Stibbard-Hawkes and von Rueden call for further cross-cultural and quantitative research to disentangle the socio-ecological correlates of egalitarian processes. They point out that these processes’ “relative importance to the distribution of material resources and political power is presently under-researched.” The studies they cite focus on the direct function of these processes in egalitarian societies. To complement their approach and close an important gap in their argument, I strongly suggest including the study of mechanisms creating and maintaining inequality and unfreedom: exploitation and slavery in particular.

First, a paradigm shift from outcomes to processes is conceptually compatible with contemporary slavery studies. The static, outcome-orientated definition restricts further understanding of actual human behaviour, as Stibbard-Hawkes and von Rueden address. Defining slavery as the ownership of humans and considering it as the extreme opposite of individual freedom only applies to a few societies that have clear definitions of ownership and individual freedom, such as the Atlantic or Graeco-Roman worlds. Thus, historians and anthropologists have proposed that the extreme negation of individual autonomy and status – that is, slavery – should also be understood from a process perspective (Kopytoff, Reference Kopytoff1982; Pargas, Reference Pargas, Pargas and Schiel2023; Winnebeck et al., Reference Winnebeck, Sutter, Hermann, Antweiler and Conermann2023). This processual perspective places different forms of slavery on a spectrum of unfree and dependent conditions (Pargas, Reference Pargas, Pargas and Schiel2023). People living in societies are involved in varying degrees of asymmetrical dependency and protection; those outside this protection are prone to enslavement (Acemoglu & Robinson, Reference Acemoglu and Robinson2019; Snyder, Reference Snyder2010). Therefore, it is conceptually valid to compare egalitarian societies which guarantee individual autonomy with institutions that severely restrict the autonomy of some members.

At the same time, many models and theories view slavery and inequality as consequences of self-interested motives. The processes proposed by Stibbard-Hawkes and von Rueden are also motivated by self-interested individual concerns rather than equality. Thus, understandings of how socio-ecological factors favour egalitarianism or slavery can be achieved using the same self-interested individual paradigm: Why do self-interested individuals sometimes end up in egalitarian situations, while in other situations, they end up in slavery? Expanding the scope of the analysis to include more types of societies enables further cross-cultural and quantitative research.

Therefore, slavery can be considered an important “control group” in the analysis of egalitarianism, providing examples of what can happen when certain processes or socio-ecological factors are absent. Slavery in subsistence groups and non-agricultural societies was not unusual (Cameron, Reference Cameron2011; Donald, Reference Donald1997). Cameron (Reference Cameron and Billman2025) proposes that, in these small-scale societies, slaves served as instruments for their masters to avoid social levelling mechanisms, as their lack of kinship made them easier to control. Applying the framework of Stibbard-Hawkes and von Rueden, we also gain valuable insights into the relationship between status-levelling and leadership inequality. Therefore, analysing the socio-ecological conditions that favour slavery also answers the question of what deters the status-levelling process.

Furthermore, the inclusion of slavery allows for comparative institutional analysis. In addition to ideal natural experimental scenarios, which provide strong causal evidence, comparing neighbouring societies with different degrees of personal autonomy also offers new insights. For instance, Wengrow and Graeber (Reference Wengrow and Graeber2018) sought to explain why neighbouring groups in the southern Northwest Coast and northern California made distinct institutional choices regarding individual autonomy – some with slaves and some without. They highlighted another critical socio-ecological condition: the interaction between societies. The choices made by your neighbours influence your own choices; the strategic interactions also shape institutional choices. Wengrow and Graeber (Reference Wengrow and Graeber2018) proposed that exploitative neighbours actually reinforced the values of “autonomy and personal piety” in non-slave-taking societies.

Moreover, expanding the scope of the analysis also increases the potential for quantitative research. This applies to both theoretical and empirical studies. Numerous quantitative models on the origins of slavery and serfdom have been built by economists and economic historians (e.g., Acemoglu & Wolitzky, Reference Acemoglu and Wolitzky2011; Domar, Reference Domar1970; Lagerlöf, Reference Lagerlöf2009). Most are based on the assumption of maximising self-interest. The target article’s framework enables us to incorporate the insights of these models into our understanding of egalitarianism. For example, Lagerlöf (Reference Lagerlöf2009) modelled the influence of two critical socio-ecological factors, land productivity and population density, on the choice of institutions: egalitarianism, slavery, or free labour. Although anthropologists may disagree with some of the models’ narrow assumptions, these mathematical models rigorously guarantee the logical consistency of arguments – Rusch et al. (Reference Rusch, Schmitt, Teufel, Vater, Luetge and Thejls Ziegler2026) provide an overview and discussion of the respective models available in the literature.

Finally, the quantitative empirical literature on inequality and slavery meets the demand for cross-cultural research into the socio-ecological correlates of egalitarian processes. Modern digitalised anthropological records, e.g., Jorgensen, Reference Jorgensen1980, or D-Place (https://d-place.org/), provide further data for analyses, enabling researchers to examine hypotheses quantitatively (Lowes, Reference Lowes, Bisin and Federico2021). Some economists have attempted to find causal evidence using limited historical data and modern econometrics techniques to explain the origins of hierarchical institutions, such as the state (Mayshar, Moav, & Pascali, Reference Mayshar, Moav and Pascali2022) and serfdom (Matranga & Natkhov, Reference Matranga and Natkhov2025). However, most empirical studies only provide strong correlational evidence on the determinants of inequality and slavery (Fenske, Reference Fenske2013; Haynie et al., Reference Haynie, Kavanagh, Jordan, Ember, Gray, Greenhill and Gavin2021; Hrnčíř & Květina, Reference Hrnčíř and Květina2017; Smith & Codding, Reference Smith and Codding2021). Including societies with varying degrees of individual autonomy in statistical analyses will reveal more insightful socio-ecological patterns.

In summary, slavery provides a useful perspective through which to understand egalitarianism. The approach taken in the target article enables us to link two branches of literature, providing a broader view of individual autonomy. Ignoring the coercive institutions that existed alongside egalitarian societies would distort our understanding. Therefore, future research on egalitarianism should incorporate human unfreedom and exploitation. Studying processes and conditions that enhance inequality and dependency not only helps us to understand egalitarianism but can also provide novel insights into contemporary inequalities.