychologists are probably right in arguing that what made us effective hunter-gatherers did not prepare us for life in modern societies.

If some of our proclivities are functional and others are not, it rules out the possibility that we live in the best of all worlds, or even the one best suited to our genetic makeup. Evolution is a path-dependent process that makes us creatures with tastes, habits, and other proclivities that developed over the millennia. Once we began traveling down a particular evolutionary path, it opened up new opportunities while closing down others. As our environment changes faster and more dramatically that we do genetically, we are never maximally functional in any environment, and it is therefore inappropriate to infer our “nature” from it.

The long-term character of biological change creates an acute problem for the application of evolution to international relations. Regional political systems, and more so, the global one, are very recent developments on an evolutionary scale. The modern European state system is conventionally accepted to have begun in 1648, but 1815 is arguably a more accurate starting point. The human race is basically the same today as it was then—or 1,000 years earlier. The best we can do in this circumstance is to invoke the concept of “exaptation,” coined by Gould (1982) to describe something that evolved in response to one kind of selective pressure but is now used for some other purpose by an organism. An often-cited example is bird feathers, which originally provided warmth but later made flight possible.

We are on shaky ground when we try to explain any kind of social behavior in evolutionary terms even when we restrict ourselves to the selection of individuals. Inherited characteristics rarely dictate specific behaviors. Social order offers a good example. Primate evolution may tell us something about its origins but not about its expression. Most species form families and larger kinship groups (Harcourtand, de Waal, 1992; de Waal, 1997; De Waal & Tyack, 2003). These include apes, our closest relatives in the animal kingdom. In monkeys and apes, social behaviors tend to be phylogenetically fixed, but each species still exhibits considerable variation. Individual chimpanzee and bonobo groups have unique combinations of tools and food gathering techniques. There is no evidence that they learn from one another, so reinvention of techniques is the most likely explanation for whatever duplication exists (Wrangham, McGrew, de Waal, & Heltne, 1994; de Waal & Ferrari, 2012).

Human cultures exhibit far greater diversity than chimps and bonobos. They run the gamut from wealthy to poor, extremely hierarchical to more egalitarian, from repressive towards women to more gender-neutral, from religious to secular—and these are only a few possible dimension of comparison. Social groups among great apes provide security for members of the community, especially the young, and cooperative behavior facilitates hunting, security, and child rearing. Human communities may have formed for the same reasons. That human beings may be genetically predisposed to social orders tells us little to nothing about the nature of their orders. To understand this variation we must turn to the physical conditions societies confront, the values they emphasize, and the choices they make. At best, evolution has determined the limits of what is possible, or put another way, the envelope in which humans and their societies are free to experiment and develop.

Evolutionary psychology contends that selection is the only known natural process that builds highly ordered and functional organization (Dawkins, 1976; Tooby & Cosmides, 2005). An alternative approach envisages social order, and complexity more generally, as an emergent property. As Conway Morris puts it: “First there were bacteria, now there is New York” (Lineweaver, Davies, & Rose, 2013). There is a consensus among scientists that complexity in the physical universe is increasing over time, but so is entropy—defined as the degree of disorder in a system. The two are compatible because order, not complexity, is the obverse of disorder. In the biological world complexity was a long time coming but then picked up markedly, perhaps exponentially (Morris, 2013). Morris believes biological systems are pushing the limits of complexity and hastens to point out that evolution is not a linear story. Great complexity led to the extinction of many species, while simplification for others led to success if measured in terms of survival and spread of range. There is a consensus among biologists that survival of the fittest is not necessarily “survival of the most complex” (Lineweaver, Davies, & Rose, 2013).

What about the social world? Orders have grown larger and more complex. They are more differentiated than in the past with many more institutions and roles and thicker rule packages for both. They require more knowledge to negotiate successfully. The greater complexity of modern societies, which is a product of and catalyst for economic and scientific development, enabled them to extend human longevity, banish famine, and eradicate or limit the effects of many infectious diseases. However, economic development puts societies at risk for other reasons. Nuclear weapons and global warming arguably have the potential to destroy much of the human race. As we become more dependent on information technology we also become more vulnerable to interference with its functioning. So too, has globalization linked us in ways that facilitate the spread of new pathogens.

Reflexivity is a fundamental human characteristic, making imitation and conscious adaptation the most powerful mechanisms in the social world. Both mechanisms can interfere with and work against selection at every level of social aggregation. As noted, European monarchs followed Louis XIV in building palaces and gardens like those of Versailles for reasons of status. They often came close to bankrupting their states in the process. In the nineteenth century, colonies and navies became the sine qua non of greatness. German pursuit of a blue water navy consumed a significant percentage of the country’s steel output and was the principal cause of otherwise avoidable Anglo-German hostility. In our era, the spread of neoliberal economic and financial practices, tobacco, gas-guzzling cars, beef consumption, and fast food restaurants are equally maladaptive. To what extent is the spread of diverse political, strategic, economic, and financial practices, domestically and internationally, the result of adaptation or imitation?

Adaptation and imitation are sometimes reinforcing but often cross-cutting. Colonies and nuclear weapons were pursued because they conferred high status, but strong arguments can be made that they proved maladaptive. One of the interesting and important questions for international relations scholars is what relevant actors thought they were doing at the time? Did they distinguish between imitation and adaptation? Did they think their imitative practices were adaptive or did they recognize that they brought status at high cost? I believe that we will discover that political actors, like ordinary people, convince themselves that they need not make tough choices. Leaders want to believe that the policies they prefer for whatever reasons will not only succeed but be beneficial, and certainly not damaging, to other goals. They are unlikely to distinguish imitation from adaptation because they are predisposed to see the former as consistent with the latter.

Not all practices—perhaps not even most—spread because they are beneficial. And not all widely adopted practices live up to their promises. Compare the dangerous consequences of tobacco addiction to the generally beneficial effects of coffee. Empirical evidence of convergence that was maladaptive would constitute a serious challenge not only to evolutionary approaches to international relations, political economy, and domestic politics, but also to realism, liberalism, and rationalist accounts of war. Realism would take a big hit if big defense budgets could be shown to have been counterproductive during the Cold War and again in the post-Cold War world (Lebow & Stein, 1994).

International relations theories confront the opposite problem of evolutionary psychology, which leaves no doubt about its mechanism. The problem is that this mechanism is indeterminate when it comes to behavior. International relations theories, by contrast, do a poor job of identifying their mechanisms. Those that rely on evolution frequently fail to distinguish between evolution as a biological process and a metaphor. They often confuse unnatural selection with conscious adaptation and imitation. Sometimes they use the word evolution as a synonym for change and offer non-evolutionary accounts for it. The otherwise excellent Levy and Thompson (2011) study of war is a case in point. The authors talk about evolution but rely overwhelmingly on adaptation and imitation. We can develop more sophisticated understandings of change and convergence by being more explicit about the mechanisms we hold responsible for them. The most important lesson for international relations theory is the need to focus more on mechanisms. We need to define them more carefully, specify how they work, and do extensive empirical work to limit the circumstances in which they do.


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(1.) For this debate see Mameli (2012). On niche construction and the problems it creates for evolutionary psychology see Odling-Smee, Laland, and Feldman (2003), Laland (2006).

(2.) For an overview, Wilson (2012).

(3.) The larger controversy surrounding Chagnon concerns false allegations that he invented much of what he relates and spread disease among the tribe (Eakin, 2013).

(4.) This echoes the observation of geneticist Dobzhansky (1962, pp. 73–74) that human evolution is the “interaction of biology and culture.”

(5.) Between 1860 and 1895, some 80 countries were erased from the map. The Risorgimento in Italy abolished four dukedoms and one small kingdom; German unification eliminated 37 small-to-medium-sized kingdoms and principalities; and European colonial expansion did away with, or converted into “protectorates,” three Central Asian khanates, some 25 African states, four Pacific island kingdoms, six Southeast Asian monarchies, and numerous smaller tribal associations. By the mid-1890s the total number of independent countries had dropped to 24 in Europe, to five in Asia, and to only two in Africa. At the time of Queen Victoria’s Diamond Jubilee ceremony in 1897, just after the curtain went down on the monarchies of Hawaii, Tonga, Madagascar, Aceh, and Sulu, there were 56 independent countries. This was an all-time low in the modern era.