Commentary on Humans: The Species That Changed Earth
The thought-provoking paper by Erle Ellis on “Humans – the Species that Changed Earth” explores narratives on human evolution and the proposed new geological epoch known as the anthropocene, with a view to bringing them together into a single encompassing narrative (see also Ellis 2015 1).
One of the characteristics of current debate on the anthropocene is an overriding emphasis on human impacts. The power of human action in shaping the world is highlighted, perhaps at the expense of other intermeshed forces and agencies at work. Arrows of influence all seem to point in one direction, from humans to the environment.
In much evolutionary theory, by way of contrast, the opposite is the case. As Ellis puts it, organisms are understood to adapt to environments that they cannot alter back. In standard models, evolution tends to be regarded as a one-way street.
Both these narratives are unsymmetrical, albeit in opposite ways, and need rebalancing. In this regard the logic of niche construction theory 2, 3, 4 that Ellis advocates is compelling. Organisms alter environments they are adapted to, and those alterations form part of an ecological inheritance for subsequent generations, giving rise to further adaptation. Environments both shape and are partially shaped by organisms, in a kind of double-feedback system that develops through time.
A variant of niche construction theory could also transform understanding of processes at work in the shorter time-scales of the anthropocene (where discussion is complicated by the fact that human ecological niches have cultural, technological and politico-economic dimensions). Let us take humanly-modified rivers as an example of an ecological niche. Evidence from the archaeology of rivers 5 indicates that humans rarely shape rivers in straightforward one-way applications of agency or design. On the contrary, material interventions in river flow such as the building of dams or levees usually lead to unforeseen river responses, requiring further human interventions, which in turn lead on to further river responses, and so on. It might be asked: do humans shape rivers, or do rivers shape humans?
Clearly the answer is both. For an historical instance of this, see McPhee’s account of human-river interactions in his book Control of Nature 6 – and note in passing the double-meaning in the title. A seemingly innocuous cut-off channel dug to shorten a bend in the Mississippi brought about a series of knock-on effects and responses which resulted in river flow being progressively drawn into the Atchafalaya River. River control structures were built to prevent this, which in turn led to more river responses, which had to be counteracted by the building of further control structures. Such are the social, political and economic consequences of a shift in river course and change in location of river delta that considerable financial investment is being put into maintaining current flow regimes. In building ever more complex sets of river control structures to try to keep the Mississippi in its present course, the US army Corps of Engineers is responding to river forces as well as shaping them. Arrows of influence might be better envisaged as feedback loops. People and the material flows of the river are intermeshed in accelerating processes of change.
Similar accounts of human-river interactions, albeit not always on such a large scale, could be drawn from rivers throughout the world. Even the meandering forms of apparently natural streams may result from complex processes of human intervention and river response, with buried artificial structures such as mill dams having played a major part together with geomorphological forces in accumulation of floodplain sediments and channel formation 7. A recent paper by Williams et al 8 suggests that human biosphere engineering has propelled rivers into a state shift that amounts to a third evolutionary stage of rivers. But of course rivers (neither wholly natural nor artificial, but hybrid mixtures of both) radically influence humans too – their settlement patterns, social structure and technological development. Material evidence for human-river interaction goes back far into prehistory, as evidenced by recent work on the Yellow River in China 9. It might be argued that the respective trajectories of development for both humans and river are so intertwined they should be studied together. Niche construction theory will help us do this.
Ellis asks: “why did behaviorally modern humans gain the unprecedented capacity to change an entire planet?” In trying to answer the question, I find myself disagreeing with its terms. By placing such emphasis on the power of human agency to shape the world, it risks taking us back to the ‘one-way street’ thinking for which niche construction theory is an antidote.
Ecological niches shaped by human action act back in multiple ways, presenting challenges which necessitate new or revised cultural strategies and technological solutions, binding humans and non-humans alike into the kind of double feedback loops already discussed. The implications of this are profound. It is not humans as a distinct species – set apart from other species and from the wider environment – that have gained capacity to transform worlds. It is more the case that humans – through construction of niches and the restructuring capability of these, acting back and influencing in turn – have become part of dynamic assemblages of beings, things and forces with greater power to influence Earth systems than humans alone.
Ellis himself hints at this when he describes how agricultural societies have developed ecosystem engineering regimes “from domesticated species, tillage, and irrigation to manuring and the marketplace”. agriculture has become a global set of forces capable of influencing Earth systems precisely because it consists of mixtures of people, machines, animals, plant crops, land, fossil fuels, water, irrigation ditches, fertilizers, commodity markets, local and regional economies, and so on.
Domesticated animals and plants are important parts of agricultural niches. So too are terraformed landscapes of terraced hills, rice-paddies, ploughed fields, grazed land, grain silos, chicken factories. Archaeological strata must be included too, for anthromes have depth as well as surface extent, and earthworks such as terraces, lynchets and irrigation or drainage ditches leave substantial traces in stratigraphy. Then there is the political landscape. Social inequalities and exploitation (by groups of people over other groups, or by humans over other species) also have power to impose, to shape and influence lives, and to reproduce unequal structures through time. All these are constituents of an ecological inheritance that actively shapes (as well as being shaped by) successive generations of people, impacting at the same time on the habitats of numerous other species.
The mapping of anthropogenic biomes or anthromes 10 is crucial for the way it integrates humans into global ecology, but the logic of niche construction theory applies here as much as anywhere else. Understood as dynamic and developing meshworks of unfolding relations (between humans, plant and animal species, soils, hydrologies, etc), with shaping forces working in more than one direction, anthromes could change how we think as well as how we map. If on the other hand they are conceived merely as one-directional anthropogenic impacts on the biosphere, anthromes lose much of their intellectual potential.
Recasting existing notions of the anthropocene (with its emphasis on the overwhelming power of human agency) in terms of dynamic assemblages or collectives (in which human agency has a prominent but not entirely distinct or absolute role) might lead to further understanding of human-environment interactions and processes at work in the proposed new geological epoch.
- Ellis, E. C. 2015. Ecology in an Anthropogenic Biosphere. Ecological Monographs 85:287–331.
- Laland, K. N., J. Odling-Smee, and M. W. Feldman. 2000. Niche construction, biological evolution, and cultural change. Behavioral and Brain Sciences 23:131-146.
- Laland, K. N., and M. J. O’Brien. 2010. Niche construction theory and archaeology. Journal of archaeological Method and Theory17:303-322.
- Kendal, J.R., J.J.Tehrani and J. Odling-Smee. 2011. Human niche construction in interdisciplinary focus. Philosophical Transactions of the Royal Society B. 366:1566, 785-792.
- Edgeworth, M. 2011. Fluid Pasts: archaeology of Flow. London, Bloomsbury academic.
- McPhee, J. 1989. The Control of Nature. New York: Farrar, Straus & Giroux.
- Walter, R.C. and D.J. Merritts. 2008. Natural Streams and the Legacy of Water-Powered Mills. Science 39:299-304.
- Williams, M., J. Zalasiewicz., N.Davies., I.Mazzini., J.P Goiran and S. Kane. 2015. Humans as the third evolutionary stage of biosphere engineering of rivers. Anthropocene 7, 47-53.
- Zhuang, Y. and T.R. Kidder. 2014. Archaeology of the Anthropocene in the Yellow River region, China, 8000-2000 cal. BP. Holocene 24:11, 1602-1623.
- Ellis, E. C., and N. Ramankutty. 2008. Putting people in the map: anthropogenic biomes of the world. Frontiers in Ecology and the Environment 6:439-447.