Selection is one of the three key mechanisms of evolution, alongside variation and replication (Mayr, 2002). When thinking about evolution in Darwinian terms, it comes naturally to see selection as confined to the biological world, where only the 'fittest' individual organisms successfully replicate and spread their genes to their offspring. However, evolution need not be confined to a single organism: ecologists have shown that groups can function as an adaptive unit, in which selection does not go to the advantage of the individual but works 'for the good of the group' (Nowak et al., 2010). However, for individuals to successfully cooperate, they must do something for each other, meaning that selection must be acting not only at the individual level but also at the group one.
Darwin (1871: 166) recognised as much in his The Descent of Man, when he wrote:
It must not be forgotten that although a high standard of morality gives but a slight or no advantage to each individual man and his children over the other men of the same tribe. . . an increase in the number of well-endowed men and an advancement in the standard of morality will certainly give an immense advantage to one tribe over another.
Darwin’s message here was actually two-fold. The first one can be easily taken at face value: we know that having a 'high standard of morality', i.e. being altruistic, gives the individual little to no advantage over other people. However, when several individuals abide by the same high standards of morality, cooperation is more likely to take place, which in turn helps the group survive. Hence, cooperation lies at the heart of group survival, as was discussed elsewhere on this platform.
The second message took over a century to unfold since the publication of the Descent of Man. Evolution needs not solely apply to the biological world. Over the past fifty years, several scholars from a wide range of disciplines have shown how the Darwinian building blocks can be employed to understand the evolution of culture (Cavalli-Sforza & Feldman, 1981; Boyd & Richerson, 2005; Richerson & Boyd, 2005), sociality (Wilson 2000 , 2013, 2019), religion (Wilson, 2003; Norenzayan, 2013), morality (Haidt, 2012), public policy (John, 2013; Atkins et al., 2019), and even economic (Hodgson & Knudsen, 2010) and political (Tang, 2011) institutions. In such cases, genes are not the element mutating, being selected on and replicating, but a similar mechanism is always in action nonetheless. As such, new customs, new rules, new rituals or new norms emerge and are replicated over time.
At the heart of many of these works lies the idea of multilevel selection: that selfish individuals might out-compete altruists within a group, but internally altruistic people outcompete selfish groups (Wilson & Wilson, 2007, 2008). But in order to do so, a pre-existing glue must be present that allows the group to cooperate. In their study of bees, Nowak et al. (2010) call them ‘pre-adaptive traits’: for humans, these can be selective markers such as language, religion, or ethnicity, all of which have traits that can mutate, be selected on, and replicate – either to future generations or to other groups.
Turchin (2003, 2005, 2015) takes this to the extreme by asking: what if multilevel selection can also explain the rise and fall of empires? That is, what if warfare – rather than nature – selects on and helps replicate traits across states to form new ‘organisms’, the empires?
Peter Turchin is an ecologist by training who has spent the past twenty years attempting to adapt multilevel selection theory to warfare. In his opinion, qualitative historiography is lacking in that there is no general theory that explains not just why this or that empire rose or fell, but why empires rise and fall in general. Multilevel selection, he claims, holds the key to explaining what he calls ‘historical dynamics’ (also known as Cliodynamics – from Clio, the Muse of History), or the competition and conflict between groups over time, some of which – the empires – dominate others (Turchin, 2005: 5).
At the heart of his thesis lie two key ideas. The first one is the notion of asabiya, an Islamic word which refers to the capacity of social groups for concerted collective action (Turchin, 2005: 6). This is because not all groups are able to act cooperatively to the same degree. Therefore, even if from a mathematical point of view multilevel selection sees groups of cooperators always outcompete groups of defectors (see below), the degree to which they are able to do so depends on the glue that binds them: what makes groups cooperate? In some cases it is religion (e.g. the crusades), in others it is ethnicity (e.g. the Rwandan conflict), in some more it is a political ideology (e.g. the Korean conflict). Depending on how strong their glue is, groups will successfully cooperate to varying degrees.
The second key idea is that of creative destruction. Warfare is obviously a brutal affair. It leaves behind a trail of corpses, destruction and desperation. Turchin does not shy away from its ugliness. Yet, he still recognises warfare as the yin to cooperation’s yang. This is because, from a multilevel section perspective, warfare has a creative side: by eliminating poorly coordinated, uncooperative and dysfunctional states from evolutionary contention, it can create new ones that are more likely to value cooperation, pacificism and affluence, thus creating societies that are even more just (Turchin, 2015: 41).
However, one still needs to differentiate creative conflict from conflict that is purely destructive. Multilevel selection can help in this regard, and to understand how it works, it is helpful to introduce a quick mathematical formula, adapted from George Price’s equation of natural selection, which describes how a particular trait changes frequency (i.e. spreads) over time (see Price, 1970; for a thorough review on the topic, see Frank, 2012).
In Turchin’s formulation, the Price equation adapted to warfare is:
This simple formula helps understand what happens to the overall frequency of cooperators in a group in a situation of competition. Remember that selection acts on two levels: selfish individuals may have an advantage over altruistic individuals in the same group, but altruistic groups outcompete selfish groups. “Selection strength on individuals” measures the disadvantage of individuals being cooperators vis-à-vis other selfish individuals within the same group. “Selection strength on groups” instead is a measure of how much being a group made up mostly of selfish individuals becomes a disadvantage in competition vis-à-vis other groups. What matters is not their absolute values, but the ratio of these selection strengths: the lower the cooperator disadvantage within the group with respect to defectors, and the greater the effect of cooperators on the group’s probability of survival, then the more likely it is that cooperation will spread, leading the group to survive (Turchin, 2015: 77).
Warfare behaves following the same logic: just as between-group competition nurtures cooperation and within-group competition destroys it, external war (war between societies) tends to be a force of destructive creation, and internal war (war within societies) tends to be merely destructive (Turchin, 2015: 104). However, Turchin adds a further caveat. Whether war is external or internal is only the first step. To act as a force of selection, warfare must not be inconclusive, i.e. it must result in some cultural traits out-competing others.
This is the case particularly for empires, which force the losers of a conflict to assimilate the winners’ culture, religion, social norms and institutions, or language. It can no doubt be quite traumatic for the losers, but it can also happen more gradually and in a mostly voluntary way, such as was the case for Roman Gaul, where the Celtic language was superseded by the more prestigious Latin.
This logic can then be expanded over time to explain the rise of empires (Turchin also suggests that lack of cooperation is what leads to empires falling, or what he calls ‘imperiopathosis’, see Turchin, 2005. For reasons of space, only the rise of empires has been treated here). Turchin et al. (2013) test a model to explain the rise of costly institutions that allowed large human groups to function without splitting up, such as the apparatus necessary to sustain an empire. They posit that the rise of these institutions was the result of intense competition between societies, carried out primarily by warfare, which in turn depended on the spread of military technologies. In addition, they suggest that those societies that originate on fault-line frontiers (e.g. Mesopotamia) are more likely to foster collective action because they have higher levels of asabiya, and it is here that most empires should originate (see Turchin, 2005).
They find that, between 1500 BCE and 1500 CE, their model could explain up to 65% of the variance in institutional evolution and predicted the actual pattern of spread of large-scale societies with uncanny accuracy. Put more simply, empires did rise where warfare intensity was highest, which is at fault-line frontiers, and warfare intensity was high because of strong between-group competition, which advantaged those societies where individuals successfully cooperated.
To sum up, Turchin’s argument boils down to a simple, generalisable explanation: rampant warfare leads to intense selection for larger society size, such as empires. But cooperation does not merely arise and it must be nurtured in the form of asabiya. To paraphrase a pioneering geneticist, if nothing in biology makes sense except in the light of evolution, to Turchin and other cliodynamicists nothing in history makes sense except in the light of cultural evolution.
We are who we are today as societies not because we as individuals are the ‘fittest’ from an evolutionary standpoint. Rather, it is because our ancestors’ groups were those that best exploited the multilevel structure of natural, but most importantly cultural, selection. Despite the everyday brutality and the seemingly never-ending conflicts, we managed to build up large-scale social norms and institutions that severely limited between-group conflicts, and instead nurtured cooperation to levels never seen in the past hundred thousand years.
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