Human populations grow until they overshoot their carrying capacity and collapse. Game over. Thank you Malthus! (1798; and Ehrlich 1968).
Not so fast! There’s something wrong with this story: it almost never happens. Human populations do collapse – but not because of population growth itself; collapses are most commonly related to disease, climate change or societal failures (eg. Zhang et al. 2011). Generally, human populations continue to grow, lifting their environmental carrying capacity as they go.\
I first encountered this reality when studying long-term ecological changes in the ancient villages of China’s Tai Lake Region (Ellis and Wang 1997; Ellis et al. 2000). Long-sustained population growth in this densely populated region went against all of my biological training- surely every population must have a carrying capacity! (“Ehrlich’s error”). But the data were clear: populations increased for millennia and so did the local food supply. Though populations did collapse in the 1800s, this was caused by the Taiping rebellion- not food supply.
I was fresh out of theory. Enter Ester Boserup, with her theory of agricultural intensification (Boserup 1965). Hers’ is still the most general theory explaining how human populations can continue to grow despite apparent environmental limits. According to Boserup, as human populations increase, they adopt more productive technologies (eg. agriculture and other systems of ecosystem engineering), increasing the carrying capacity of human environments as needed. This is not a techno-utopian argument. Boserup does not imply that new technologies make life better, or that technologies are developed because they are needed- she merely posits that when people need to sustain themselves, they will do whatever it takes- even if this means using more labor or other resources.
Boserup’s theory of intensification has been challenged over the years but has stood firm as the core theory of agricultural land use (Turner II 2010, Stone 2001). Better still, Boseruppian theory is alive and well- witness the recent (and wonderful!) Ester Boserup Centennial Tribute Conference; and is still inspiring. Her theory has been expanded to include all sorts of complexities (Boserup 2.0), including periods of increasing population with only minimal increases in productivity (“agricultural involution”; Geertz 1963) and even “Malthusian” phases, when populations briefly “overshoot”- though usually agricultural systems change dramatically long before this happens (“regime shifts”). The figure at right puts these theories in their most general form: the theory that human systems adapt to and evolve around environmental obstacles (Figure inspired by Billie Turner II’s presentation at the Boserup conference; used in my AGU 2010 poster).
Boserupian intensification has helped explain land clearing even in the deep past (Ruddiman and Ellis 2009). At present, as human populations are growing and urbanizing, agricultural demand has increased so much that the most intensive agricultural systems are becoming dominant. The good news is that the most intensive systems tend to focus on the most productive land – marginal lands are increasingly abandoned and left to regenerate ( the “forest transition”; eg. Rudel et al. 2009). So even as we go off the end of Boserup’s chart, disaster is not the result and intensification continues- though the planet will never be the same- our agriculture has now transformed the planet for the long-term (Ellis et al. 2010).
So far, Boserup has been right and Malthus and Ehrlich have been wrong. And I would bet that the future will also be Boseruppian (Boserup 3.0). We humans will be around for the long term, adapting the earth to us, and then adapting to the earth we create. However, just like the paleolithic humans who once hunted and gathered on the land where you now sit reading this, we will never be able to imagine the Anthropocene world our progeny will create. But maybe Boserup could have.
(1910 – 1999)
Ester Boserup Centennial Tribute Conference
Ester Boserup (Wikipedia)
Thomas Robert Malthus
(1766 – 1834)
Thomas Robert Malthus
See more about Human populations: Great new feature at National Geographic: Population 7 Billion
Boserup, E. 1965. The Conditions of Agricultural Growth: The Economics of Agrarian Change under Population Pressure. London: Allen & Unwin
Boserup, E. 1976. Environment, Population, and Technology in Primitive Societies. Population and Development Review, 2, 21-36.
Boserup, E. 1981. Population and Technological Change: A Study of Long Term Trends. Chicago: University of Chicago Press
Ehrlich, P. 1968. The Population Bomb. Ballantine Books, New York.
Ellis, E. C. & Wang, S. M. 1997. Sustainable traditional agriculture in the Tai Lake Region of China. Agriculture, Ecosystems & Environment, 61, 177-193. <download>
Ellis, E. C., Li, R. G., Yang, L. Z. & Cheng, X. 2000. Nitrogen and the sustainable village. Agroecosystem Sustainability: Developing Practical Strategies (ed. by S.R. Gliessman), pp 95-104. CRC Press, Boca Raton, Florida. <download>
Ellis, E. C., Klein Goldewijk, K., Siebert, S., Lightman, D. & Ramankutty, N. 2010 Anthropogenic transformation of the biomes, 1700 to 2000. Global Ecology and Biogeography, 19, 589-606. <get it here>
Geertz, C. 1963. Agricultural Involution: The Process of Ecological Change in Indonesia. University of California Press, Berkeley, CA.
Malthus, T.R. 1798. An Essay on the Principle of Population, as it Affects the Future Improvement of Society, with Remarks on the Speculations of Mr Godwin, M. Condorcet, and other writers. London: J. Johnson. can be read online <here>, and <here>.
Rudel, T. K., L. Schneider, M. Uriarte, B. L. Turner, R. DeFries, D. Lawrence, J. Geoghegan, S. Hecht, A. Ickowitz, E. F. Lambin, T. Birkenholtz, S. Baptista, and R. Grau. 2009. Agricultural intensification and changes in cultivated areas, 1970-2005. Proceedings of the National Academy of Sciences 106:20675-20680.
Ruddiman, W. F. & Ellis, E. C. 2009. Effect of Per-Capita Land use Changes on Holocene Forest Clearance and CO2 Emissions. Quaternary Science Reviews, 28, 3011-3015.
Stone, G. D. 2001. Theory of the square chicken: advances in agricultural intensification theory. Asia Pacific Viewpoint 42:163-180.
Turner II, B. L. & Fischer-Kowalski, M. (2010) Ester Boserup: An interdisciplinary visionary relevant for sustainability. Proceedings of the National Academy of Sciences, 107, 21963-21965.
Zhang, D. D., Lee, H. F., Wang, C., Li, B., Zhang, J., Pei, Q. & Chen, J. 2011. Climate change and large-scale human population collapses in the pre-industrial era. Global Ecology and Biogeography, xx-xx http://dx.doi.org/10.1111/j.1466-8238.2010.00625.x.