Non-Nested Hierarchy and the Human Niche

Biocultural evolution in our genus has largely involved dynamic, often non-equilibrium mutual perturbations between the complex, hierarchically structured environment and hierarchically structured cognitive sense of landscape, time, and social identity.

In working on the Human Niche Overview post, I spent some time refining the figure at left. In it I tried to characterize aspects of the human niche encompassing the social and the cultural, so I could provide a succinct summary of niche-adaptation co-evolution as biocultural evolution in the genus Homo. I’ll go into more detail about the “Adaptation” side of the figure in later posts. In this post I focus on the unusually complex–but rarely acknowledged–hierarchical structure of the human niche. The hierarchical dimensions of our niche arguably drive what I described as (o.k., a hyphenation bonanza here) the “recurrent non-equilibrium niche-adaptation evolutionary dynamics” that characterize biocultural evolution over the long-term. For now, concerning the “Adaptation” side of the figure, I would like you to think a bit about why I have made the leap and very specifically included as a distinct human adaptation cultural symbolically structured, embodied representations that contextualize ego in society, landscape, and time.

Now, let’s focus on the niche side of the evolutionary dynamic. Tooby and Devore’s (1987) “cognitive niche” is certainly evocative in getting us to think about niche as encompassing the social and symbolic environment. Recently, Steven Pinker (2010) and Andrew Whiten and David Erdal (2012) have provided elaborations of the idea. The problem with this approach, I think, is that “cognitive niche” tends to blur niche and adaptation.

So in the figure above, I’ve tried to build on the “cognitive niche” approach by making clear what’s niche and what’s adaptation. On the niche side of the figure, I ordered key features or dimensions, so that early hominin–and even modified Miocene ape–aspects of niche that the genus Homo inherited are shown on the bottom. The basic evolutionarily primitive aspects of the genus Homo‘s niche are thus terrestrial, heterotrophic, and extractive. (In my Foundations of Behavior course, I use the mantra “terrestrial, omnivorous, extractive niche” to help student stay focused on the general environmental structure shaping selective forces on biological variation over six or seven million years of hominin evolution. This year–and it’s taken years, for some reason–a few of my students working in a study group hit upon the “T.O.E.” acronym. Not a bad mnemonic for also integrating niche-adaptation co-evolution involving bipedal locomotion.) The social structure of early hominins, including that of australopithecines and earliest Homo, up to ca. 2 million years ago, remains susbtantially the subject of speculation (Chapais 2013). But theoretical arguments and archaeological evidence do support the conclusion that later, with the emergence of Homo erectus around 2 million years ago in Africa, the human niche underwent a long-term trend of increasing social intensity and complexity (Gowlett et al. 2012). From birth to senescence, members of the genus Homo would have joined, exploited, negotiated, and been challenged by larger social networks, with more complex and frequent clique and alliance shifts, than our earlier australopithecine ancestors and extinct relatives experienced. Certainly, a dynamically evolving but evolutionarily derived aspect of niche in Homo was–and is–that of social intensity.

But it is more than just social intensity. There’s another, rarely recognized–but potentially illuminating–pattern. It involves multidimensional hierarchical structure…on both the niche and adaptation side of things. This requires a bit of explaining. Hopefully, though, the pay-off will be a more useful framework for investigating the emergence of (o.k., here it is again) recurrent non-equilibrium biocultural, niche-adaptation co-evolution dynamics in our genus over the past 2 million years.


Quickly, an upfront acknowledgment: After searching occasionally through ecology articles and texts, over a period of years, trying to track down a serious general theoretical treatment of hierarchical organization in living systems (hierarchy and scale aren’t the same thing, and there’s a lot more on scale relationships in ecology than there is on hierarchy), I finally realized that it would help to search directly for “hierarchy,” rather than “scale” or “complexity.” I’m stubborn, if not efficient, in my work, but when I got it right, I finally found Allen and Star’s (1982) … wait for it … Hierarchy: Perspectives for Ecological Complexity. Anyway, when I talk about filtered dynamics between systemically related structures in the human niche, I’m relying 100% on Allen and Star’s explanation that non-nested hierarchical relationships are best modeled as one system component asymmetrically dominating the other(s). Higher levels in a non-nested hierarchy tend to filter out information transmitted from lower levels, so that they respond in a less sensitive way. Lower levels filter less, and thus, they are more influenced by the higher levels. An example would be how somatic cells have a non-nested hierarchical relationship below tissues and organs. Although tissues and organs influence individual cells much more than vice versa, there are definitely situations (e.g., cancerous growth) where higher integrated tissue or organ structures and functions are sensitive to information from cells. Moreover, with metastasizing cancer, the cells are not strictly nested within the tissue or organ structure. Another example that Allen and Star highlight is how overlapping, long-lived generations constitute a non-nested hierarchical system, in which older generations have a net greater influence on the fitness of younger ones, in a non-nested, asymmetric pattern. In fact, inspecting the form of Robert May’s classic model of intergenerational lags in fitness effects, Allen and Star point out that May’s formal model has the form of an analog acoustic filter in sound engineering! In general, the concept of non-nested hierarchy couldn’t be more helpful for explaining how natural systems could gradually evolve more complex integrated structures. How this applies to the human niche–specifically with spatial, temporal, and social non-nested hierarchical structures–will become clearer with some of the examples below (I hope).


I’ll start with a well-understood connection to my main area of expertise, Paleolithic archaeology. Archaeologists Glynn Isaac and Lewis Binford were especially influential in integrating ethnographic information about hunter-gatherer societies with research on our Paleolithic prehistory, and they implicitly emphasized the hierarchical structure–in spatial, temporal, and social dimensions–of small-group daily foraging combined with home-base/mobile camp food preparation and sharing. Isaac’s main point was that in human evolution, along with the evolution of stone-tool-making and hunting behaviors in the late Pliocene or early Pleistocene, the foraging “home base” would have been at the center of a complex behavioral nexus supporting cooperative hominin groups. Hunting and gathering behaviors are best understood not just in terms of searching for and getting food, but also bringing food back to home bases. Thanks to Isaac’s insights and arguments, we almost take for granted this cooperative-foraging/food-transport/sharing behavioral system as obviously constituting an evolutionarily emergent foundation of human society. But this system is subtly complex. Binford further helped to put hunter-gatherer mobility patterns into evolutionary perspective. Frequent formation and movement and re-establishment of residential camps can structure socially based hominin adaptations over larger foraging territories. Thus, the hierarchical structure starts to come into focus. We tend to have a multi-level hierarchical pattern in human hunter-gatherer experience–mapped out in space, time, and social networks. Here, daily routines are hierarchically structured … and then daily and seasonal patterns of residential moves through territories and with a larger configuration of allies and kin constitute the annual round at the next hierarchical scale.

Let us consider the hierarchical structures of this behavioral system in ethnographically documented hunter-gatherers more carefully. Returning our focus to niche-adaptation co-evolution, might we be able to separate out what’s niche, what’s adaptation, and how they might have influenced each other? I would suggest that the hierarchical structures interconnecting humans across the landscape, through time, and in varied social network configurations have constituted an aspect of niche that imposes clear selective pressures on embodied and social cognitive functions. In turn, because the selective pressures are on embodied and social cognitive capacities, the resulting symbolically structured experience of landscape, time, and social relationships can become part of the niche itself. Let’s consider the spatial, temporal, and social aspects in turn, just in the context of daily foraging, food transport, and processing/consumption routines.

First, spatial hierarchy. Even in highly mobile hunter-gatherer societies, the daily routine is recognizable. Food search and acquisition involves following a novel path (Yellen 1977), potentially covering several kilometers from the home base and back. Yet, the home base is a spatially fixed landscape anchor, at least on a time scale of days, weeks or months. Spatially, the home base strongly “filters” the distances and locations involved food-search, food-capture, field processing, and transport behaviors. In turn, impact on food resources in the area around the camp dynamically filters cooperative decision-making to stay or move camp. However, the strength of the filtering effects tends to be asymmetric, so that social central-place food processing and consumption maintains a hierarchical influence over foraging behaviors. And importantly, the hierarchical spatial relationship between home base location and area covered in foraging and food transport is not strictly nested. Groups can establish a seasonal camp by a nut grove or tuber-rich lake shore, so that the hierarchical camp-foraging relationship can temporarily disappear for a matter of days or weeks, at least in certain seasons of the year. In early Stone Age prehistory, it would have been more common–in many environments–for hominin groups to snack more while foraging (eating as they went), so that the filtering effect of the mobile residential camp on foraging and transport would have been weaker and more variable. Still, this spatial hierarchy involving foraging behaviors diverges from the eat-as-you-go pattern we see across the rest of the primate order, including behaviors exhibited by chimpanzees and bonobos, our closest living relatives.

Second, home-base or residential-camp foraging involves an intrinsically embodied socio-temporal hierarchy, in that food acquisition and consumption are thus more often substantially separated (of course, ethnographically documented hunter-gatherers snack on raw or rapidly processed foods in the field, but most food is consumed after transport to the residential camp). Delayed consumption is a conspicuous, altruistic behavioral adaptation. And again, it structures the human niche in terms of temporal hierarchy within daily embodied routines. The fitness benefit of such altruistic behavior–despite carrying risks of inviting aggressive, continuous, or simply emotionally irritating theft or begging–comes in terms of the recurrent reciprocity payoffs of sharing food at the residential camp (Winterhalder 1986). But consider the social implications of this temporal daily-routine cycle, with leaving and returning to the base camp. With what would presumably be a fission-fusion process on this timescale of hours, smaller foraging groups would tend to include close allies or kin, and time spent would involve mainly cooperative behavior. Episodes of attempted free-loading, cheating, intimidation or attempted theft during a foraging trip would have a greater cost for all involved. Foraging group members would generally be working harder, be hungrier, and to the extent that cooperation improves food search and acquisition efficiency, any attempt to free-load or cheat could thus provoke rapidly escalating aggressive conflict. We would expect foraging trips to involve mainly consensus decision-making and cooperation, with more occasional episodes of bitter conflict. In contrast, the larger base-camp experience would be a period of negotation, more complex (and potentially less reliably accurate) information exchange about reputation of many group members, along with recuperation and the experience of satisfying or limiting hunger. In brief, hunter-gatherer routines would tend to have a non-nested (that is, not strictly) hierarchical separation of more focused, consensus-built small group foraging activities, and more dynamic, emotionally variable, socially intense camp experiences. The emphasis on sharing, reconciliation, gossip, consumption, rest, and less relevance for high levels sensory alertness (monitoring signs for prey, predators, or other important opportunities and dangers) entails that time in camp is less sensitive to what happened on each and every foraging trip. It should be clear that, on the one hand, this is a non-nested hierarchical structure of foraging and consumption behavior that is evolutionarily uniquely derived compared to other primates, but on the other hand, the emphasis is on “non-nested.” As such, the hierarchical temporal structuring of experience as part of the niche in hominins is something that must have evolved gradually over time. This is a topic worth exploring in much greater depth! What was the timing, tempo, and mode of this particular socio-temporal aspect of hominin niche construction?


If we begin with this common space-time-social-configuration hierarchical structure to daily routine in human foraging societies, then we can easily begin to see how space, time, and social interaction exhibit complex hierarchical structure at higher scales. We can even consider that common cultural representations may often emphasize nested hierarchical ideals, and these can actually serve as ideological symbols in negotiating exchange, allegiance, future plans, or declarations of shared identity. In other words, members of a group may think or speak of the boundaries of their foraging territory, with landscape beyond that imagined boundary being, by definition, the rest of the universe, so that logically, the nesting relationship is: our total foraging territory and other hunter-gatherer groups’ total foraging territories fit into the larger conceptual category of the universe. But in reality, group composition, cultural representations of group identity, and the position of asserted, desired, or agreed-to territorial boundaries all shift. So, embodied routines and experiences interact with cultural representations, tending to produce beliefs or values reifying the notion of hunter-gatherer group territory.

More generally, the hierarchical spatial, temporal, and social structures of embodied routines in group contexts will never follow a strictly nested pattern. In fact, on the level of daily routine, even when logistical mobility practices are uncommon, foraging trips might result in an overnight stay. Sometimes, individuals or groups won’t even go out to search for food, reversing the spatial, temporal and social associations of food search/acquisition trips versus staying in the residential camp. So instead, non-nested hierarchical spatial, temporal, and social structures of behavioral routines are statistical patterns in populations or individual life-history patterns that develop over time. Along with cultural representations of such hierarchical structure, the complex asymmetric relational structure of routines and their multi-dimensional rhythms are part of the niche that co-evolved with our cognitive, emotional, and communication adaptations. I would go so far as to suggest that we probably cannot sufficiently explain the niche-adaptation co-evolutionary dynamic involved in our ancestors evolved linguistic capacities–constituted by our ability to conceive, understand, and construct grammatical utterances, longer narratives, and complex, imaginative and evocative metaphors–if we don’t consider the complex non-nested hierarchical structures of humans in space, time, and social configuration.


Chapais, B. (2013). Monogamy, strongly bonded groups, and the evolution of human social structure. Evolutionary Anthropology: Issues, News, and Reviews, 22(2), 52–65.

Pinker, S. (2010). Colloquium Paper: The cognitive niche: Coevolution of intelligence, sociality, and language. Proceedings of the National Academy of Sciences, 107(Supplement_2), 8993–8999.

Tooby, J. & DeVore, I. (1987). The reconstruction of hominid behavioral evolution through strategic modelling. In: (W.G. Kinzey, ed.) The Evolution of Human Behavior: Primate Models, pp. 183–227. New York: SUNY Press.

Whiten, A., & Erdal, D. (2012). The human socio-cognitive niche and its evolutionary origins. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 367(1599), 2119–2129.

Winterhalder, B. (1986). Diet choice, risk, and food sharing in a stochastic environment. Journal of Anthropological Archaeology, 5(4), 369–392.