Sharing in an unequal world: The origins and survival of human cooperation

The Pleistocene Social Contract: Culture and Cooperation in Human Evolution, by Kim Sterelny, Oxford University Press, 2021, 200 pp., $74.00 (Hardcover), ISBN 9780197531389

We live in dramatically unequal social worlds. A disproportionate amount of power and wealth is concentrated in the hands of small elites, who monopolize the economy, state apparatus, and access to decision-making. Yet, elites are massively outnumbered. This state of affairs appears even more puzzling if it’s true that we lived in egalitarian cooperative communities for the vast majority of our species’ evolutionary history and we had similar power and access to goods. If nonhierarchical contexts are ancient in our lineage – existing far before the emergence of our species – and cooperation played an important role early in the Homo lineage, then how did inequality originate and stabilize? And crucially, how does cooperation thrive in an unequal world?

Kim Sterelny’s Pleistocene Social Contract tackles these and other questions by taking us on an evolutionary journey through the facets and challenges of hominin cooperation, made more profitable and stable by the growing impact of culture.

Few philosophers have dared engage in building detailed, empirically constrained and explanatory scenarios of transitions in human evolutionary history. Over the last two decades, Sterelny has taken up this challenge and turned it into his philosophical signature. The Pleistocene Social Contract is yet another powerful example of Sterelny’s command of results from an impressive range of disciplinary fields – ethnography, paleoanthropology, archaeology, cognitive science, among others – and ability to knit them together into a sophisticated and coherent evolutionary framework.

In what follows, I will provide an overview of the structure and key claims of the book, before switching to a more critical discussion.

The Pleistocene Social Contract builds on the evolution of human social life and cognition earlier developed in The Evolved Apprentice (2012), and puts more flesh on the bones of his previous account of late Pleistocene transformations in a 200 pages-long read. The book advances an account of the coevolutionary loop between Homo sapiens’ dependence on cooperation and dependence on culture. In Sterelny’s view, it is this positive feedback loop, originating from initially small divergences from great ape lifeways, that has taken us on a different evolutionary trajectory:

We have become more culture-dependent as our cooperation has become more pervasive, and as the imprint of culture has increased, we have become more cooperative. Hominins are both extremely cooperative primates and encultured primates. (p. 12)

Specifically, the book is about the role of hominin culture in solving two crucial puzzles in the evolution of cooperation (Calcott, 2008): how cooperation originates from a noncooperative context and why it is profitable (the generation-of-benefit problem), and how further cooperation is incentivized and maintained in the face of free-riding individuals (the distribution-of-benefit problem). I will tackle them in order.

Among the fundamental intuitions inherited from The Evolved Apprentice and which the Pleistocene Social Contract’s account of the role of culture draws on, one crucial claim is that cumulative cultural evolution becomes important early but needn’t depend on a specific cognitive adaptation. This involves claims both about the nature of cultural inheritance itself, and on the particulars of human evolution. For instance, Sterelny points out that no smooth and incremental upward trend is apparent from the Pleistocene archaeological record, as innovations appear and disappear, sometimes stabilize, and sometimes reverse – not a pattern we’d expect if we had a single, special purpose cognitive breakthrough (see also Meneganzin & Currie, 2022). Adaptive support (genetic, cognitive, cultural) would have arisen later in environments in which cultural learning was already playing an important role. A second claim is that cumulative culture does not all boil down to high fidelity transmission, as this is crucial for only one form of cumulative culture (incremental improvement of an existing capacity through imitation learning). Sterelny adopts a broader conception of cumulative culture, as the ability to acquire capacities outside the so-called Zone of Latent Solutions (ZLS) – Tomasello’s and Tennie’s metaphor for describing skills potentially within the reach of individual learning and to which great apes are confined (Tennie et al., 2009). Cumulative cultural learning can be also achieved by attending to the products of skilled action (emulation learning) in structured learning niches, where artifacts serve as templates.

Thus conceived, cultural learning started to be increasingly important as it became essential to the foraging of high-value targets. This new evolutionary dynamic might have been ignited by the erectines’ demanding lifeways, with their complex Acheulean technology, expansion out of Africa, hunting and probably domestication of fire, even if cultural learning was still relatively narrow in bandwidth. Progressively, through the vagaries of social transmission in the Middle Stone Age (300-50kya) and risks of loss of informational capital, late Pleistocene foragers would have stabilized capacities for cumulative social learning comparable to ethnographically known forager populations. So much for the establishment and evolution of the material benefits of information sharing. But what about their distribution in light of the destabilizing threats posed by free-riders and bullies?

Sterelny charts the evolution of human cooperation as a four-phase model, that serves as the backbone of the core proposal of the book. We could think of each phase as re-proposing the origin problem – how a new form of cooperation is established – and the stabilization problem – how cooperation is maintained and incentivized in the face of new pitfalls. But be warned: each step in Sterelny’s long narrative is supported by empirical and theoretical backing, to whose details this short review can’t do full justice.

The first transition involves the suppression of ape-like male dominance hierarchy, taking place among early H. erectus up to the evolution of H. heidelbergensis (1.8 Ma − 800kya). This would have seen the establishment – initially in partial and unstable ways – of relatively egalitarian social bands, characterized by immediate return mutualism. In Sterelny’s view ambush hunting has played a crucial role in this transition, as it requires greater impulse control in a weaponized context, and profits of the kill are generated immediately and divided on the spot, making it easier to detect cheaters.

A second phase sees the shift in the foraging economy between immediate return mutualism to one in which indirect reciprocation became increasingly important (that is, contributions to someone else’s welfare being later rewarded by those not directly helped). This shift, taking place between roughly 120–50 kya, would have demanded new cultural and cognitive tools. Among these, projectile weaponry would have enabled small parties or even individuals to stand chances in stalk or ambush hunting, and gossip would have become fundamental to track fair dealing and good repute in increasingly complex systems. Sterelny argues that while for the suppression of dominance male hierarchy simple cognitive and motivational mechanisms sufficed, internalized norms became important for reciprocation in the late Pleistocene. And they would have helped reduce ambiguity in the distribution of profits, handle disagreement in broader groups, as well as mobilize third-party support to sanction against cheating. The transmission and reinforcement of norms is linked to the late Pleistocene expansion of ritual and material symbols, evidencing increased social stress and tension.

A third phase is marked by an expansion of the social and spatial scale of cooperation, involving cooperation between bands. This shift, which likely started as passive tolerance between bands and evolved into increasingly active and high-cost forms of cooperation, probably began with H. heidelbergensis but became complete only late in the Pleistocene. This would have been promoted by changes in foraging, with a transition to the ecological niche of an apex predator with more meat-based diets. But while community-level cooperation is advantageous to the solution of complex collective action problems – large-scale ecological engineering or organized violence – it poses novel coordination and logistic problems. Investment in corporate identity and loyalty becomes crucial to keep track of a richer set of kinship ties. These complex communities, sharing norms, rituals and myths and actively cooperating would have managed risk better in more hostile environments.

The final phase has received the most attention in the literature, that is cooperation in sedentary societies that have reestablished hierarchies, beginning toward the end of the Pleistocene/early Holocene. Although the Neolithic ‘Revolution’ (ca. 12 kya) was much more spread in time and space than previously supposed and certainly not a package deal, it introduced important changes. Among these, Sterelny lists a sedentary society, a farming and/or herding economy, a steep increase in demographic scale and complex but unequal social worlds. Storage foraging and farming generated surplus, a large fraction of which was taken by elites. Nonetheless, the social contract survived, and cooperation even expanded. This is described as deeply paradoxical. As egalitarianism eroded with the recognition and inheritance of private property, coercion of labor, increased opportunities for intercommunal violence and the rise of Big Men and prestige hierarchies, strategies were co-opted to legitimate inequality. Religion, ritual and ideologies played that role, partly persuading, partly coercing.

Addressing all the fascinating facets of Sterelny’s picture deserving of further discussion is an arduous task. I will start with a methodological note before pointing to a few areas that put pressure or elaborate on aspects of his account.

First, narratives are delicate tools. They both have a contentious philosophical reputation – being mistaken for idle speculations or just-so-stories is a looming risk (but see Currie & Sterelny, 2017) – and discussions abound on the extent to which they qualify as legitimate philosophy of science. Sterelny’s work superbly dismantles both those complaints. For (i) the degree of empirical detail and complexity of the Pleistocene Social Contract doesn’t undermine its coherence (we all have experience of how incredibly hard to build are complex and empirically grounded lies). The narrative predicts patterns in the traces left by our ancestors and is not immune to future discovery: it’s vulnerable, detailed, complex, risky. Not the kind of business just-so-stories are really into. (ii) Sterelny rips a classic philosophical question – how a recognizably human lifeway came to be – off from classic philosophical treatment. But by abandoning disciplinary compartmentalization, he’s not abandoning philosophy: his approach is productively speculative (Currie, 2021), it’s both synthetic and analytic and depends on the empirical work produced by others. The Pleistocene Social Contract is again paving the way for a much more exciting direction for philosophers interested in human evolutionary riddles. As such, the book is both a must-read for any scholar professionally engaging with the evolution of cooperation and human social evolution, but also a masterful illustration of the value of an empirically-engaged philosophy.

Turning now to the more critical caveats, in the account of how dominance hierarchies were curbed, Sterelny foregrounds the role of hunting as a profitable form of cooperation that makes the detection and policing of cheaters a tractable issue. But if the availability of game is unpredictable and hunting has usually a low success rate – as Sterelny himself recognizes (p. 70) – then strategies for securing backup food sources and allowing efficient foraging become equally or even more important. To gather fallback resources unburdened by toddlers, mothers (or sub-adults) must have substantially relied on forms of reproductive cooperation. Cooperative breeding – group members other than parents (alloparents) helping parents to care for and provision offspring – features as one of the ingredients that supported a much more expanded version of cultural learning (p. 42), but Sterelny seems to assign hunting a special role in getting cooperation off the ground in Homo lineage. Cooperative breeding has an evolutionary history probably as deep as hunting, likely arising with H. erectus and their colonization of novel habitats and consequent adjustments of foraging strategies (Hrdy & Burkart, 2020; van Schaik & Burkart, 2010). There’s reason to suspect a much more interesting story is yet to be told on the role of such factors, together with changes in life-history attributes, and on how they feed into the culture-cooperation co-evolutionary loop.

Second, increasing skepticism on the pervasive egalitarianism of early forager life is becoming visible in the literature (Graeber & Wengrow, 2021; Lewin, 1988; Shennan, 1996; Singh & Glowacki, 2022; Wengrow & Graeber, 2015). Sterelny has already interacted with arguments putting pressure on the relative frequency of pre-agrarian egalitarianism (Sterelny, 2022). However, there’s still room for elaborating on the limits of ethnographic analogy based on recent small-scale foragers as primary pre-Holocene models and on the implications of evidence of considerable social variation among apparently mobile groups (Singh & Glowacki, 2022). This lies at the basis of the standard view defended in The Pleistocene Social Contract. If a focus on such groups represents a still poorly assessed source of bias (for instance, !Kung egalitarianism appears as a historically recent product of interaction with Bantu farmers, who displaced local leaders, and thus does not reflect a general hunter-gatherer lifestyle, Wiessner, 1994), and if more political modes, degrees of mobility and cooperativity were explored than previously appreciated, the overall picture of directionality (at least, for the pre-Holocene period) appears less straightforward than Sterelny describes it. But it makes the final point of how we settled on a permanent system of inequality, while becoming obligate cooperators, no less pressing.

Third, and taking this point on variation into dialogue with band-band interactions, Sterelny’s view distinguishes itself from a Hobbesian universe in which violence was the standing state and intergroup competition and cooperation are causally coupled (Bowles & Gintis, 2011). He’s careful enough not to promote a romanticized, Rousseauian view of the Pleistocene hunter-gatherer lifeways either, but suggests that relations were often civil and direct evidence of violence is limited to late Pleistocene (pp. 115–116). However, a divide seems to persist in the literature on whether antagonistic relations were a significant element of social life prehistory (Kissel & Kim, 2019). There is now non-negligible ethnographic and archaeological evidence of a longer history of intergroup violence among nomadic hunter-gatherer communities than Sterelny allows (Carbonell et al., 2010; Lahr et al., 2016; LeBlanc, 2014; Otterbein, 2011). This indicates that the biases introduced by the preservation lottery might still be a serious concern. But if conflict might have been an affordable option under specific social, material and environmental circumstances (no differently than peace and avoidance was), Sterelny is still right in treating strong selection on groups as a superfluous generalized mechanism to explain earlier cooperative practices (suggesting, however, that the conditions for cultural group selection might have been realized late in the Pleistocene). However, we can imagine the selective profile changing at a more regional scale in contexts with higher population densities, for instance when bands retreated to coastal refugia during Pleistocene climatic cycles with dense and more predictable resources.

Finally, a conclusive note on style. The Pleistocene Social Contract is no doubt a well-argued and clearly written book, with unfussy and clever prose. But it is also information dense. Juggling an array of causal factors to construct a nuanced scenario and not neglecting any relevant piece of evidence is no easy task (hence the frequent use of listing). While this is a treat for practitioners and philosophers of science in practice, newcomers to the field might find at least some parts challenging. But the reward – getting to grips with one of the most comprehensive and brilliant accounts of the evolution of human cooperation, written by one of the most authoritative scholars – is clearly worth the effort.

Acknowledgements

I am grateful to Adrian Currie for useful comments and suggestions on a draft of this review.