A niche of their own: population dynamics, niche diversification, and biopolitics in the recent biocultural evolution of hunter-gatherers

Journal of Anthropological Archaeology 57 (2020) 101120

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A niche of their own: population dynamics, niche diversification, and biopolitics in the recent biocultural evolution of hunter-gatherers Aaron Jonas Stutz

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Department of Anthropology, Emory University, 207 Anthropology Building, 1557 Dickey Drive, Atlanta, GA 30322, USA Bohusläns Museum, Box 403, 451 19 Uddevalla, Sweden

A R T I C LE I N FO

A B S T R A C T

Keywords: Biocultural evolution Niche construction Energy extraction Population elasticity Population regulation Hunter-gatherers Cross-cultural analysis Socio-political complexity Biopolitics Niche diversification

Three decades have passed since Keeley published his comprehensive exploration of cross-cultural variation in hunter-gatherer social complexity, sedentism, and storage across diverse environmental and demographic conditions (Keeley, L.H., 1988. Hunter-gatherer economic complexity and “population pressure”: A cross-cultural analysis. J. Anthropol. Archaeol. 7, 373–411. https://doi.org/10.1016/0278-4165(88)90003-7). This article reconsiders Keeley’s work, shifting theoretical focus to niche construction, biocultural adaptation, and the biopolitics of inclusion and exclusion. In recent millennia, human niche construction has become defined by intense matter and energy extraction at or across key hydrospheric, atmospheric, and lithospheric regime boundaries. Associated global population growth has depended on the biocultural evolution of positive elasticity in energy extraction rates, with respect to labor inputs. This article presents a statistical reanalysis of Keeley’s cross-cultural data, documenting the niche-divergence between immediate-returns hunter-gatherers and delayed-returns, storage-dependent foragers. It is argued that the intricate relationships among niche elasticity, population-growth elasticity, niche diversification, and the biopolitics of inclusion and exclusion have dynamically shaped ecological enrichment—in the form of patch engineering—and demographic disruption—mainly in the form of dispersal, migration, raiding, and warfare. This article aims to offer new perspectives on the systemic coupling among political complexity, economic development, inequality, and environmental impacts in post-Pleistocene human systems.

1. Introduction The 1980s was a pivotal decade in hunter-gatherer research. New theoretical concepts about the practical management of social relationships, resources, and land in egalitarian systems were developed or refined. The ethnography of “immediate returns” hunter-gatherers would become subject to intense critique (Wilmsen and Denbow, 1990). However, fieldwork across multiple continents and major islands set the stage for more deeply explaining the emotional, embodied, relational and material aspects of collective action, production, exchange, and family formation in landscape and cultural context (Ingold et al., 1988a, 1988b). At the same time, scrutiny of archaeological and ethnographic source information established that socio-politically complex “delayed-returns” hunter-gatherers must be studied to understand the prehistoric origins of storage, sedentary settlement, and institutionalized inequality (Bender, 1978; Hayden, 1981, 1981; Ingold, 1983; Kelly, 1983; Price and Brown, 1985; Testart, 1982; Woodburn, 1988, 1980). Focusing on Keeley’s cross-cultural dataset, first presented

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in this journal three decades ago (1988), this article presents a re-examination of key theoretical notions and empirical observations from that period, considered in light of more recent models and concepts from a trio of disparate—and perhaps unlikely—sources: economic demography, niche construction theory, and biopolitical theory. The rich cultural and ecological data analyzed, discussed, and refined in the 1980s (Hayden, 1981; Keeley, 1988; Kelly, 1983; Testart, 1982) may be constructively integrated with Woodburn’s (1980, 1982, 1988) dichotomous framework for characterizing culturally embedded foraging economies, which were argued to separate into immediatereturns (IR) and delayed-returns (DR) alternatives. Similar to societies with delayed-returns agricultural technologies, food-processing-intensive and storage-dependent DR hunter-gatherer systems are most often situated in relatively large, densely settled social networks, exhibiting hierarchical structure across population and temporal dimensions, from daily to intergenerational time-frames (Fig. 1) (Binford, 2001; Hamilton et al., 2009, 2007b, 2007a; Johnson, 2014; Price and Brown, 1985). In contrast, IR hunter-gatherer systems—which have

Address: Department of Anthropology, Emory University, 207 Anthropology Building, 1557 Dickey Drive, Atlanta, GA 30322, USA. E-mail address: [email protected].

https://doi.org/10.1016/j.jaa.2019.101120 Received 10 October 2018; Received in revised form 8 October 2019 0278-4165/ © 2019 Elsevier Inc. All rights reserved.

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Fig. 1. Population structure in delayed-returns (DR) foraging societies across evolutionarily relevant temporal scales, illustrating that DR economies tend to be embedded in a hierarchical population structure organized by technologies of durable aggregation and co-residence. Values for population-scale nuclear family and coresidence units are based on Hamilton et al. (2007b).

Fig. 2. Population structure in immediate-returns (IR) foraging societies across evolutionarily relevant temporal scales, illustrating that family formation and family cycles strongly influence the social relationships and networks mediating fission-fusion co-residence practices, under higher residential mobility levels. Values for population-scale nuclear family and co-residence units are based on Hamilton et al. (2007b).

and Bar-Yosef, 2010). In this article, I utilize Keeley’s (1988, 1995) relatively detailed measures of secondary above-ground biomass production, sedentism, and storage, as I investigate the conditions under which human societies have succeeded in extracting higher and higher levels of matter and energy from our surroundings—that is, in achieving positive elasticity of extraction, which has been a necessary condition for long-term human population growth (Stutz, 2014a). I explore how the post-Pleistocene emergence of DR hunter-gatherers—not only that of DR agricultural societies—contributed to the complex systemic interplay among human niche construction, biocultural adaptation and globally transformative demographic dynamics. In statistically reconsidering Keeley’s original work, this study also

been documented archaeologically and ethnographically from the tropics to sub-arctic latitudes—exhibit a substantial range of omnivorous foraging economies, usually involving frequent residential-camp moves and flexible fission-fusion co-residence patterns (Fig. 2) (Binford, 1980; Grove et al., 2012; Kelly, 2013; Woodburn, 1982; Yellen, 1977). IR hunter-gatherer technologies and socio-cultural systems of family formation, reciprocity, alliance-building, and social levelling evolved with life-history/embodied capital adaptations in the Pleistocene (Hill et al., 2009, 2014; Hill and Hurtado, 1996; Kaplan et al., 2010, 2009). However, DR foraging societies have much more recent prehistoric origins. At the earliest, in the Levant, limited Natufian hunter-gatherer storage practices were adopted at the very end of the Pleistocene (Price 2

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organized violence, care, aging and dying, rights to land or land tenure, social participation and migration.

involves extended theoretical background and discussion sections, yielding the following tripartite outline. First, the background is presented in the following sections, “From Population Pressure to Niche Diversification” and “Hunter-Gatherers and the Elasticity of Human Population Growth.” These parts lay out my theoretical motivation for reanalyzing Keeley’s hunter-gatherer cross-cultural data. I argue for shifting away from Keeley’s original explanatory focus on population pressure, considering instead niche construction’s interrelationship with demographic dynamics. Human biocultural evolution in the Holocene has involved intricate feedbacks among niche diversification, population regulation regimes, and the emergence of positive population elasticity—that is, the systemic capacity to convert marginal rise in energy captured into demographic growth. It is here that reanalysis of Keeley’s dataset becomes plainly relevant. His high-quality cross-cultural samples of IR and DR hunter-gatherer societies—with their constituent populations and foraging territories—support testing whether IR and DR foraging regimes comprise different niches, in terms of energy flow and biomass. Moreover, the Keeley dataset also supports testing whether—in ethnographic and ethnohistoric cross-cultural perspective—delayed-returns foraging has been sufficient to achieve positive elasticity of population growth with respect to labor inputs. Second, the “Methods” and “Results, Parts I and II” sections present how Keeley’s data, when analyzed with nonparametric statistical methods more suitable to the samples and observations, provide a very strong confirmation—but also some critical clarifications—of his originally inferred relationship between secondary above-ground biomass production and hunter-gatherer population density. As detailed below, the results support falsifying Keeley’s specific claim that population pressure has generally been the efficient cause of sedentism. At the same time, the new statistical analyses paint a more nuanced picture of the ties among institutionalized inequality, feasting rituals, storage, and higher population-density demographic regimes, raising important theoretical questions about the complex dynamics involving niche construction, niche diversification, and biocultural adaptation. Third, the discussion and conclusion offer a conceptual pathway for taking on these theoretical challenges. IR and DR hunter-gatherer biocultural systems—respectively, fundamentally defined by the absence versus presence of food storage, at least to cover poor-season caloric shortfalls—occupy thoroughly distinct energy-extraction and biomass regimes. In short, they are fit to different biocultural niches. Yet, storage itself cannot plausibly be a primary driver of IR-DR niche diversification in the Holocene. As confirmed in the reanalysis presented here, the social coordination involved in managing food resource acquisition, processing, storage, distribution and consumption is generally different than for immediate-returns foraging. DR social networks are much more often organized hierarchically, mediated by distinctive patterns of symbolic and material negotiation over the nutritional and political stakes at each step in the labor-distribution-consumption cycle (cf. Keeley, 1988, 1995). It is argued that the concept of biopolitics—developed in the embodied political theoretical frameworks detailed by Foucault (1990) and Agamben (1998, 2016)—is highly relevant for understanding why storage-mediated foraging nicheconstruction occurred in the Holocene. DR foraging is cross-culturally, statistically associated with institutionalized political and economic inequality and socially integrating rituals. I argue that the emergence of DR hunter-gatherer biocultural systems must be understood, not only in terms of demography, storage technologies, labor mobilization and institutionalized inequality (Arnold et al., 2015), but also in terms of their intersection, in the realm of biopolitics. It is through biopolitical judgments and acts of inclusion and exclusion—unfolding through and across bodies at multiple social, energy-flow and geographic scales—that sedentary settlement and storage practices would have been negotiated and adopted, shaping the novel high-energy-extraction-rate DR forager niche in the Holocene. I suggest that biopolitics is a multiscalar socio-geographical phenomenon, encompassing not only labor and consumption, but also family formation, childhood, coming of age,

2. From population pressure to niche diversification Building on and durably influencing cross-cultural analyses of foragers’ societies, their demographic conditions, and their environments, Keeley convincingly confirmed that hunter-gatherer population densities are significantly affected—and apparently constrained—by available, consumable biomass production (Binford, 2001; Tallavaara et al., 2018). However, Keeley took a critical step further. He drew a key conclusion, that human population pressure on ecological resources was the “efficient cause” of sedentism, storage, and sociopolitical complexity (Keeley, 1988). Reaching this conclusion required a premise that was not necessarily logically or empirically warranted. Keeley assumed that the ratio of human population to edible above-ground biomass production measured population pressure itself. He did acknowledge that most complex hunter-gatherer societies—persisting at higher population densities relative to terrestrial biomass production—rarely faced subsistence shortfalls. In comparison, mobile egalitarian foragers in harsher, more continental environments regularly experienced starvation episodes (Keeley, 1988). Cautiously stated, this observation did not necessarily strengthen his more general conclusion—that is, that population pressure is the efficient cause of sedentism, storage, and socio-political complexity. Keeley acknowledged that his data on starvation risks, in particular, suggest something else. Mobile, low-density (IR) hunter-gatherers in less productive continental environments often dealt with more acute population pressure on resources. It does not inevitably follow that these IR groups would eventually adopt sedentism and storage, transitioning into DR foraging societies to buffer the demographic stress (Puleston and Winterhalder, 2019). Keeley did cogently argue that, in the face of normal climatic fluctuations, DR societies would have faced only marginally reduced foraging returns during bad years. In contrast, IR societies would more often have suffered serious Malthusian checks under similar weatherforced downturns in biomass productivity and work efficiency (see Keeley, 1988, Fig. 6). He noted that recurrent exposure to chaotic fluctuations in marginal foraging returns could explain how “complex” delayed-returns societies—with institutionalized sociopolitical inequality—might have thrived bioculturally, having been guided to adopt a series of buffering innovations. However, he did not offer a sufficient explanation for how and why an IR system could initially escape a population-ecosystem relationship involving strong Malthusian constraints, taking sufficient risks (Fitzhugh, 2001)—or mobilizing necessary levels of collective action—to adopt the most basic DR organizational and technological innovations, minimally involving food storage for daily energy budgets during critical seasonal periods, thus more effectively insuring against seasonal and inter-annual environmental fluctuations (Puleston and Winterhalder, 2019; Winterhalder et al., 2015; Winterhalder and Goland, 1997). This is a key reason to reconsider Keeley’s core, operational assumption, that the relationship between prevailing above-ground biomass production and human demographic density directly reflects population pressure. As Keeley documented—and as confirmed statistically below—DR hunter-gatherer societies have tended to rely on sedentary settlement, which situated their food-storage technologies in a durable, socially-structuring built environment. The apparent crosscultural associations among sedentism, storage, and higher population density might not necessarily reflect relatively greater ecological pressure. They might simply reveal a potentially resilient delayed-returns biocultural adaptation to a gradually constructed, high-extraction-rate niche.

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3. Hunter-gatherers and the elasticity of human population growth

systemic pitfalls to achieving a persistently successful mix of investment in technology, social organization, fertility, and intergenerational transfers (Lee et al., 2009; Lee and Tuljapurkar, 2008; Lee, 1986; Puleston and Tuljapurkar, 2008). Under a wide range of conditions—and notably, not at all restricted to IR foraging systems—Malthusian regulation can rapidly dampen and tightly constrain demographic returns on investment, inhibiting innovation and growth in local or unstructured natural fertility populations (Puleston et al., 2014; Puleston and Winterhalder, 2019). Moreover, political centralization—in imposing tribute demands, compelling corvée labor, or mobilizing communal-storage investment—can constrain family-level investment, leading to risk-averse behavior, even as the hegemonic political institutions and practices limit the overall population, seemingly paradoxically reducing susceptibility to a range of Malthusian shocks (Winterhalder et al., 2015). Thus, formal approaches have refined Malthusian and Boserupian ideas (Cohen, 1995a; Kremer, 1993; Lee, 1986; Puleston and Winterhalder, 2019; Wood, 1998), even considering Marx’s critique of Malthus (Stutz, 2014a). This work has now provided a more substantial set of models for how demographic rates may relate to technological and organizational innovation within and among socio-politically bounded, ideologically constituted groups—considered at a local scale (Lee et al., 2009; Lee and Tuljapurkar, 2008; Puleston and Tuljapurkar, 2008; Puleston et al., 2014; Winterhalder et al., 2015) or, alternatively, in a simplified “cartoon-version” of a globalizing political-economic system (Cohen, 1995b; Stutz, 2014a). These models rigorously build on and refine earlier discussions of cultural change in dynamical ecological systems (e.g., Flannery, 1973), supporting the theoretical position that, contra Keeley, population pressure itself is implausible as a prime mover for major socio-technological and demographic transitions (Puleston and Winterhalder, 2019; Richerson et al., 2001; Stutz, 2009; Wood, 1998). I argue that, instead, we have to consider complex feedbacks among diversifying patch engineering, ideological and institutional niche construction, technological change, intergroup interaction, and local investment in fertility and intergenerational transfers, especially in the face of climatic variability. It suffices to underscore that human evolutionary uniqueness involves the potential for long-term positive elasticity in population growth, and researchers are only beginning to explore this phenomenon in terms of formal models in economic demography and niche construction.

At first glance, foraging populations would seem to offer little insight into modern, global population growth, the positive elasticity of which supported super-exponential increase across much of the 19th and 20th Centuries (Stutz, 2014a). The economic concept of elasticity simply refers to how y responds functionally to change in x. Thus, y would exhibit positive elasticity if it grew disproportionately as x increased marginally. An inelastic response to rising x would involve constant or diminishing growth in y. Although relatively rarely discussed in anthropology, elasticity has figured centrally in a recent, elegant study (Jones and Tuljapurkar, 2015), which modeled and analyzed age-specific fertility trade-offs in human and non-human primate life-history strategies. Jones and Tuljapurkar (2015) show that, across a relatively extended adult reproductive period, humans exhibit substantial positive elasticity of fertility, despite also having relatively high basal metabolic rates (Barrickman et al., 2008; Isler and van Schaik, 2012, 2009; Pontzer et al., 2016) and intense “downward” intergenerational transfer flows (Kaplan and Robson, 2002; Lee, 2008, 2003; Stutz, 2009). In particular, persistent positive elasticity of fertility in the human female life-history adaptation can buffer against spikes in metabolic stress, offspring-care costs, or even juvenile mortality. This allows our species to maintain demographic resilience in more unpredictable environments, while often raising total fertility rates, when compared with our great ape relatives. The potential for positive elasticity in demographic growth, then, appears systemically connected to the persistent prime-adult potential for positive elasticity in fertility, having evolved in a niche often constituted by high variability and unpredictability of energy balance and energy flux (Ellison, 2001; Gurven et al., 2016; Winterhalder and Leslie, 2002). More recently, in the last few centuries, globalization processes have involved international capital transfers, more open international trade, global communications media, but also complex local processes of resilience, resistance, and identity formation (Kentor, 2005, 2001; Knauft, 2002). This multiscalar “globalization complex” surely has much to do with the human population’s long-term positive elasticity with respect to resource inputs (Cohen, 1995a; Stutz, 2014a). Still, positive population elasticity is nothing new for humans. Range expansions have shaped human population biology since the Lower Pleistocene (Gamble, 2003; Templeton, 2002; Wells and Stock, 2007). Genomic and archaeological evidence trace regional trends of sustained, millennial scale population growth—among foraging and farming societies alike—since the early or mid-Holocene (Veeramah et al., 2018; Zahid et al., 2016). The study of population growth elasticity would benefit from greater interdisciplinary attention, including a comparative perspective that would consider variation in the conditions and causes of demographic change at different temporal, spatial, and population scales, from Pleistocene hunter-gatherers to contemporary globalizing communities.

3.2. Population elasticity in human prehistory Positive growth elasticity can hardly be an intrinsic aspect of human adaptation. This point is analogous to critiques of the classic populationpressure argument, in which a high intrinsic rate of increase is taken to be a fundamental factor—essentially exogenous to cultural decisionmaking systems—favoring the adoption of economic innovations when marginal returns to labor and investment fall (Boserup, 1965). From an evolutionary perspective, constraints on survival and fertility—including predation, parasite load, nutrient and energy availability, lifehistory and resource-transfer strategy trade-offs, intraspecific conflicts of interest and competition, and interspecific competition—are key selective pressures on biological populations. Hominin evolution must be considered in light of these long-term constraints on population growth. Range expansions allowed total human census size to rise over the Pleistocene, but sustained cycles of innovation-driven growth may have only rarely supported rise in local population densities (Boone, 2002; Powell et al., 2009). Ecological modeling of European Middle and Upper Paleolithic densities, based on known archaeological site distributions, has yielded remarkably low census estimates, mainly driven by apparent socio-technological constraints on intensely colonizing—and not just occasionally exploiting—more heavily forested or higher-elevation zones (Banks et al., 2013, 2008; Bocquet-Appel et al.,

3.1. Formal models of human energy-extraction and population elasticity Formal models illustrate how systemic changes in innovation rates or the scalability of production systems can generate growing resourceextraction rates, which can sustain—in turn—positive elasticity of population growth (Cohen, 1995a, 1995b; Richerson et al., 2001; Stutz, 2014a). These theoretical possibilities—involving innovation-driven “Boserupian expansion” (Lee, 1986; Wood, 1998); density-dependent innovation thresholds (Richerson et al., 2001); or long-term feedbacks between economies of scale and population growth (Cohen, 1995b; Powell et al., 2009; Stutz, 2014a)—are important to scrutinize. Although there are logically plausible paths to recurrent cycles of innovation and population growth, it is not entirely clear how and why intergenerational-scale positive feedbacks have been initiated and sustained in real-world conditions. Indeed, theoretical models also reveal 4

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and early historic ranges for which have been extrapolated from fragmentary records, utilizing very simple models of population densities and inhabited areas (Cohen, 1995a; Klein Goldewijk et al., 2010)—suggest sustained population elasticity from the PleistoceneHolocene transition to (very) roughly 2000 BP. The most parsimonious hypothesis that may be derived from the more recent global estimates is that positive population elasticity became even stronger over the past several hundred years. Only recently, from the late 20th Century (ca. 1980–1990 CE) onward, has it exhibited a significant reduction, as the global demographic rate of increase has begun to decelerate (Stutz, 2014a). Change in population growth elasticity is certainly an intriguing biocultural evolutionary phenomenon. Critically, post-Pleistocene positive population elasticity has involved not only economies of scale and productivity-raising innovations; it has also involved a tightly interrelated rise in matter and energy extraction (Stutz, 2014a). The demographic processes shaping post-Pleistocene human population growth have involved non-linear coupling to growth in aggregate material and energy consumption (Burger et al., 2012, 2011; DeLong and Burger, 2015; Wrigley, 2013). During the Holocene epoch (< 11,700 BP), these energy and matter flows have been conspicuously facilitated through extractive technologies. Humans have recurrently altered the biosphere—initially, in regional food webs, and later, globally across its interfaces with atmospheric, hydrospheric, and lithospheric regimes (Asouti et al., 2015; Asouti and Kabukcu, 2014; Boivin et al., 2016; Braje and Erlandson, 2013; Lewis and Maslin, 2015; Stephens et al., 2019; Waters et al., 2016; Yeakel et al., 2014). An important implication is that, when human population increase has involved positive elasticity, so has niche construction yielded positive elasticity of energy extraction rates—that is, population carrying capacity has increased through biocultural evolutionary processes. Under such conditions, changes in innovationadoption and economies of scale have disproportionately affected the foodwebs of which human populations are part, along with habitats that shape and are shaped by those foodwebs (Boivin et al., 2016; Stephens et al., 2019).

2005; Bocquet-Appel and Degioanni, 2013). Thinly distributed, more tenuously networked Middle Paleolithic populations may have faced significantly greater challenges to developing predictable seasonal mobility patterns, in order to exploit rich, but spatially patchy, timesensitive plant and animal resources (Henry et al., 2017; Stiner and Kuhn, 1992). Whatever the rise in population density that occurred in the Eurasian later Middle Paleolithic and early Upper Paleolithic (ca. 45–30 kya) (Mellars and French, 2011; Morin, 2008; Speth and Clark, 2006; Stiner and Kuhn, 1992), it appears that European Gravettian metapopulations eventually succumbed to substantial demographic contraction, as the Last Glacial Maximum reduced habitable land surface, average temperatures, precipitation, and primary biomass production across the continent (ca. 30–20 kya) (Tallavaara et al., 2015). Local or regional population declines are now also well-documented for later time periods. Comprehensive reviews and analyses of radiocarbon dates show that, at least occasionally, regional hunter-gatherer populations went extinct during the Holocene. These episodes appear to have been forced—following a noticeable multi-generational lag—by periods of climate-caused environmental stress (Kelly et al., 2013). Regional agricultural and herding economies in prehistoric Britain were also impacted by Holocene climatic fluctuations, with cooler periods driving episodes of demographic contraction (Bevan et al., 2017; Downey et al., 2016; Shennan et al., 2013). Positively elastic population growth is likely something that may emerge in certain biocultural evolutionary contexts, but ecologically, it is expected to be transient. In this light, the modern super-exponential population growth of the previous few centuries began to decelerate in recent decades, with substantial implications for our extant, globalized biocultural system’s resilience (Fig. 3) (Cohen, 1995a; Kremer, 1993; Stutz, 2014a; United Nations, 2017). 3.3. From post-pleistocene biocultural evolution to “Anthropocene-Like” population dynamics While positive population elasticity would not have been a constant in human evolution, this phenomenon appears to have dominated our global demographic history since the end of the Pleistocene, ca. 12,000 BP. As Fig. 3 illustrates, world population estimates—the prehistoric

Fig. 3. Log-log plot of change in global human census size, from 12,000 years ago (YA, measured before 2016) to the present (see Supplementary Information: S1A Table). 5

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Fig. 4. Distribution of western North American delayed-returns foragers in Keeley’s cross-cultural sample. The western North American societies include 48 out of the 50 DR foraging groups that Keeley studied. Only the Siberian Nivkh (Gilyak) and Greenland Angmaksalik foragers occupied territories outside this super-region. Base map credit: Google Earth.

2012), DR foragers emerged alongside the farming and herding systems that were part of post-Pleistocene diversification in biocultural adaptation, political evolution and niche construction (cf. Arnold et al., 2015). A new analysis of Keeley’s (1988, 1995) dataset of 96 huntergatherer societies allows us to test the following hypotheses: that DR foragers constructed a distinct niche, and that DR forager systems can achieve the kind of elasticity in energy extraction necessary for population growth seen so clearly in more recent, globalizing agriculturebased systems (Cohen, 1995a; Stutz, 2014a).

3.4. Hunter-gatherers and population elasticity It is here that a consideration of human foragers—and of Keeley’s (1988) cross-cultural dataset—comes into focus. I underscore that, in order to understand both human population-growth elasticity and niche construction, we still need to clarify how fertility, mortality, and migration are dynamically—and critically, biopolitically—coupled to the socio-technological systems that facilitate resource extraction from the wider ecosystem. (The term biopolitics has been introduced above. I explain and consider the concept in depth in the “Discussion” section below.) We must also investigate how human population densities and technological systems impact those supporting ecosystems. On the one hand, human evolution has fundamentally involved a long-term dynamic between adaptation and niche construction in immediate-returns foraging populations, across the Pleistocene epoch (ca. 2.5 mya – 12 kya). The biocultural evolution of IR forager adaptations and niches established the subsequent Holocene conditions in which super-exponential population growth and “anthropocene-like” global ecological alterations unfolded. On the other hand, even as IR foraging adaptations remained resilient well into the 20th Century (Kelly, 2013; Stutz,

4. Methodological considerations for re-analyzing Keeley’s crosscultural dataset The cross-cultural cases analyzed in this article come from Keeley’s hunter-gatherer sample (n = 96). The dataset was published in initial form in 1988 and presented in revised form in 1991 and, finally, in 1995. The latter version is used here. Keeley very cautiously screened out ethnographic cases in which foraging societies used high-efficiency hunting technologies (firearms and horseback) or engaged in substantial agricultural production or cash labor (Murdock, 1967). 6

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Although Kelly’s (Kelly, 2013, 1983) sample is similarly filtered and carefully validated through repeated source-checks, Keeley’s slightly more restrictive set has a series of attributes helpful for inquiry into the relationships among population density, niche construction, and resource extraction rates. Notably, Keeley recorded food storage practices following the storage variable codes in the Ethnographic Atlas’s relatively detailed, ranked six-category classification. This ranges from no reported storage to storage for feasting and redistribution (Murdock, 1967). The six categories actually split along a dichotomous pattern of energy-extraction strategies, distinguishing societies that seasonally utilize stored foods for individuals’ daily energy intake (types 3–5) versus those that do not (types 0–2). On this basis, Keeley’s hunter-gatherer ethnographic sample may be heuristically divided into consistently defined immediate-returns (nIR = 46) and delayed-returns (nDR = 50) storage technology groups (Ingold, 1983; Woodburn, 1988, 1982, 1980). This is important for the following reason. Whatever the cross-cultural diversity in their sociopolitical institutions, social inequality, and wealthproduction practices, delayed-returns foraging societies used storage technologies that seasonally supply a critical portion of their members’ daily energy budgets. This is a necessary—and in many instances, sufficient—condition for coding an ethnographic case as a DR foraging society, to the exclusion of the IR forager categorization. It is likely that many foraging societies have varied in seasonal reliance on storage over years and decades. Here, ethnographic sources provide short-term snapshots that support coding the ith society sampled as either seasonally storage-dependent or not storage-dependent to cover daily calorie budgets. Consequently, a statistical comparison of IR and DR forager population-ecological patterning in Keeley’s cross-cultural sample supports testing a key observation from his original analysis, one that he based only on visual inspection of his data. Keeley suggested that “the higher the intensity of population pressure (i.e., the higher the ratio of population to resources), the more complex should be the economy” (Keeley, 1988). Keeley’s DR subsample carries methodological implications of its own. Including the Siberian Nivkh (referred to as “Gilyak” in Keeley’s study), all of the delayed-returns hunter-gatherers in Keeley’s dataset were part of an extended North American/Circumpolar geographical sphere of foraging societies that seasonally relied on stored food (Fig. 4). Each DR group would have likely had at least sporadic interaction with the nearest other DR groups. The ecological and cultural interdependence of the DR forager sample has impacted the choice of non-parametric statistical methods. This study employs matrix permutation operations, including Mantel tests, in the Vegan statistical package in R (Oksanen et al., 2015). The existence of a geographically extensive DR hunter-gatherer biocultural area, which persisted into the early 20th century, raises the hypothesis—tested below—that storage technologies contributed to a western North American “complex” forager adaptive system that was resilient to agricultural or early industrial ones. Other variables that Keeley carefully coded are also helpful for this re-analysis. In an era just prior to the advent of digital imaging and geographic information systems software, Keeley further used vegetation maps to measure manually the areal extent of primary above-ground biomass productivity in each case’s reported territory. Using standard secondary biomass production rates for each vegetation regime type (Kelly, 1983), he obtained accurate—but also unusually detailed—estimates of edible above-ground ecological productivity for each society’s territory (Keeley, 1995, 1988). Here, I convert the original English units to a metric-system measure: kg/km2/year. Other variables recorded by Keeley and used in this study are human population density (N/km2) and sedentism. Most societies included in Keeley’s sample are also in Kelly’s (2013) database, which provides an independent check of Keeley’s population density estimates (Supplementary Online Materials). Discrepancies appear to involve cases with multiple available estimates; Keeley (1988) noted that, where alternative density estimates were

available, he adopted the highest one, assuming that ethnographic and historic conditions would more often involve depressed, rather than ecologically overshot population levels. The variable sedentism is defined as the number of months of maximum base-camp stay in the winter or rainy season (Keeley, 1995, 1988). The human population density and secondary terrestrial production rate data were transformed to logarithmic (base ten) values. Sedentism was analyzed as a logit-transformed value, because the raw values—in months—measure degree of completion of an annual cycle. Marginal differences in sedentism at the extremes (very short camp stays and nearly fully sedentary, respectively) may have a greater impact on annual resource extraction rates than do marginal differences around the semi-annual point. Finally, inverting Keeley’s index of “population pressure,” I calculated the number of people per kilogram secondary biomass produced per year (N/kg/yr). It is critical to this reanalysis to note the following. This index is not necessarily a measure of Malthusian population pressure. As Marx trenchantly pointed out in Grundrisse (2005), “How small do the numbers which meant overpopulation for the Athenians appear to us!” From a biocultural-evolutionary theoretical perspective, it can be fairly stated that Marx exaggerated the role of social relations of production and political ideology. As important as those factors may be, an interdisciplinary approach would further consider ecological constraints, along with the complexity of family formation, fertility determinants, and intergenerational resource transfers. Nevertheless, different patterns of social organization, ideological systems, and food management technologies—including agriculture, transportation, and storage technologies—can clearly sustain vastly different calorie extraction rates and human populations, with prevailing productivity determinants (latitude, temperature, precipitation, and geomorphology) remaining roughly constant. Paraphrasing Marx, if we state, “How small do the numbers which meant overpopulation for the Paleoindians appear to the Shoshone or Paiute!” then the annual population:biomass production ratio could just as well be a measure of resource-extraction efficiency. Alternatively, if we frame the issue, “How small do the numbers which meant overpopulation for the Shoshone or Paiute seem to us today!” then we may expect to find indications of pressure on resources. Re-examining Keeley’s data set, organized into the IR and DR subsamples, can shed light on the respective roles of innovation, efficiency, and population:resource imbalances in shaping or constraining variation in biocultural niche and demographic elasticity. 5. Results, part 1: evidence for a delayed-returns foraging niche Delayed-returns foraging appears to have evolved to constitute a distinct, higher-efficiency biocultural adaptation—when compared to immediate-returns hunting and gathering. Thus, the first hypothesis—that of DR-IR niche difference—is supported. The pattern illustrated in Fig. 5—now explicitly teased out of Keeley’s dataset (compare with Keeley, 1988, Figs. 1 and 2)—meets a basic ecological expectation. DR population densities self-organize relative to biomass productivity at predictably higher levels than do IR ones. The primary axes for the log:log correlations (power-law relationships) between population density and secondary terrestrial biomass productivity follow roughly the same slope for the DR and IR subsamples, alike (Fig. 6); however, the DR primary axis follows a significantly higher population-density cline (see Fig. 5). This ecological self-organization pattern is contrary to what the second hypothesis—that of DR-forager positive populationelasticity—predicts. Failing to support the second hypothesis, it appears that DR hunter-gatherer demographic systems tended to reach and equilibrate at negative population-growth elasticity. Mantel test results confirm that the slopes and correlation coefficients for the log:log population density:biomass productivity comparisons are highly statistically significantly greater than zero (Table 1). In addition, the IR-DR distinction alone explains a highly significant, 7

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Fig. 5. Relationships between secondary above-ground annual biomass production and hunter-gatherer population density in immediate-returns and delayed-returns foraging societies. The dashed lines show the OLS best-fit lines through the IR and DR subsamples, respectively.

5 × 10−7 people per kg secondary terrestrial biomass per annum (N/ kg/yr). Initially proposed by Keeley (1988) as a metric for population pressure, the population:secondary above-ground productivity ratio is an intuitively satisfying, unidimensional measure of an omnivorous foraging society’s capacity to extract edible biomass and convert it into survival and reproduction. Visual inspection of Fig. 7 indicates that each subsample distribution has marked upper and lower tails, which do not follow the semi-log linear clines; a small handful of forager societies—in the IR and DR categories, alike—exhibit unexpectedly low or high population:ecological productivity ratios (Table 2; these societies are also labeled in Figs. 5 and 6). Excluding the tails, 89% of the IR

substantial amount of the overall correlation between secondary biomass production and forager population density (see Table 1). The well-separated IR and DR population density clines are further highlighted in Fig. 7. Here, a simple visual method (identifying frequency distribution tails) indicates that, for 89–90% of the respective cross-cultural subsamples, the ethnographically observed population densities behave as normal random deviates from the ordinary leastsquares regression lines, with respect to secondary terrestrial biomass productivity (see Figs. 5 and 6). Illustrated in Fig. 7 are the cumulative frequencies of log-transformed population:ecological productivity ratios for the 46 IR societies and 50 DR societies, sorted into bins of

Fig. 6. Relationship of z-transformed values of log(secondary terrestrial biomass production) and log(population density) for the IR (n = 46) and DR (n = 50) samples, respectively. The red dotted lines show the 2-standard-deviation errorlevel for the (solid red) OLS best-fit line of the IR sample only. Overall, this plot highlights the strong right-hand skewness of the IR sample secondary biomass productivity values, suggesting an over-representation of IR societies in higher-productivity lower-latitude environments. The plot also highlights that all but five DR societies exhibit population density deviations within the 2-sd error range predicted by the IR sample, reflecting—in large part—the similar OLS slope values for the two groups. However, these five pseudo-outliers drive relatively strong negative kurtosis of the DR sample’s population density distribution (see Supplementary Information: S1A Table). The 10 numbered cases also have outlying population:biomass-productivity ratios, as identified conservatively in Fig. 7. The identities of the numbered cases are given in Table 3. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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The modeled linear relationships among Log(Secondary Terrestrial Biomass Production), Log(Population Density), Log(Population:Secondary Biomass Production ratio), and Logit(Sedentism) are of the form Y ~ X, where X and Y are n × n pairwise dissimilarity matrices for values of the respective independent and dependent variables x and y. The partial correlations are of the form Y·Z ~ X·Z, where Z is the pairwise dissimilarity matrix for fixed variable z. The matrix correlations (measured as Pearson’s r) and their significances were obtained with the mantel and mantel. Partial functions in the vegan package for R (Oksanen et al., 2015). Very highly significant results are shown in bold-italic. 2 The 99% quantile value for the upper-tail of the distribution of Pearson product-moment correlation coefficients, r, obtained by random permutations of the data matrices. Highly significant comparisons have observed r-values that are much higher than the 99% quantile in the simulated distribution. 3 p-values for the observed data, when compared to the Mantel-test simulated distribution. All but one test resulted in zero simulated r values higher than the observed. The model log(Population Density) ~ log (Secondary Terrestrial Production) in the total cross-cultural sample (n = 96) yielded 29 out of 999,999 random permutations of the independent variable distance matrix.

≫0.001 0.096 0.170

Log(Population Density) ~ Log(Secondary Terrestrial Production) Log(Population Density) ~ Log(Secondary Terrestrial Production) Partial correlation on IR-DR classification Logit(Sedentism) ~ Log(Pop:Prod ratio) Partial correlation on IR-DR classification

Fig. 7. Semi-log plot of cumulative frequency versus population:biomass-productivity ratios, for the DR and IR subsamples, respectively, organized into bins of 5 × 10−7 people per kg secondary terrestrial biomass per annum (N/kg/yr). The dashed lines show the non-overlapping ranges for population:biomassproductivity ratio values for the DR and IR samples, when graphically identified tails are excluded. This plot illustrates that, within the central ca. 90% of the cumulative frequency distributions, log(population:biomass-productivity) values are distributed highly evenly for both subsamples.

sample closely follows a population:productivity cline; for these 41 non-storage-dependent foraging societies, a best-fit semi-log linear function accounts for 99.5% of observed variation in the population:ecological-productivity cumulative frequency distribution. Similarly, 45 out of 50 DR societies follow a higher population:ecological productivity cline, with R2 = 0.990. In other words, Fig. 7 provides an aggressive graphical “tail-removal” criterion for defining regression outliers, but these only exclude five cases from each subsample. Four out of five outlier DR societies occupy high Subarctic and Arctic territories. These are the four DR societies that exhibit surprisingly low population densities relative to the statistically significant self-organizing pattern, which—as argued above—reflects forcing by prevailing, edible above-ground biomass productivity (see Figs. 5 and 6). Just as Tallavaara et al. (2018) have presented evidence that tropical habitats constrain mobile forager populations, Arctic environments may have been inhabitable, but they likely have had an analogous “extreme-environment” dampening effect on DR population limits. The 86 non-outlier societies—occupying territories whose prevailing secondary terrestrial biomass productivity Keeley independently estimated—exhibit ethnographically recorded population densities with a key feature. They behave consistently as if they were members of random, independent subsamples. Moreover, within these subsamples, the strong self-organization of population:biomass-productivity ratio frequencies confirms that IR and DR forager economic systems were fit to distinct energy extraction regimes. The log-linear trends shown in Fig. 7 document that, within well-defined subsample ranges (see below), a shift from IR to DR niche—holding biomass productivity and economic system constant—yielded non-linear change in labor efficiency. The self-organization of population densities across ecological productivity clines is a robustly documented pattern in the bulk of Keeley’s cross-cultural dataset. With the outliers excluded, the correlations between log-transformed population density and secondary terrestrial biomass productivity give—not surprisingly—higher values for Pearson’s r, when compared with results from Keeley’s entire sample (see Table 1). With the significance evaluated with the Mantel test (999,999 random permutations), the IR subsample (nIR_revised = 41) yields an r-value of 0.756 (p≪0.001). The DR subsample (nDR_revised = 45) yields an r-value of 0.380 (p≪0.001). For the restricted IR society subsample, the population:secondary terrestrial productivity ratio (N/kg/yr) ranges between 5.00 × 10−6 and 3.75 × 10−5. The non-overlapping, higher DR range

1

0.447 0.250 ≫0.001 ≫0.001 0.174 0.165 0.096 0.083 0.002 0.037 0.179 0.531 Immediate Returns Societies (n = 46) Delayed Returns Societies (n = 50) Total Cross-Cultural Sample (n = 96) Logit(Sedentism) ~ Log(Pop:Prod Ratio)

≫0.001 ≫0.001 0.188 0.143 0.663 0.272 Immediate Returns Societies (n = 46) Delayed Returns Societies (n = 50) Log(Population Density) ~ Log(Secondary Terrestrial Production)

p-value3 Simulated r 99% quantile2 Observed Correlation Coefficient, r Sample Linear Correlation Model1

Table 1 Mantel test correlation analysis results for the Immediate Returns and Delayed Returns forager cross-cultural samples.

A.J. Stutz

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Table 2 Hunter-gatherer societies with outlying population:biomass-productivity ratios (PBRs). SOCIETY1

Secondary Terrestrial Productivity (kg/km2/yr)

Population Density (N/km2)

Population: Biomass-Prod. Ratio (PBR) (N/kg/yr)

Residual PBR (N/kg/yr)2

Immediate-Returns 1. Wikmunkin 2. Guayaki (Aché) 3. Andamanese 4. Wongaibon 5. Panamint

82,300 9780 15,500 2980 313

0.195 0.026 0.872 0.195 0.021

2.37 2.67 5.63 6.54 6.81

× × × × ×

10−6 10−6 10−5 10−5 10−5

−6.69 × 10−6 −8.53 × 10−6 4.56 × 10−5 5.28 × 10−5 5.23 × 10−5

Delayed-Returns 6. Bering Eskimo 7. Angmaksalik 8. Tanaina 9. Ingalik 10. Tlingit

2080 2340 1390 1270 1580

0.039 0.078 0.058 0.055 2.870

1.87 3.31 4.17 4.34 1.81

× × × × ×

10−5 10−5 10−5 10−5 10−3

−2.70 × 10−4 −2.58 × 10−4 −2.40 × 10−4 −2.36 × 10−4 1.53 × 10−3

1 The outlying cases are defined graphically as constituting the tails in the respective IR and DR cumulative frequency distributions shown in Fig. 7. The numbers correspond to the cases labelled in Fig. 6. 2 The residual population:biomass-productivity ratio (PBR) is calculated as the observed PBR minus the expected PBR, based on ordinary least-squares models of population density regressed on secondary terrestrial productivity for 41 non-outlier IR societies and 45 non-outlier DR societies, respectively.

is 6.55 × 10−5 to 1.29 × 10−3N/kg/yr. These results further clarify that DR systems constituted an adaptation to a more economically efficient energy extraction regime. They do not support Keeley’s original assumption that DR populations were generally under greater population pressure on resources. Excepting the outliers identified in Fig. 7 and Table 2, the populations constituting a highly diverse sample of immediate and delayed-returns hunter-gatherer societies, alike, were—on average, at least, and within their respective territories—demographically stationary. It is important to point out that this stationary pattern may, in significant part, have been regulated by dispersal or emigration practices. This is consistent with Homo sapiens’ comparatively high positive elasticity of fertility (Jones and Tuljapurkar, 2015) and scaling patterns in mobile hunter-gatherer residential and aggregation group-sizes (Hamilton et al., 2007b, 2007a). In the discussion below, I return to the likely role of dispersal and migration practices in mediating local population levels among DR hunter-gatherers, in particular. IR foragers—again, defined cross-culturally as those hunter-gatherer societies that have not adopted storage technologies to cover calorie budgets on a seasonal basis—appear to exhibit stronger self-organization of their population densities relative to biomass productivity. Assuming that observation error was low, the relatively small residual differences in population density, with respect to secondary terrestrial biomass productivity (see Fig. 5), would indicate that IR hunter-gatherer demography has generally been more constrained by prevailing ecosystem conditions. It is important to caution, though, that DR population density estimates are liable to greater error, when sorting through ethnohistorical documents, archaeological evidence, and ethnographic reports. With similar or smaller territory areas, DR societies tend to have larger—or even much larger—census sizes. In contrast to smaller IR population sizes, inaccuracies in DR census measurements—often dependent on reconciling conflicting ethnohistorical sources (Gamble, 2011)—will generate larger error in demographic measurements, potentially contributing to the lower observed correlation between DR population density and terrestrial biomass productivity. Log-log transformations notwithstanding, this would suggest that the observed DR correlation reported in Fig. 5 and Table 1 is an underestimate. At the very least, DR foraging societies in Keeley’s sample were still significantly demographically constrained by their ecology. Their socio-technological systems exhibit a limit on achievable the energy extraction rates that could feed additional population growth, supporting higher local population densities. To underscore a main result of this reanalysis, The hypothesis of DR positive population elasticity is not supported. Energy-extraction and population growth alike are significantly limited in the DR niche, critically inhibiting the

elasticity of growth in foraging returns. 6. Results, part II: evidence confirming the DR forager adaptive system With his compilation, analysis, and discussion of a comprehensive cross-cultural forager dataset, Keeley (1988, 1995) made a key contribution to research on hunter-gatherers. He marshalled evidence that ethnohistorically documented and ethnographically observed societies tended toward either “simple” or “complex” economic and political poles. Since then, the development of niche construction theory and energy-flow-based food-web models (Laland et al., 2015; Loreau, 2010; McCann, 2011; Mohlenhoff and Codding, 2017; Odling-Smee et al., 2003; de Ruiter et al., 2005) has facilitated clarifying niche characteristics, distinguishing them from adaptive biocultural features. The previous section emphasized the relationship between population density and prevailing edible terrestrial biomass productivity. Self-organization of demographic density across the ecological productivity cline provides a highly significant criterion for identifying separate IR and DR foraging niches. In this section I focus on a reanalysis of Keeley’s coding for sedentism—again, measured as poor-season camp duration. The results help to clarify DR biocultural adaptations, fit to their constructed, relatively high energy-extraction niche. As illustrated in Fig. 8, sedentism significantly supports the seasonal reliance on stored foods, so that the populations constituting DR societies achieve higher densities relative to edible terrestrial biomass production. A nonparametric multivariate analysis of variance shows that (logit-transformed) sedentism and the (logarithmic-transformed) human population:secondary-terrestrial-biomass-production ratio correlate highly significantly with the binomial IR-DR storage distinction (R2 = 0.776, F = 160, p≪0.001; analysis carried out with the adonis function in the “vegan” package in R) (Oksanen et al., 2015). Visual inspection of Fig. 8 might suggest that, within the DR subsample, sedentism correlates positively with the population:secondary biomass productivity ratio. Mantel test results show that this overall DR subsample pattern is not statistically significant (see Table 1). When the five DR subsample outliers (see Table 2) are excluded, a weak correlation is detected (nDR_revised = 45; r = 0.104; p ≈ 0.03). With respect to sedentism, the IR and DR subsamples mainly define non-overlapping bivariate clusters. These results generally confirm Keeley’s original observation that the relationship between population density and sedentism is “mediated by dependence on stored foods” (1988, 404). The minimally necessary defining feature of delayed-returns foraging—food storage to cover seasonally periodic shortfalls in daily energy budgets—is itself a 10

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Fig. 8. Relationship between sedentism (months of annual base-camp occupation stay) and human population:secondary biomass production ratio for the DR and IR society samples. Secondary biomass production provides a baseline index of edible terrestrial food resource production. The bold markers show the respective arithmetic means for the DR and IR samples. The range bars show the sample maxima and minima around the means.

cultural practice that would have contributed to niche construction, shaping fit to a higher-energy ecological role. However, storage involves patterns of labor mobilization; technological products and built environments; land tenure ideologies; and practical work, consumption, and social-interaction rhythms that—in combination and scale—may rarely, if ever, occur in the residential camps of IR foragers. The new statistical results confirm just how strongly sedentary settlement associates with seasonal storage for daily calorie budgets among ethnographically documented foragers. The outstanding questions are, how did nicheconstruction and biocultural adaptation dynamics play out, and what niche-construction role did storage-adoption play in this evolutionary process? Beyond storage and sedentism, Keeley highlighted other organizational features and technological practices that he argued constitute “complex” hunter-gatherer societies and their environments. These include—following Murdock’s (1981) Atlas of World Cultures terminology—“classes based on wealth and descent” and “standard ‘valuables’ or currency” (Keeley, 1988, Table 8). He also explored how communityintegrating rituals and landscape management (burning and sowing practices) may have fit into a “complex” foraging pattern (Keeley, 1995, 1988). Here, I emphasize that the IR and DR forager samples actually show overlap in social inequality patterns and community-integrating ritual practices (Table 3). For example, 18% of the DR subsample exhibit only limited wealth distinctions (Fig. 9). Whereas sedentism is unambiguously tied to seasonal storage for daily energy budgets, sociopolitical and resource-management complexity are not restricted to DR foraging societies. A few IR societies in Keeley’s sample have culturally institutionalized, substantial wealth inequality; several engage in fire management and quasi-horticultural sowing (Keeley, 1995). The intricacy of hunter-gatherer economic, political, and cultural diversity has been thoroughly treated by Kelly (2013), revealing that the “simple”-“complex” terminology describes poles on a foraging spectrum; as a dichotomous classification, it insufficiently describes known forager variability. That said, DR societies—as a group—do exhibit a highly significant statistical associations with regular (as compared to ad hoc or sporadic) rituals and institutionalized production and maintenance of wealth inequalities, including those involving heritable, ranked chiefly and commoner lineages (see Table 3). Taking into account the restricted geographic distribution of the DR subsample societies (see Fig. 4), I suggest that a dynamical niche construction framework (Odling-Smee et al., 2003) supports a hypothesis consistent

Table 3 Two-tailed Fisher’s exact test (FET) results of cross-tabulations for storage practices, group-integrating ritual practices, and institutionalized wealth inequalities in foraging societies. A. p-value(FET) = 2.77 × 10−8 Immediate Returns (n = 46) Delayed Returns (n = 50) B. p-value(FET) = 8.34 × 10−15 Immediate Returns (n = 46) Delayed Returns (n = 50) C. p-value(FET) = 1.57 × 10−12 Sporadic Ceremonies (n = 45) Regular Ceremonies (n = 51)

Sporadic Ceremonies (n = 45) 35 10

Regular Ceremonies (n = 51) 11 40

No Wealth Distinctions (n = 52) 43 9

Wealth Distinctions (n = 44) 3 41

No Wealth Distinctions (n = 52) 41 11

Wealth Distinctions (n = 44) 4 40

Fig. 9. Cross-tabulation counts for wealth inequality versus foraging economic system. While limited wealth distinctions are especially strongly associated with IR foraging systems, DR societies show some variability in wealth inequality.

with this statistical link. Institutionalized wealth and status inequality, often alongside regular community-integrating rituals, were key 11

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Fig. 10. Box-and-whisker plot of log-transformed secondary terrestrial biomass production rates for habitats occupied by IR and DR societies, respectively. The plot shows that, while the median DR value is slightly higher than the IR one, the overall DR range spans only a subset of the IR ecological productivity range.

argument about foragers’ role in post-Pleistocene biocultural evolution. The long-term emergence of sociopolitical complexity has been about hunter-gatherers, not only about agriculture-based cultural systems (Arnold et al., 2015; Fitzhugh, 2003). At the same time, only agricultural production—often associated with livestock grazing and management or large-scale fishing technologies—has sustained recurrent, millennial-scale cycles of innovation, carrying-capacity increase, and population growth (see Fig. 3). The results presented here suggest that DR forager societies could only have indirectly contributed to positive population elasticity, via political fissioning, raiding and slave-taking, or emigration.

features mediating sedentary settlement and the adoption and development of storage practices, further shaping the emergence of a widespread, resilient DR foraging niche in western North America (see Fig. 4).

7. Discussion The statistical reanalysis presented in this study brings into focus well-defined ecological differences between delayed-returns and immediate-returns foraging societies (Woodburn, 1988, 1982, 1980), while simultaneously clarifying insufficiencies in Keeley’s (1995, 1988) “simple”-“complex” dichotomous framework (see extensive consideration of this topic in Kelly, 2013). Across areas that hunter-gatherers continued to inhabit into the 20th Century, many IR societies maintained resilience across five continents and multiple major islands. While the DR-occupied area was much more restricted geographically, the situation looks different when we measure habitat in terms of secondary terrestrial biomass availability. In this dimension, IR and DR foragers often tapped similar levels of above-ground terrestrial ecosystem productivity (Fig. 10), albeit at different levels of labor efficiency. However, in agreement with Binford’s observations, Keeley’s dataset suggests that—among human foraging systems—only IR systems have recently occupied the most productive tropical and subtropical ranges of terrestrial productivity gradients (Binford, 2001; Johnson, 2014, 2008; Keeley, 1995, 1988). The analysis presented here shows that, nevertheless, in many terrestrial environments, IR and DR foraging systems can be alternative sustainable energy-extraction states. In comparison with IR foraging systems, DR storage and settlement adaptations are fit to an energetically distinct niche, with more intense human-human and human-environment flows of energy, matter, and information. Storable foraged foods ultimately limited population growth in more sedentary DR hunter-gatherer societies, implying a pattern of population regulation, likely influenced by a range of “positive” and “negative” checks (sensu Malthus), but also involving emigration or occasional group fissioning and violent conflict over territorial tenure. The finding that DR foraging systems generally cannot achieve sustained positive elasticity of population growth qualifies a key

7.1. Delayed-returns foragers: population inelasticity, encapsulation, and biocultural resilience Woodburn developed his ideas about DR hunter-gatherers in a key paper (1988), arguing that spatially fixed food resources would have imposed ecologically rigid limits on the energy available to DR huntergatherer populations, while also heightening the cost incurred when groups failed to defend those staple foraged foods. This assertion is generally supported by my reanalysis of Keeley’s data (see Figs. 5 and 6). It is further consistent with Woodburn’s expectation that DR systems—driven by the ineluctable importance of defending fixed wild resources—achieve high energy-extraction rates and population densities via increased sedentism (see Fig. 8). In such an ecological context, it would have been organizationally effecitve for DR foraging societies to practice regular community-integrating ceremonies and maintain greater within-group status and wealth inequalities, when compared with IR hunter-gatherers. With highly ritualized social integration, institutionalized collective action and centralization of wealth among elites, DR societies would have often gained economies of scale in capturing and preparing food for storage, implementing exchange of prestige goods, and organizing military action (see also Arnold et al. 2015; Keeley, 1988, 1995). In his critical consideration of DR foragers, Woodburn (1988, 1980) further argued that, when prehistoric mobile hunter-gatherers initially adopted sedentary settlement and storage, they would have been vulnerable to intergroup territorial competition. He suggested that early 12

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occupied a well-defined, relatively high-energy-extraction-rate niche, diverging distinctly from the immediate-returns hunter-gatherer niche. Like the lower-extraction-rate IR niche, however, the DR niche constrained the demographic growth elasticity of its constituent forager populations. This finding shifts theoretical focus decisively away from population pressure, which Keeley—among other key proponents (Cohen, 1977; Rosenberg, 1998, 1990)—saw as a largely isolated causal factor, driving major changes in hunter-gatherer food management, settlement, and socio-political complexity. I have suggested that the salient question, instead, is about Holocene niche diversification and its systemic, complex ties to biocultural adaptation, non-equilibrium population dynamics, and biopolitics. This emphasis on non-linear, variably enriching and disruptive biocultural evolution builds on recent work on complex hunter-gatherers (CHG). Arnold et al. (2015) persuasively argue and support the point that hunter-gatherer-fishers—and not only farmers and herders—evolved paths to complex, hierarchical political organization, with hegemonic rule and institutionalized inequality. They state that “a variety of dietary regimes are associated with the emergence of institutionalized political complexity. Rather than diet, it is the ways people integrate and use labor that demands our attention” (Arnold et al., 2015, 248). The results presented in this study indicate that our attention should not only fall on diet; nor should it only focus on the mobilization, organization, and use of labor. We must also explicitly consider the ways that people form families; invest in reproductive effort, transferring social, symbolic, and embodied capital to offspring and kin; and make decisions about migration. The evidence for widespread demographic inelasticity in the IR and DR niches alike entails something else. It suggests classic Malthusian population regulation, likely combined with variable emigration, group fissioning, and territorial expansion via economic intensification and warfare (Codding and Jones, 2013). We thus need to investigate how demographic behaviors and processes articulate with political and ecological ones (Figs. 11 and 12), ultimately involving systemic feedbacks with niche construction and niche diversification (Figs. 13 and 14). For this same reason, we further need to consider how family formation, intergenerational transfers, and migration behaviors interact with heterogeneity in frailty

DR foraging societies would have likely become encapsulated—that is, marginalized and, eventually, coopted or violently taken over—by emergent agriculture-based political systems. The latter would have had greater elastic capacity to transform territory held into territory yielding edible calories. However, ethnographically documented DR hunter-gatherer societies were concentrated across a large swath of western North America, with archaeological evidence for the prehistoric emergence of sedentism, storage, and sociopolitical complexity in coastal and interior territories, alike (Arnold et al., 2015). This clearly belies Woodburn’s theoretical suggestion that—other things being equal—DR foraging societies should be evolutionarily transient. The recent geographic distribution of DR foraging societies has likely been influenced by the critical availability of mass-harvested, storable aquatic or forest resources (Kelly, 2013). At the same time, it appears that in the western North American super-region—along with an adjacent zone that extended into a higher-latitude ring from eastern Siberia to eastern Greenland—niche construction and adaptation feedback-processes resulted in a complex, resilient mosaic of IR and DR foragers. This reanalysis of Keeley’s dataset highlights how the prehistoric development of sociopolitical complexity in the western North American super-region was an important instance of Holocene biocultural evolution. At least several centuries prior to Spanish contact, a resilient DR foraging niche emerged, co-evolving with new sociopolitical institutions (cf. Arnold et al., 2015). The ethnohistoric and ethnographic sources informing Keeley’s dataset date to the later 18th, 19th and early 20th Centuries. Although post-1492 globalizing developments have continued to impact the descendants of indigenous precontact populations across the Americas, the results presented here indicate that the western North American DR adaptation-niche biocultural system exhibited a certain—arguably, remarkable—resilience. European contact drove overall indigenous forager population declines through pandemic or epidemic mortality, violent conflict, territory loss, and dispersal (Fitzhugh, 2003; Gamble, 2011). Still, many socially bounded DR groups and polities survived or emerged through ethnogenesis, having at least partially recovered local population density-levels. The results highlighted in Figs. 5 and 6 are consistent with DR niche resilience, which would have supported self-organization of polity-scale population sizes, relative to prevailing secondary terrestrial biomass productivity. This is not at all to diminish evidence for the catastrophic human impact of European contact on indigenous American societies and the populations that constituted them. On the contrary, the results presented here highlight how cultural resilience is an important factor to consider in understanding encapsulation and disruptive, often violent biocultural expansion processes, both in the recent and prehistoric past. This perspective should provide new avenues of inquiry into other cases of complex hunter-gatherer niche construction and biocultural resilience, including the Jomon in the Japanese archipelago, the Kuril Islands, the Scandinavian and Baltic Late Mesolithic and early Neolithic, the western Iberian Mesolithic, and the Florida Gulf Coast (Ashley and White, 2012; Fitzhugh et al., 2016; Habu, 2004; Hutchinson, 2004; Marquardt, 2001; Nilsson Stutz, 2014, 2003; Stjerna, 2016; Stutz, 2012). 7.2. Post-pleistocene biocultural evolution, niche construction, and niche diversification

Fig. 11. Basic model of a non-linear, sigmoidal labor productivity function as a response to population size, illustrated relative to the constant, linear aggregate-consumption function. Although the right-hand intersection of the two functions is a stable equilibrium point, the overall space in which production exceeds consumption defines the possibilities for allocating resources to influence relationships and exercise power. Under a given cultural system of biopolitical inclusion, collective action, cooperation, reciprocity, obligation, and coercion, the population may actually equilibrate at the maximum point of excess production. This population level is labelled S1. Importantly, the social management of surplus production is critical to maintaining the non-linear sigmoidal production function, which depends on cooperation, division of task labor, and economies of scale. Adapted after Lee (1986, Fig. 1).

Since Keeley (1988) published his initial analysis, key lines of crosscultural research on foragers have remained in the forefront. Comparative work has mainly continued to focus on how prevailing environmental productivity has affected hunter-gatherer demography and population density and, in turn, how the latter has related to technology and socio-political institutions (Binford, 2001; Collard et al., 2011; Johnson, 2014, 2008; Tallavaara et al., 2018; Vaesen et al., 2016). The re-analysis of Keeley’s dataset presented here supports the biocultural evolutionary hypothesis that delayed-returns foragers constructed and 13

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Fig. 12. Superimposition of higher-productivity/larger-population functions over the optimal biocultural population level shown in Fig. 11 (population point S1). Higher energy-extraction-productivity can emerge as organizational and technological innovations are adopted, mediated by changes in biopolitical strategies and institutions, from community-integrating ritual to organized raiding and warfare, and from kinship and gender-based decision-making practices to the establishment of chiefly lineages and rule. Even if higher mortality marginally depresses the slope of the aggregate consumption function, the non-linear behavior of the higher-productivity function dramatically widens the population range—along with possible biopolitical and sociopolitical strategies—in which excess production may be exploited. This provides a theoretical account for why Keeley’s DR subsample exhibits more diversity in wealth inequality than does the IR subsample (see Table 3 & Fig. 9).

Fig. 14. A hypothetical model of post-Pleistocene niche diversification in this niche construction space.

and survivorship patterns, especially under conditions of eco-cultural niche alteration and bifurcation. This is a complex but critical intersection. Here, the biopolitics of work, access to social networks, utilization of land and resources, family-building, migration practices, and culturally sanctioned violence meets the bio-economy of feeding, physical activity, growth, infection, injury, inflammation, healing and maintenance, reproduction, aging, and dying. Moreover, bio-economics encompasses the interface between the body and its surroundings, thoroughly mediating how populations impact their prevailing niche, from institutionalized patch-engineering practices to indirect enrichment or depletion impacts. As illustrated in

Fig. 13. Heuristic representation of biocultural niche construction space, highlighting eco-cultural, biopolitical, and bio-economic dimensions. 14

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social-boundary monitoring (Kelly, 2000), and indirect ecological effects on resource productivity or accessibility (Asouti et al., 2015; Stiner, 2001; Stiner and Munro, 2002; Stutz, 2014b) (see Fig. 14).

Figs. 13 and 14, biopolitics and bio-economy may be heuristically, efficiently described as constituting a biocultural niche space encompassing immediate returns hunter-gatherers, delayed-returns huntergatherers, and delayed-returns agriculturalists. An important step for future research, I argue, is to model niche-diversification dynamics, not only in relation to population dynamics—involving emergent positive population elasticity in agricultural systems—but also in the multiscalar biopolitical and bio-economic niche space.

8. Conclusion: reflections on population dynamics, niche diversification, and biopolitics This study’s theoretical point of departure has been in the interrelated phenomena of biocultural niche-diversification and population (in)elasticity. Keeley’s cross-cultural forager dataset has provided a set of observations robustly supporting the hypothesis that, under similar levels of terrestrial above-ground biomass productivity, delayed-returns foragers extract energy and nutrients at a higher rate than do immediate-returns hunter-gatherers, leveraging that energy gained into higher sustainable population densities. Still, the picture of huntergatherer niche bifurcation—into distinct IR and DR patterns—must be understood in the context of demographic inelasticity and population regulation. Moreover, as modeled in Fig. 14, the hunter-gatherer inelastic niches must be investigated in relation to positively elastic agricultural niche construction. In order to develop theoretical approaches to niche construction and niche diversification, I have argued that a joint biopolitical and bio-economic framework can help to explain the interrelated, complex social, population, and environmental dimensions of organizational and technological development, demographic change, and ecological impacts that mark post-Pleistocene human history. I have introduced a focus on the bio-political dimensions of inclusion and exclusion in social action that have bio-economic payoffs or costs at multiple life-history scales. It is important to note that such an approach to biopolitics can be considered in comparative primate ethological perspective. My focus has further been on the complex human bio-economy. On the one hand, the bio-economy encompasses variation in somatic allostasis and well-being across our extended life-history pattern (Edes and Crews, 2017; Ellison, 2001; Gurven et al., 2016; McEwen, 1998; Wood, 1998). On the other hand, it involves energy extraction and impact on the wider eco-cultural niche. In the short term, the biopolitics of mobilizing collective action, cultivating relationships and alliances, and handling conflicts can interact with the bio-economy of managing daily energy flux, energy balance, stress, infection, and inflammation. At longer microevolutionary timescales, biopolitical practices can drive variation in the intergenerational transfers of genes and broader epigenetic conditions, including culturally structured institutions and embodied capital (see Figs. 13 and 14). This involves an intricate, nonlinear coupling of family-formation, well-being, and biopolitics. In this dynamic biocultural systems context, diversification of foraging and agricultural niches would have been a significant part of local or regional perturbation and enrichment processes in the Holocene. The non-equilibrium coupling of biopolitical and bio-economic systems with the wider biosphere is generally key for understanding the joint development of extensive social inequality and environmental impacts in recent human systems. Further investigating these dynamics will be key for understanding the dramatic trajectory of post-Pleistocene biocultural change, demographic growth, and niche alteration.

7.3. On biopolitics: managing inclusion and exclusion in bio-economic context In political philosophy, the term biopolitics has focused on hegemony-production practices and institutions in historical and contemporary settings, from ancient Athens to today’s systems of governing, constituted through complex medical, incarceration, surveillance, legal, and information-management systems (Agamben, 2016, 1998; Foucault, 1990). The biopolitical framework emphasizes the deeply embodied and intercorporeal dimensions of power production. While the theoretical construct is apt for analyzing and comparing hegemonic systems of governing in large-scale, complex societies, the very notion of biopolitics is a heterogeneous and changeable social phenomenon. For example, rites of passage and feasts cast the social order as symbolically coherent, constituted by corporeally affected, affectively engaged members (Nilsson Stutz, 2003; Stutz and Nilsson Stutz, 2018). To broaden Foucault and Agamben’s concept, biopolitics is more generally about social action that aims to influence or determine participation and exclusion. Biopolitics may be defined as involving ritualized collective action, on the one hand, and mundane social judgment, exchange, social-bonding, and violence practices, on the other, marking focal or targeted individuals or groups bodily, in order to structure participation and decision-making over bio-economic strategies. Iterated biopolitical behaviors may reflect previous bioeconomic outcomes—for example, access to calories and nutrients, change in biological well-being, development of ego’s embodied capital, and transfer of inclusive embodied capital to offspring and other close kin. Biopolitics—extended as a theoretical concept applicable more generally to the evolution of cooperative territorial defense, cooperative foraging, and food sharing—is fundamentally about who gets a chance to influence relationships, habits, and learned techniques affecting the bio-economics of energy balance, energy flux, and wellbeing within the group. It is thus a multiscalar temporal, spatial, and social framework. It is aimed at understanding variability in those animal social systems that are constituted by feedbacks among relationships and networks; embodied social interactions, embodied narratives, and memory; and heterogeneity in bio-economic outcomes. In the human case, socially integrating rituals are biopolitical, even when they do not involve outright violence and physical exclusion or separation from focal individuals or groups. While ritualized violence may arguably become more conspicuous for producing social order and power in DR societies, the broader definition of biopolitics encompasses many ritual and social judgment practices—including those common in IR and DR societies alike—promoting participation, collective action, and biological well-being. These include gift-giving, ecological information-sharing, story-telling, dancing and trance rituals, healing rites, marriage discussions and negotiations, and collective hunting or harvesting, as well as feasting. Such practices have direct and indirect impacts on bio-economic processes at the bodily scale, in turn, shaping survivorship, kinship networks, marriage alliances, emergency decision-making, and conflict adjudication. They can also influence the ecocultural niche at the landscape scale, as labor-intensive patch engineering can mediate biopolitical inclusion, while also raising sustainable energy and nutrient extraction rates (Mohlenhoff and Codding, 2017). The feedbacks among biopolitical practices and bio-economic outcomes likely further shape hierarchically organized or heterarchically differentiated institution-construction (Crumley, 1995),

Declaration of Competing Interest The author declares that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments The author is grateful to Paul Hooper, Eleni Asouti, and an anonymous reviewer constructive critical feedback that has improved this article. Hanne van der Iest provided invaluable assistance with R. The author further acknowledges Jaimoe’s enduring support. All 15

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insufficiencies and errors are the author’s responsibility.

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