Ostrich eggshell bead strontium isotopes reveal persistent macroscale social networking across late Quaternary southern Africa Brian A. Stewarta,b,1, Yuchao Zhaoa, Peter J. Mitchellc,d, Genevieve Dewarb,e, James D. Gleasonf, and Joel D. Blumf aDepartment of Anthropology and Museum of Anthropological Archaeology, University of Michigan, Ann Arbor, MI 48109-1259; bRock Art Research Institute, University of the Witwatersrand, 2050 Wits, South Africa; cSchool of Archaeology, University of Oxford, OX1 3TG Oxford, United Kingdom; dSchool of Geography, Archaeology, and Environmental Studies, University of the Witwatersrand, 2050 Wits, South Africa; eDepartment of Anthropology, University of Toronto Scarborough, Scarborough, ON M1C 1A4, Canada; and fEarth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109-1005 Edited by T. Douglas Price, University of Wisconsin–Madison, Middleton, WI, and approved January 31, 2020 (received for review December 3, 2019) Hunter-gatherer exchange networks dampen subsistence and possibilities when resources in their own territory become scarce reproductive risks by building relationships of mutual support (15). Indebtedness runs between but also—via affinal kin—beyond outside local groups that are underwritten by symbolic gift individual partnerships, enveloping participants in broader net- exchange. Hxaro, the system of delayed reciprocity between works of mutual reliance. Risks are minimized by strategically Ju/’hoãn individuals in southern Africa’s Kalahari Desert, is the best- selecting partners at diverse distances to meet diverse exigencies, known such example and the basis for most analogies and models of from daily subsistence fluctuations (coresident and neighboring hunter-gatherer exchange in prehistory. However, its antiquity, driv- kin) to regional resource failures (distant relatives living far away). ers, and development remain unclear, as they do for long-distance Although the former are more common, nonlocal partnerships are exchanges among African foragers more broadly. Here we show considered essential. Wiessner found that nearly a third of an through strontium isotope analyses of ostrich eggshell beads from average Ju/’hoãn’s hxaro partners live over 50 km away, and nearly highland Lesotho, and associated strontium isoscape development, all families in her sample had at least one based 150- to 200-km that such practices stretch back into the late Middle Stone Age. We distant (14). These multiscalar networks of reciprocity enmesh ANTHROPOLOGY argue that these exchange items originated beyond the macroband Ju/’hoãn communities in support systems spanning many thousands from groups occupying the more water-stressed subcontinental inte- of square kilometers that are simultaneously a superbly resilient rior. Tracking the emergence and persistence of macroscale, transbiome adaptation to the ecological vagaries of desert life (15), a means of social networks helps illuminate the evolution of social strategies securing access to potential marriage partners (21), and a mechanism needed to thrive in stochastic environments, strategies that in our case study show persistence over more than 33,000 y. for reinforcing egalitarian social values (22). The most ubiquitous, highly valued, and traditionally impor- hxaro ostrich eggshell beads | strontium isotope analysis | social networks | tant gifts are those adorned or strung with ostrich eggshell late Quaternary | southern Africa beads, and so intimately are the two associated that the same word (//ri) denotes both beadwork and hxaro gifts in general (15). In the Kalahari, ostrich eggshell beads are particularly funda- xchanges of material culture characterize all living societies mental to girls’ initiation ceremonies and marriage exchanges, E(1). Their pervasiveness positions them at the core of the human experience and anthropological inquiry (2, 3). Among small-scale societies, material exchanges typically take the form Significance of mutual gift-giving. While extraordinarily diverse with respect to specific traditions, the value of such transactions lies less with Hunter-gatherers like the Ju/’hoãnsi (!Kung) San use exchange the goods exchanged than with the underlying social relations networks to dampen subsistence and reproductive risks, but al- they symbolize (4, 5). Reciprocal transfers are particularly vital most nothing is known of how, when, and why such practices among hunter-gatherers, kindling and cementing bonds within and emerged. Strontium isotope analysis of one preferred San ex- between communities. The exchange of portable, symbol-laden change item, ostrich eggshell beads, from highland Lesotho shows ∼ objects like beads is widely thought to represent a major thresh- that since the late Middle Stone Age 33 ka, such networks old in human behavioral evolution (6–8), a “release from prox- connected ecologically complementary regions over minimal dis- tances of several hundred kilometers. Rapidly changing environ- imity” that massively expanded the spatial and temporal scope of mental conditions during Marine Isotope Stage 3 (∼59 to 25 ka) human interaction and information transmission (9). The social likely placed a premium on developing effective means of miti- relations and networks such transfers underwrite serve both as gating subsistence and demographic risks, with ostrich eggshell conduits for socioecological information and as assurances of ac- — beads providing a uniform medium of personal decoration and cess to resources (10). Exchange is thus one of numerous strategies exchange highly suitable for binding together extended open including mobility, division of labor, food sharing, storage, and tra- social networks. ditions of oral and visual art—that hunter-gatherers enact to dampen subsistence and demographic risks (11, 12). Author contributions: B.A.S. designed research; B.A.S., Y.Z., J.D.G., and J.D.B. performed The best-known example of hunter-gatherer exchange is hxaro, research; B.A.S. and G.D. collected samples; B.A.S., Y.Z., P.J.M., G.D., J.D.G., and J.D.B. the system of delayed, balanced reciprocity practiced by the analyzed data; and B.A.S., Y.Z., P.J.M., G.D., J.D.G., and J.D.B. wrote the paper. Ju/’hoãnsi of southern Africa’s Kalahari Desert. Prominent thanks The authors declare no competing interest. to the work of Wiessner (13–17), hxaro is one of many analogous This article is a PNAS Direct Submission. traditions observed among San cultures (18–20). Hxaro rela- Published under the PNAS license. tionships are mutual gift-giving partnerships between two 1To whom correspondence may be addressed. Email: [email protected]. members of the same or different bands. Hxaro fulfills several This article contains supporting information online at https://www.pnas.org/lookup/suppl/ key societal functions, but primarily provides Ju/’hoãn individuals doi:10.1073/pnas.1921037117/-/DCSupplemental. and families with alternative residences and associated foraging www.pnas.org/cgi/doi/10.1073/pnas.1921037117 PNAS Latest Articles | 1of10 Downloaded by guest on October 2, 2021 with the most lavish beadwork items employed for the latter and archaeological ostrich eggshell beads spanning the past ∼33 ka in advertising the status and connections of families (23). Al- from the Maloti-Drakensberg Mountains of highland Lesotho though not as ancient as marine shell ornaments, ostrich eggshell (Fig. 1). 87Sr/86Sr ratios of ostrich eggshell beads reflect the beads have a deep African pedigree, first appearing ∼50 to 40 ka bioavailable Sr in local rocks that is transferred to vegetation and during mid-Marine Isotope Stage (MIS) 3 in archaeological con- water consumed by ostriches during the breeding season. When texts variously described as late Middle Stone Age (MSA), early 87Sr/86Sr ratios are sufficiently differentiated across the land- Later Stone Age (LSA), and transitional MSA/LSA (24–28). Like scape, they can be used to identify the predominant lithology of all objects of bodily adornment, they and later archaeological where an egg was originally laid and discovered. These bead data specimens were clearly intended for interpersonal and intergroup are presented alongside—and interpreted using—a strontium signaling (7). Beyond this obvious inference, however, we cur- isoscape that we are developing for the Karoo Supergroup, rently possess no knowledge of how they functioned in African southern Africa’s most extensive geological series, which centers hunter-gatherer societies in any period or place beyond the eth- on the Maloti-Drakensberg, a rugged, deeply incised montane nographic Kalahari. Did they form part of multiscalar exchange grassland that is the highest mountain system along southern networks that helped distribute risk as among historical and con- Africa’s Great Escarpment. This system exacerbates the steep temporary Ju/’hoãnsi? Or were their uses in earlier periods or east-west rainfall and evaporation gradients that characterize regions outside the Kalahari altogether different? How might southernmost Africa, forming a climatic interface between its these roles have changed through time, and when and in what high-rainfall coastal forelands and its drier, more seasonal in- socioecological contexts do we see the advent in Africa of mate- terior plateau (Fig. 1). It also gives rise to southernmost Africa’s rially mediated, geographically expansive social networks? The largest river, the Orange (or Senqu), which originates in highland answers to these questions concerning the antiquity, drivers, and