A Recent Invention?

Some have argued that deliberation is a cultural invention originating in the Western Enlightenment period (see the discussion in Min Reference Min2009). Deliberation, then, would presumably have little to do with the nature of our species. Yet, the argument that it is a recent Western invention seems increasingly implausible in light of the accumulating evidence of its occurrence in disparate contexts and cultures in world history (Sass Reference Sass, Bächtiger, Dryzek, Mansbridge and Warren2018). Examples of deliberation range from the ancient Athens of Pericles (Elster Reference Elster and Elster1998) to Indian ‘Buddhist, Jain, and Hindu traditions as early as the fifth century BCE’ (Parthasarathy and Rao Reference Parthasarathy, Rao, Bächtiger, Dryzek, Mansbridge and Warren2018, 806–807), to the ‘consultative and deliberative traditions [in China that] go back thousands of years’ (He Reference He2014, 66). Importantly, deliberation appears to have occurred – to varying degrees – in diverse cultures prior to Western colonization and the Enlightenment (Gagnon et al. Reference Gagnon2021; Sen Reference Sen2003). This makes it unlikely that its cross-cultural observation is solely the result of the diffusion of a Western practice (cf. Tooby and Cosmides Reference Tooby, Cosmides, Barkow, Cosmides and Tooby1992).

The empirical documentation of deliberation in hunter-gatherer societies of the late nineteenth and early twentieth century casts further doubt on the idea that deliberation is a recent cultural practice (for details, see van der Does Reference van der Does2024). Experts generally consider life in these small-scale, hunter-gatherer societies the closest available approximation of ancestral life defining humanity until some twelve thousand years ago (Tooby and Cosmides Reference Tooby, Cosmides, Barkow, Cosmides and Tooby1992; Marlowe Reference Marlowe2005; Van Vugt, Hogan, and Kaiser Reference Van Vugt, Hogan and Kaiser2008). Empirical traces of deliberation occurring in hunter-gatherer societies in different parts of the world – from the Aranda in Australia (Spencer and Gillen Reference Spencer and Gillen1927) to the Mbuti in the Congolese Ituri forest (Turnbull Reference Turnbull1962; Turnbull Reference Turnbull1965) to the Comanche in North America (Wallace and Hoebel Reference Wallace and Hoebel1952) – thereby make it conceivable that deliberation has deep roots in our species’ history. A more plausible explanation of its apparent universality than cultural diffusion, hence, is that deliberation reflects a shared human nature that can be retraced to a common ancestor.

Human Nature and Evolution

There is an emerging consensus in the social behavioural sciences that inquiries into human nature should derive from our understanding of human evolution, specifically the evolution of the human brain (Scott-Phillips, Dickins, and West Reference Scott-Phillips, Dickins and West2011). From this perspective, ‘human nature’ consists of three products of evolution: adaptations, byproducts, and noise (Barkow Reference Barkow and Barkow2006; Goetz and Shackelford Reference Goetz and Shackelford2006).

In relation to the human brain, adaptations amount to psychological mechanisms that evolved because they improved the odds of survival and/or reproduction of humans who lived as (semi-)nomadic hunter-gatherers during the long stretch of our species’ evolutionary past between 250 and twelve thousand years ago (Cosmides, Tooby, and Barkow Reference Cosmides, Tooby, Barkow, Barkow, Cosmides and Tooby1992; Lewis et al. Reference Lewis2017; Scott-Phillips, Dickins, and West Reference Scott-Phillips, Dickins and West2011; Van Vugt, Hogan, and Kaiser Reference Van Vugt, Hogan and Kaiser2008). These mechanisms only trigger specific cognitive, physiological, emotional and, ultimately, behavioural responses when they detect the specific kind of environmental input that would have made those responses effective in solving adaptive problems; that is, recurrent problems impinging on the survival and/or reproduction of our distant ancestors (Cosmides, Tooby, and Barkow Reference Cosmides, Tooby, Barkow, Barkow, Cosmides and Tooby1992; Pietraszewski and Wertz Reference Pietraszewski and Wertz2022; Tooby and Cosmides Reference Tooby, Cosmides and Hogh-Olesen2010). Recent research suggests that evolution has equipped the human brain with a suite of politically relevant psychological mechanisms (DeScioli and Bokemper Reference DeScioli and Bokemper2019; Lopez and McDermott Reference Lopez and McDermott2012; Petersen Reference Petersen2015; Von Rueden and Van Vugt Reference Von Rueden and Van Vugt2015). For example, people seem to share an evolved mechanism that makes them quick to single out individuals who do not reciprocate in social exchanges; makes them inclined to become angry upon the detection of such cheaters; and motivates them to broadcast acts of cheating and to avoid sharing with cheaters (Bøggild, Aarøe, and Petersen Reference Bøggild, Aarøe and Petersen2021; Cosmides Reference Cosmides1989; Cosmides and Tooby Reference Cosmides, Tooby, Barkow, Cosmides and Tooby1992; Cosmides and Tooby Reference Cosmides and Tooby2013; Petersen et al. Reference Petersen2012).

Note, then, that it makes little sense from an evolutionary perspective that our human brain would be pre-programmed (read: adapted) to motivate us to refrain from deliberation (or any other social behaviour) unconditionally. To return to the example of warfare, it seems improbable that an incessant urge for (no) warfare would have promoted our ancestors’ chances to survive. As Boyer (Reference Boyer2018, 58) indicates in his review of the relevant literature: ‘What makes humans go to war or cooperate is not stable, general, and context-free preferences for aggression or for peace, as Hobbesians and Rousseauists believed, but a set of conditional mechanisms that weigh the value of either strategy, given the current environment.’ It follows that unconditional statements about human nature and deliberation – like the contention of deliberation’s most fervent critics that people, by nature, are invariably averse to respectful, reason-based political discussion (Achen and Bartels Reference Achen and Bartels2016, 301–302) – do not accord with evolutionary theory.

Byproducts refer to ‘concomitants or side effects of adaptations […] that did not evolve to solve an adaptive problem’ and, hence, did not result in a specialized psychological mechanism (Al-Shawaf et al. Reference Al-Shawaf and Shackelford2020). For example, in the context of religion, some have argued that ‘beliefs about supernatural agents seem to emerge readily and spontaneously’ not because that solved an adaptive problem among our distant ancestors but because people share evolved psychological mechanisms to (overly) quickly detect agents and ascribe goals and motives to those agents (Kirkpatrick Reference Kirkpatrick2011, 332). Noise refers to a variety of random effects, amounting to a ‘variation in the structure and function of adaptations or byproducts that [were] not selected for and did not evolve for any specific reason’ (Al-Shawaf et al. Reference Al-Shawaf and Shackelford2020). The next section applies this discussion on evolution’s three products (that is, noise, byproducts, and adaptations) to deliberation.

Noise, Byproduct, or Adaptation?

A ‘deliberation-as-noise’ hypothesis would hold that deliberation qualifies as a random effect and, hence, lacks any signs of special design (Buss et al. Reference Buss1998; Williams Reference Williams1966). It can thereby function as the null hypothesis that deliberation is in no way a product of natural selection; that is, neither an adaptation nor a byproduct (Al-Shawaf et al. Reference Al-Shawaf and Shackelford2020). What speaks against this hypothesis is deliberation’s complexity. Understood as interpersonal verbal communication involving mutual respect and reasoning about (potential) political decisions ^{Footnote 2} (cf. Bächtiger and Parkinson Reference Bächtiger and Parkinson2019, 21), deliberation’s behavioural complexity seems indicative of an equally complex psychological apparatus that is unlikely to be the result of mere chance (Cosmides et al. Reference Cosmides, Tooby, Barkow, Barkow, Cosmides and Tooby1992, 9). What is more, there exist plausible alternative hypotheses that deliberation is a product of natural selection, to which I turn next.

A ‘deliberation-as-byproduct’ hypothesis would hold that deliberation is not itself an adaptation but ‘emerged as a byproduct of another adaptation’ (Al-Shawaf et al. Reference Al-Shawaf and Shackelford2020). One plausible candidate is that deliberation is a byproduct of reasoning. The ‘argumentative theory of reasoning’ (Mercier and Sperber Reference Mercier2011, Reference Mercier and Sperber2017) holds that reasoning evolved for a social purpose: ‘to find and evaluate arguments so as to convince others and be convinced when it is appropriate’ (Mercier and Landemore Reference Mercier and Landemore2012, 248). More specifically, reasoning formed an adaptive response to the problem that language allows for lying and deceit, threatening the efficient communication and cooperation language otherwise allows for. As this only presents a problem when people do not already agree, the relevant environmental input that should trigger reasoning is ‘disagreement between at least two individuals in the course of a conversation’ (Mercier and Landemore Reference Mercier and Landemore2012, 248).

Following this theory, we could hypothesize that deliberation constitutes a universal human behaviour because people (a) are adapted to exchange arguments when faced with disagreements and (b) regularly find themselves in discussions over politics where sociocultural constraints complicate social dominance and thereby require them to treat each other as equals. This accords with evidence of deliberation occurring regularly in contexts where cultural norms of egalitarianism are in place, such as in small-scale hunter-gatherer societies (Gintis et al. Reference Gintis, Van Schaik and Boehm2015; van der Does Reference van der Does2024) or social movements (Min Reference Min2015; Polletta Reference Polletta2002), as well as with evidence of deliberation being prevalent where rules on turn-taking and, for example, norms of ‘self-depreciation’ complicate the domination of political discussions, such as in town hall meetings and various small-scale societies (Boehm Reference Boehm1996; Cossart et al. Reference Cossart, Felicetti and Kloppenberg2019; Liberman Reference Liberman1980; Mansbridge Reference Mansbridge1983).

Such a byproduct hypothesis hinges on the idea that deliberation ‘does not appear to exhibit evidence of special design for solving an adaptive problem’ (Al-Shawaf et al. Reference Al-Shawaf and Shackelford2020). A ‘deliberation-as-adaptation’ hypothesis would hold instead that it did solve an adaptive problem in the environment of our common ancestors, ultimately resulting in an evolved psychological mechanism specialized in addressing that respective problem. One possibility is what I will call the ‘ingroup hypothesis’ of deliberation (for details, see van der Does Reference van der Does2024). It holds that deliberation evolved as an effective solution to a problem recurrently faced by our hunter-gatherer ancestors: disagreement over upcoming political decisions with other members of one’s group. This problem would have threatened group cohesion and thereby the cooperative efforts required for both group and individual survival (cf. de Waal-Andrews and van Vugt Reference de Waal-Andrews and Van Vugt2020). Per the ingroup hypothesis, deliberation formed a solution to this problem because it cushioned the threat to group cohesion via respectful discussion, increasing the odds of finding common ground and signalling individuals’ worth to the group. As this could have introduced the kind of conformity that would have led to empirically inaccurate decisions (Brennan Reference Brennan2016), swapping one type of threat to survival (that is, the group falling apart) for another (that is, making the wrong decision), political discussion would have had to involve reasoning too, enhancing rather than undermining the group’s collective intelligence.

This leads to the expectation that people share a specialized mechanism summarized in the heuristic ‘IF I disagree with someone from my ingroup about an upcoming political decision, THEN deliberate.’ In line with such a heuristic, there is evidence that deliberation is particularly likely when people disagree about political decisions but share strong social bonds (Myers Reference Myers2022; Niemeyer et al., Reference Niemeyer2024), such as within political parties (Wolkenstein, Reference Wolkenstein2018; Steiner and Dorff Reference Steiner and Dorff1980), congregations (Djupe and Olson Reference Djupe and Olson2013; Wood and Bloch Reference Wood and Bloch1995), or work teams (Mansbridge Reference Mansbridge1983). It also accords with evidence of deliberation subsiding when strong social bonds break down, societies become more divided, or affective polarization increases (della Porta 2013; Dryzek Reference Dryzek2005; O’Flynn Reference O’Flynn2006; Polletta Reference Polletta2002; Strickler Reference Strickler2018).

These initial byproduct and adaptation hypotheses lead to testable expectations. The byproduct hypothesis would expect deliberation to be triggered by any disagreement in contexts constraining discursive dominance. Furthermore, it suggests that the respectful, argumentative communication characteristic of deliberation does not rely on any mechanism specialized to address political problems and, hence, that we should observe such communication in response to the same environmental inputs in politically and non-politically oriented discussions alike. By contrast, the adaptation hypothesis would expect it to be triggered specifically by disagreements among ingroup members over political decisions.

To adjudicate between the two hypotheses, future work could start by testing to what degree people are inclined to deliberate when they converse together in political and non-political situations of ingroup disagreement, much like prior experiments have tried to tease out whether psychological mechanisms respond to socio-political problems specifically (Bøggild Reference Bøggild2020; Cosmides Reference Cosmides1989). Furthermore, as the adaptation hypothesis holds that political disagreement among people from one’s own group was the relevant environmental input for triggering deliberation in an ancestral environment lacking clear power differentials (van der Does Reference van der Does2024), future work could test to what degree people tend to be inclined to deliberate in response to ingroup political disagreements even when the situation allows for discursive dominance (contra the byproduct-of-reasoning hypothesis).

Concluding Remarks

How we think about human nature has profound effects on how we try to change human behaviour – and deliberation is no exception to that rule (John et al. Reference John2011). If we think that people are naturally predisposed to refrain from deliberation, we might try to convince policymakers that expensive projects to stimulate deliberation will not be worthwhile. If we think that deliberation is only triggered when specific rules or norms are in place, we might argue for strict moderation of town hall discussions, work team meetings, and, say, citizens’ assemblies. And if we think instead that people are, by nature, inclined to deliberate under certain conditions, we might argue that they should be left alone once those conditions are in place, as detailed instructions and careful facilitation cost time and energy and might also be unduly paternalistic. It follows that, for those interested in the questions of whether and how we should enhance deliberation in today’s societies, it is key to have an informed understanding of human nature.

In this article, I have argued that it is plausible that, one way or another, deliberation reflects a shared human nature; that we can only come to grips with this by engaging with the evolutionary sciences; and that we can formulate plausible hypotheses about humans’ evolved psychology, which expect deliberation to be triggered by the environmental inputs that would have triggered it, too, among our distant ancestors who lived in small-scale, hunter-gatherer societies. Much of the current pessimism about human nature and deliberation thereby seems unwarranted. Against deliberation’s critics, evolutionary theory makes it clear that unconditional statements about human nature and deliberation seem dubious. Against many of deliberation’s enthusiasts, hypotheses grounded in evolutionary theory suggest that deliberation might require little special instruction or facilitation (cf. Mercier Reference Mercier2011 on argumentation), and can be triggered quite spontaneously when people disagree and face constraints on discursive domination (the byproduct-of-reasoning hypothesis) or simply when they disagree about a political decision with people from their ingroup (the ingroup hypothesis).

My hope is that this will provide sufficient pointers for starting a research programme on the evolutionary psychology of deliberation. Not only will such a programme allow scholars of deliberation to move beyond sheer philosophical speculation about human nature (cf. Alford and Hibbing Reference Alford and Hibbing2004), it also holds the promise of integrating existing explanations of the conditions (un)favourable to deliberation (Farrell, Mercier, and Schwartzberg Reference Farrell, Mercier and Schwartzberg2023; Sass and Dryzek Reference Sass and Dryzek2014; Thompson Reference Thompson2008, 499–500) by providing an underlying theory as to why some conditions trigger deliberation and others do not (cf. Mercier and Landemore Reference Mercier and Landemore2012). Such insights into the psychology of deliberation will inevitably also improve our understanding of how it functions, as ‘we become better able to understand how something works when we know why it exists’ (Bøggild and Petersen Reference Bøggild, Petersen, Shackelford and Hansen2016, 253).