Custodians of deep time?

Over break, I was finally able to catch up on some of the reading that had piled up on my desk. An interesting short paper was an opinion piece by Douglas Erwin (2009) entitled "A call to the custodians of deep time". In a nutshell, he makes the case for paleontologists to move away from describing and cataloging extinct species and to begin thinking about how to understand how the diversity in fossils can be integrated into broader discussions about animal biodiversity against the background of geological time. Erwin (2009:282) argues that "paleontologists are the custodians of the only record of ecosystem undamaged by human activities," hence the critical importance of understanding what fossils say about biodiversity prior to the ravages wrought by humanity.

While I agree that it's important to make every effort to relate the results of 'paleo' disciplines to ones grounded in observations of extant biological and ecological communities, I was a bit puzzled by his selection of 10,000BP as the date from which humans have been 'destroying' the Earth. It is clear that the ecological legacies of human actions have much greater time depth, as indicated in this post of a few years ago, where Neanderthals appear to have overhunted certain large mammals near Kebara Cave, Israel. In fact, much recent research on the millennia preceding the development of agriculture (e.g., Stiner and Kuhn 2006) has shown that growing human population densities appears to have been a significant stressor on all sorts of animal communities, from aurochs to limpets. This has led some researchers to dub humans as "the ultimate ecological engineers" (Smith 2007), and to highlight that human impacts on their environment stretch back considerably further than 10,000BP. Granted, human impacts on their environments are certainly more conspicuous after the adoption of agriculture, in part due to the concomitant adoption of a sedentary lifeway and to the clearing of land required by this new subsistence strategy. But that doesn't mean our ancestors weren't affecting the make-up of plant and animal communities earlier. Indeed, a good case can also be made that they were also impacting their landscapes in significant ways: ever thought about how many thousands of tons of stone have been flaked since the first stone tools were made over 2.5 million years ago? I was speaking to a colleague not too long ago who told me that the residues of one of his lithic experiments weighed over 100kg. How much stone might have people knapped in the past, when their life could, quite literally, depend on it?

In any case, the point here is that zeroing in on humans as a destructive force raises more problems than it solves, in my opinion... really, how far back should we push this? To the first modern humans? To the first Neanderthals? The first erectines? Australopithecines? What?

Fundamentally, though, Erwin's basic point is a good one: It is imperative to be able to cast the conclusions of scientific research based on extant and historical observations to prehistoric ('paleo') ones. This is to be able to relate the world we know and experience to the rest of the history of life, which is essential for an coherent evolutionary perspective to develop and to integrate evolutionary change at different timescales. This point is also the gist of a short follow-up opinion piece about Erwin's paper by Louys et al. (2009) who argue that

"The worlds of palaeoecologists and ecologists are very much apart, and dialogue between the two remains muted...

The way modern and fossil ecosystems are described will necessarily be different, but researchers should strive to see whether the rules described for modern ecosystems hold over geological time. After all, the fossil record provides the only way to study changes in ecosystems over more than centennial timescales, along with samples of non-analogous ('extinct') ecosystems and habitats." (Louys et al. 2009:847).

In a way, I feel that paleoanthropologists really are at the forefront of such efforts. Sure, there is still much effort being devoted to whether or not a given fossil represents a distinct species from broadly coeval ones or to whether or not higher bladelet proportions in an archaeological assemblage indicates a distinct technocomplex. After all, we need to have some playing pieces to explore the what Erwin (2009) likens to a 'chessboard' of ecological niches documented across the world. But increasingly, paleoanthropologists are explicitly trying to account for variability (both biological and behavioral) and placing it in ecological context. Furthermore, making inferences about past hunter-gatherer behavioral systems by drawing on both ethological and ethnographic observations made on extant communities can be highly informative, if undertaken with due caution (Wobst 1978). In fact, this is the topic of a recent volume (Papagianni et al. 2008), which I recently reviewed in PaleoAnthropology (freely accessible at the link) and which tackles the issue of integrating observations about extant and extinct forager groups at various scales. Obviously, the time scales involved may be somewhat disparate, and I don't know for certain whether the situation is truly as dismal as suggested by Erwin (2009) and Louys et al. (2009). But, on that level at least, paleoanthropology can be considered a good disciplinary example in terms of strategies for ecologists and paleoecologists and biologists and paleontologists to implement to profitably integrate their observations.

References

Erwin, D. 2009. A call to the custodians of deep time. Nature 462:282-283.

Louys, J., L.C. Bishop, and D.M. Wilkinson. 2009. Opening dialogue between the recent and long ago. Nature 462:847.

Papagianni, D., R. Layton, and H. Maschner (eds.). 2008. Time and Change. Archaeological and Anthropological Perspectives on the Long-Term in Hunter-Gatherer Studies. Oxbow Books, Oxford.

Smith, B.D. 2007. The ultimate ecosystem engineers. Science 315:1797 - 1798.

Stiner, M.C., and S.L. Kuhn. 2006. Changes in the 'connectedness' and resilience of Paleolithic societies in Mediterranean ecosystems. Human Ecology 34:693-712.

Wobst, H.M. 1978. The archaeo-ethnology of hunter-gatherers or the tyranny of the ethnographic record in archaeology. American Antiquity 43:303-309.