Ancestral social environments plus nonlinear benefits can explain cooperation in human societies

Abstract

Human cooperation (paying a cost to benefit others) is puzzling from a Darwinian perspective, particularly in groups with strangers who cannot repay nor are family members. The beneficial effects of cooperation typically increase nonlinearly with the number of cooperators, e.g., increasing returns when cooperation is low and diminishing returns when cooperation is high. Such nonlinearity can allow cooperation between strangers to persist evolutionarily if a large enough proportion of the population are already cooperators. However, if a lone cooperator faces a conflict between the group’s and its own interests (a social dilemma), that raises the question of how cooperation arose in the first place. We use a mathematically tractable evolutionary model to formalise a chronological narrative that has previously only been investigated verbally: given that ancient humans interacted mostly with family members (genetic homophily), cooperation evolved first by kin selection, and then persisted in situations with nonlinear benefits as homophily declined or even if interactions with strangers became the norm. The model also predicts the coexistence of cooperators and defectors observed in the human population (polymorphism), and may explain why cooperators in behavioural experiments prefer to condition their contribution on the contributions of others (conditional cooperation in public goods games).

On the origin of the extinction of the (human) species

“…Interactions among human beings are pointed out as an adaptive advantage for our species, that seems also to be invariant across time and space, surpassing temporally and geographically the human history (Apicella & Silk, 2019;Boik, 2020;Gilbert, 2021;Hilbe et al, 2018;Kristensen et al, 2022;Murase et al, 2022;Roberts & Stewart, 2018). Like other species, humans cooperate and compete in a wide range of situations (Burkart et al, 2014;Gilbert, 2021;Hamilton, 1964;Ribeiro da Silva et al, 2015;Trivers, 1971).…”

“…It is likely that the combination of humans' basic instincts to thrive with their unique and increasing cognitive abilities (e.g., symbolism, complex communication, technological sophistication) and physical characteristics have been crucial for our species to persist and to colonize world's continents (e.g., Gilbert, 2021;Raven, 2022;Roberts & Stewart, 2018). These instincts to thrive (e.g., conquer new territories, gain power over animal and plant species) are well evident across human history, both at a local (e.g., hunter-gatherers; Gilbert, 2021;Kristensen et al, 2022) and at a global level (e.g., Age of Discovery or Age of Exploration; Paine, 2020), and are still very present, exceeding also the limits of planet Earth (e.g., space expeditions; see Le Roy et al, 2023 for an overview on this topic). Although these instincts are not harmful per se, they usually entail a series of humans' actions that negatively affect all Earth ecosystems, even those not directly in contact with humans (e.g., deep sea; Bergmann, et al, 2022;Pinto et al, 2023).…”

“…Like other species, humans cooperate and compete in a wide range of situations (Burkart et al, 2014;Gilbert, 2021;Hamilton, 1964;Ribeiro da Silva et al, 2015;Trivers, 1971). The origin of human cooperation is still an evolutionary puzzle from a 'selfish' Darwinian perspective, as it often involves a conflict between other's interests and individual's interests (Darwin, 1859;Kristensen et al, 2022). Hamilton's kin selection theory provides a congruent explanation for cooperation between relatives as one is still passing on its genes to the next generation (Hamilton, 1964).…”

“…The development of agriculture and the domestication of animals (around 11 000 years ago) allowed our ancestors to remain together for long periods in a single place, increasing and expanding their interactions from relatives to non-relatives (Burkart et al, 2014;Griffin et al, 2004;Kristensen et al, 2022;Raven, 2022). In an extended version of Hamilton's kin selection theory, this new lifestyle impacted on the selection for cooperation, as it became dependent upon the scale of competition (relatively local to relatively global), i.e., although limited dispersal usually leads to a higher relatedness, it can also lead to more local competition between relatives and non-relatives (Apicella & Silk, 2019;Hamilton, 1964;Griffin et al, 2004).…”

“…In an extended version of Hamilton's kin selection theory, this new lifestyle impacted on the selection for cooperation, as it became dependent upon the scale of competition (relatively local to relatively global), i.e., although limited dispersal usually leads to a higher relatedness, it can also lead to more local competition between relatives and non-relatives (Apicella & Silk, 2019;Hamilton, 1964;Griffin et al, 2004). Moreover, it is important to highlight that cooperation seems adaptive only if a substantially proportion of the population are already cooperators, otherwise cooperators would not have an adaptive advantage (Kristensen et al, 2022). In this regard, some authors argue that competition is the primary driving force in evolutionary change, and humans are not an exception (Abreu et al, 2019;Celiker & Gore, 2012;Dawkins, 1976Dawkins, /2006Govaert et al, 2018;Griffins et al, 2004;Hogle et al, 2023;Monaco et al, 2022;Nair et al, 2019;Trivers, 1971;Wang et al, 2020;Yamamichi et al, 2022).…”