Evolutionary Origins of Morality: The element of prosocial concern most likely evolved in the context of shared infant care, which can be found in humans and some New World monkeys

Evolutionary Origins of Morality: Insights From Non-human Primates. Judith M. Burkart, Rahel K. Brügger and Carel P. van Schaik. Front. Sociol., July 9 2018. https://doi.org/10.3389/fsoc.2018.00017

The aim of this contribution is to explore the origins of moral behavior and its underlying moral preferences and intuitions from an evolutionary perspective. Such a perspective encompasses both the ultimate, adaptive function of morality in our own species, as well as the phylogenetic distribution of morality and its key elements across primates. First, with regard to the ultimate function, we argue that human moral preferences are best construed as adaptations to the affordances of the fundamentally interdependent hunter-gatherer lifestyle of our hominin ancestors. Second, with regard to the phylogenetic origin, we show that even though full-blown human morality is unique to humans, several of its key elements are not. Furthermore, a review of evidence from non-human primates regarding prosocial concern, conformity, and the potential presence of universal, biologically anchored and arbitrary cultural norms shows that these elements of morality are not distributed evenly across primate species. This suggests that they have evolved along separate evolutionary trajectories. In particular, the element of prosocial concern most likely evolved in the context of shared infant care, which can be found in humans and some New World monkeys. Strikingly, many if not all of the elements of morality found in non-human primates are only evident in individualistic or dyadic contexts, but not as third-party reactions by truly uninvolved bystanders. We discuss several potential explanations for the unique presence of a systematic third-party perspective in humans, but focus particularly on mentalizing ability and language. Whereas both play an important role in present day, full-blown human morality, it appears unlikely that they played a causal role for the original emergence of morality. Rather, we suggest that the most plausible scenario to date is that human morality emerged because our hominin ancestors, equipped on the one hand with large and powerful brains inherited from their ape-like ancestor, and on the other hand with strong prosocial concern as a result of cooperative breeding, could evolve into an ever more interdependent social niche.

Introduction

Contemplation of law as a natural social phenomenon quickly reveals that it cannot be reduced to purely rational processes and explicit reasoning. It is fundamentally built on (albeit not identical with) our sense for morality, the propensity to differentiate actions, decisions, and intentions between those that are proper and right and those that are improper or wrong (Long and Sedley, 1987). This evaluation can be the result of deliberation, but also of automatic proximate mechanisms such as intuitions that are expressed by a variety of moral emotions, motivations, and preferences which often have a high-urgency feel (Weaver et al., 2014).

Social scientists have traditionally considered morality as a recent, purely cultural innovation, seemingly necessary to keep our otherwise brutish nature under control (e.g., reviewed in Long and Sedley, 1987; de Waal, 2006; Haidt, 2013). In support of this conjecture, what is considered moral in a given culture or society, or what the corresponding systems of laws prescribe, can indeed be quite variable. However, despite this variability in the content of what counts as moral among cultures, there are also elements that seem universal, both with regard to the proximate mechanisms that regulate moral behavior and the content of moral norms. For instance, Barrett et al. (2016) found that across societies, including small-scale societies, humans take an agent's reason for action into account for moral judgments, but they also found independent variation when looking at specific contents, e.g., harm vs. theft, or in how the content influences the role of intentionality. Furthermore, even if conformist transmission could in principle stabilize a variety of behaviors and norms (Chudek and Henrich, 2011), there appears strong canalization in that some kinds of content (such as for instance not to harm others, or engage in parental investment) are more readily considered moral than others (van Schaik, 2016).

Ubiquitous key elements of human morality discussed in this paper are prosocial concern and conformity, as well as the moral contents of doing good, not harming others, and avoiding inequity and incest (van Schaik, 2016). Importantly, these elements are not only expressed when the individual is personally involved, i.e., in individualistic or dyadic contexts, but also in the absence of personal involvement, i.e., in third-party contexts. For instance, moral behavior not only includes the urge to conform to the rules and norms of one's own community, but also evokes strong feelings that others ought to do so as well. The universal presence of these elements of morality across human societies suggests there is an evolved core to morality, which should therefore be amenable to a functional and comparative evolutionary analysis sensu Tinbergen (Tinbergen, 1963; Bateson and Laland, 2013).

Such an evolutionary analysis claims that whenever universal, proximate mechanisms have evolved, they must have done so to fulfill a specific adaptive function. In the first section of this contribution we will argue that the adaptive function of our evolved morality was to enable the highly interdependent life-style of Pleistocene hunter-gathers.

An evolutionary analysis of human morality also includes the examination of its phylogenetic origin, to which we will turn in the second section. Whereas full-blown human morality, which includes explicit moral reasoning and evaluation, may well be unique to humans, some of its elements or building blocks are not, and we can use data from non-human primates to trace the evolutionary history of each of them separately. An obvious first, and very popular, step is to look at the great apes, and in particular the chimpanzees and bonobos (e.g., de Waal, 2006), to investigate the possible presence of a specific building block in our closest relatives. However, a broader and more informative comparative approach consists in mapping the presence or absence of each of these building blocks or traits in a broader set of species, to then test which factor best predicts this pattern of distribution (MacLean, 2016). If the specific case of humans fits such an identified pattern, this allows us to identify the evolutionary context of the emergence of this trait. This approach thus ideally allows not only to identify that a trait is or is not unique to humans, but also why it is present in a given set of species, including humans.