“Climate, Environment and Early Human Innovation: Stable Isotope and Faunal Proxy Evidence from Archaeological Sites (98-59ka) in the Southern Cape, South Africa”


Roberts, P., C. S. Henshilwood, K. L. van Niekerk, P. Keene, A. Gledhill, J. Reynard, S. Badenhorst and J. Lee-Thorp. 2016 PLoS One 11(7):e0157408.


The Middle Stone Age (MSA) of southern Africa, and in particular its Still Bay and Howiesons Poort lithic traditions, represents a period of dramatic subsistence, cultural, and technological innovation by our species, Homo sapiens. Climate change has frequently been postulated as a primary driver of the appearance of these innovative behaviours, with researchers invoking either climate instability as a reason for the development of buffering mechanisms, or environmentally stable refugia as providing a stable setting for experimentation. Testing these alternative models has proved intractable, however, as existing regional palaeoclimatic and palaeoenvironmental records remain spatially, stratigraphically, and chronologically disconnected from the archaeological record. Here we report high-resolution records of environmental shifts based on stable carbon and oxygen isotopes in ostrich eggshell (OES) fragments, faunal remains, and shellfish assemblages excavated from two key MSA archaeological sequences, Blombos Cave and Klipdrift Shelter. We compare these records with archaeological material remains in the same strata. The results from both sites, spanning the periods 98–73 ka and 72–59 ka, respectively, show significant changes in vegetation, aridity, rainfall seasonality, and sea temperature in the vicinity of the sites during periods of human occupation. While these changes clearly influenced human subsistence strategies, we find that the remarkable cultural and technological innovations seen in the sites cannot be linked directly to climate shifts. Our results demonstrate the need for scale-appropriate, on-site testing of behavioural-environmental links, rather than broader, regional comparisons.

We live in interesting times.  I hope you will forgive me for a somewhat disjointed post. A month or so ago I was scheduled to fill this blog slot with either a reading post or opinion piece relating to the Anthropocene.  I decided to write on one of several recent studies that challenge common assumptions about the origins of human social behavior, with implications for how we see ourselves today. If you are familiar with my other posts, I am fond of critiquing adventures in what Clive Gamble calls Originsland, a deep past where we attempt to isolate prime movers for change, or locate seemingly innate human behaviors such as environmental degradation, symbolic expression, or interpersonal violence. Originsland is important for generating and testing hypotheses about what it means to be human, and what the human niche may be. One trouble is that in working with a fragmentary record of human practice 10,000 or 100,000 years ago, we often reveal as much about our current concerns than the actual processes of becoming modern.

In the spirit of the arrow of social change, the article I chose to present is focused on a substantive question of human origins: where does innovation and creativity arise from? A common argument is that early humans in southern Africa, those who we often refer to as “behaviorally modern,” adapted new social and technological strategies as a consequence of climatic forcing that required solutions to subsistence or demographic crises (see previous posts regarding the work of Kim Sterelny).  Lacking detailed histories, it has been easier to default to large scale forcing variables for explanation. Such innovations are evidenced by new apparently symbolic practices such as the use of red ochre and alternative technological styles.  In this article, Roberts and colleagues test whether these emergences of behaviorally modern human practice can be explained by climate forcing. They developed a high-resolution climatic and subsistence reconstruction from two key sites, Blombos Cave and Klipdrift Shelter, which span roughly 98,000 to 59,000 years ago.

Roberts et al. failed to find concordance between these new practices and climate alterations. While they conclude that there was climate change, and that humans responded with subsistence regime shifts, it was neither severe nor apparently extensive enough to warrant immediate innovations. The authors posit several social alternatives to the climate forcing model, including increasing long-distance exchange, or perhaps population movement and inter-cultural negotiations. As they write, “although our species has shown itself to be highly resilient in the face of climatic and environmental instability it is clearly not wholly dependent on such changes for its innovation” (p. 16). This is a potentially powerful insight: what humans as a species would become is based on our social relations. At the scale of (probably) low-density populations at any rate, our innovations were likely a product of social cooperation, perhaps to negotiate an existential threat (which does not necessarily exclude the “natural” world).

Even though the ancient is still very much with us in the form of our genes, our landscapes, our institutions, and perhaps even our beliefs, this week the gulf between the ancient and contemporary feels, to me at least, vast. When agreeing to write a post for this week, I don’t remember at the time linking it with the election. Now I am writing this for publication one week after a U.S. presidential election that has many implications for climate policy, environmental change, and social justice (just to name a few) in the coming years and perhaps for many generations. As an archaeologist, I have been trained to think in different temporal and spatial scales. Many of us were instructed early on that social change occurred slowly, glacially even, perhaps with the occasional rapid transformation. No doubt, many biologists and geologists learned the same. This perspective was in part the product of how the archaeological record forms and is preserved, making the isolation of individual events problematic at best. Recent advances in our temporal precision, such as the use of Bayesian statistics to model radiocarbon assays, have shown that rapid change is not rare at all. Lynn Soreghan has discussed similar revelations in geology. It is not that we should always expect rapid change, but that we should recognize that rapid change is a real possibility. In that sense, this has been a confusing week for many folks, no doubt due in part to the dissonance between a present and imagined future prior to the election and a future (now) that at least a quarter of the U.S. population was not expecting. I suspect many are experiencing one mode of future dysphoria or another.

In my own travels in Originsland, I find the insights of Roberts and colleagues valuable, particularly now. Detailed histories allow us to understand the interrelation of past processes, but also to more fully appreciate the complexities of human responses in the face of social change.  As we experience change (assuming we recognize it as such), no matter the source, it is in the context of our social environment that we negotiate, create, and innovate.

Clive Gamble 2007. Origins and Revolutions: Human Identity in Earliest Prehistory. Cambridge: Cambridge University Press. Gamble presents the idea of “originsland,” an imagined past that reveals essential human characteristics.

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