I'm in the middle of working on a paper for a special issue of Quaternary International that will bring together recent work at Olduvai Gorge and Peninj, and my contribution focuses on how (or if) carnivore avoidance played a role in conditioning where hominins chose to concentrate their activities. The overarching question, in essence, is: what it is about the areas that preserve accumulations of stones and bones at Olduvai that made them so attractive to hominins (and carnivores)? I came across a new paper by Rhonda Quinn and her colleagues (2013) that uses isotopes to reconstruct the habitat preferences of early hominins in the Turkana Basin of northern Kenya, so I thought I'd take this opportunity to think out loud about the issue of early hominin habitat preferences.
After describing the paleogeography of the Turkana Basin between about 2.4-1.4 Ma, Quinn et al. discuss how they sampled and analyzed a number of nodular pedogenic (i.e., those formed in soils) carbonates for their carbon isotope composition, which can be indicative of vegetation cover. The key part of their analysis is that they split their samples into two different groups: those not associated with artifacts (which presumably represent the sorts of habitats that were available for hominins to select) and those in close proximity to archaeological sites with lithic material (which represent the habitats that hominins actually chose). In essence, they were testing whether or not hominins selected sites with significantly different vegetation regimes relative to what was present in the region as a whole. Interestingly, the answer seems to be yes: the archaeological sites show higher levels of woody vegetation relative to the environment at large.
I'll let the authors summarize their thoughts (Quinn et al. 2013: 72-73):
The pattern they document in the Turkana Basin seems to compliment what is seen at Olduvai. Many of the archaeological occurrences in Bed I (ca. 1.9-1.8 Ma) are found in more wooded (certainly not grassland) habitats, and this appears to change once you hit upper middle Bed II times (after, say, 1.4 Ma), where sites might be located in more open habitats. This period is not covered by the Quinn et al. study, but the expectation would be that archaeological sites after 1.4 Ma in the Turkana Basin would, like those at Olduvai, start to appear in more open habitats.
We always have to be careful about sampling issues, though. I gave a talk a couple of years ago at the University of Arizona and, after mentioning that the Bed I sites all appeared to be within, or very close to, more closed, wooded habitats, while Bed II sites looked to be located in more open settings, Steve Kuhn asked a really great question: is this a real pattern or perhaps just an artifact of sampling? He was asking, in other words, whether the Bed I sites that have been analyzed to date just happen to be in these sorts of environments and the open habitat sites simply haven't yet been found (and vice verse for the Bed II sites). This is an excellent point since, it should be noted, that most of the Bed I sites cluster within a very small area of the gorge that probably does not offer an unbiased view of either Bed I landscapes or hominin behavior.
References:
Quinn, RL, Lepre, CJ, Feibel, CS, Wright, JD, Mortlock, RA, Harmand, S, Brugal, J-P, Roche, H (2013). Pedogenic carbonate stable isotopic evidence for wooded habitat preference of early Pleistocene tool makers in the Turkana Basin. Journal of Human Evolution 65, 65-78.
After describing the paleogeography of the Turkana Basin between about 2.4-1.4 Ma, Quinn et al. discuss how they sampled and analyzed a number of nodular pedogenic (i.e., those formed in soils) carbonates for their carbon isotope composition, which can be indicative of vegetation cover. The key part of their analysis is that they split their samples into two different groups: those not associated with artifacts (which presumably represent the sorts of habitats that were available for hominins to select) and those in close proximity to archaeological sites with lithic material (which represent the habitats that hominins actually chose). In essence, they were testing whether or not hominins selected sites with significantly different vegetation regimes relative to what was present in the region as a whole. Interestingly, the answer seems to be yes: the archaeological sites show higher levels of woody vegetation relative to the environment at large.
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| These graphs show the number of carbonate samples from archaeological locales (dark gray) and non-archaeological locales (white) that fall within particular vegetation types between (a) 2.4-2.2 Ma, (b) 2.0-1.8 Ma, (c) 1.8-1.6 Ma, and (d) 1.6-1.4 Ma. Note how the distributions from the archaeological localities are shifted slightly to the left (i.e., towards more wooded habitats) relative to the general environment. From Quinn et al. (2013: Figure 5). |
Our results demonstrate that lithic archaeological sites had significantly more wooded vegetation compared with what was present throughout the basin from 2.4 to 1.4 Ma. Even as environments became increasingly more grassy, lithic sites continued to be located in a more wooded landscape. Moreover, as the basin transformed from fluvial to lacustrine and back to fluvial hydrological regimes encompassing numerous microenvironments and highly variable geomorphic settings, hominin lithic sites maintained a constant pattern of fwc [= fraction woody cover] circa 40%. We suggest that our results demonstrate that tool-making hominins utilized behavioral strategies to maintain a relatively more wooded habitat through time potentially to mitigate the effects of environmental perturbations in the basin.
We interpret our results to indicate that during tool-related activities, hominins demonstrated a preference for more wooded environments in the basin than what was generally available at the time.This is a pretty interesting finding, although their time bins are, as they acknowledge, pretty broad (about 200,000 years-a lot can happen in that amount of time). It also would have been very interesting if they had considered in their analysis sites that lack lithic material but preserve butchered bones. Perhaps there is something different about those areas that encouraged hominins to butcher carcasses but take all their tools with them.
The pattern they document in the Turkana Basin seems to compliment what is seen at Olduvai. Many of the archaeological occurrences in Bed I (ca. 1.9-1.8 Ma) are found in more wooded (certainly not grassland) habitats, and this appears to change once you hit upper middle Bed II times (after, say, 1.4 Ma), where sites might be located in more open habitats. This period is not covered by the Quinn et al. study, but the expectation would be that archaeological sites after 1.4 Ma in the Turkana Basin would, like those at Olduvai, start to appear in more open habitats.
We always have to be careful about sampling issues, though. I gave a talk a couple of years ago at the University of Arizona and, after mentioning that the Bed I sites all appeared to be within, or very close to, more closed, wooded habitats, while Bed II sites looked to be located in more open settings, Steve Kuhn asked a really great question: is this a real pattern or perhaps just an artifact of sampling? He was asking, in other words, whether the Bed I sites that have been analyzed to date just happen to be in these sorts of environments and the open habitat sites simply haven't yet been found (and vice verse for the Bed II sites). This is an excellent point since, it should be noted, that most of the Bed I sites cluster within a very small area of the gorge that probably does not offer an unbiased view of either Bed I landscapes or hominin behavior.
References:
Quinn, RL, Lepre, CJ, Feibel, CS, Wright, JD, Mortlock, RA, Harmand, S, Brugal, J-P, Roche, H (2013). Pedogenic carbonate stable isotopic evidence for wooded habitat preference of early Pleistocene tool makers in the Turkana Basin. Journal of Human Evolution 65, 65-78.
