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Human and nature dynamics (HANDY): Modeling inequality and use of
resources in the collapse or sustainability of societies:

We would especially like to thank the editors of this journal for alerting us to the modeland work done by Brander and Taylor, of which we were unaware, and allowing us to revise our article to account for this newinformation.

This work was partially funded through NASA/GSFC grant NNX12AD03A.Double-click to edit text, or drag to move.



Methodological and Ideological Options Human and nature dynamics (HANDY): Modeling inequality and use of resources in the collapse or sustainability of societies

Safa Motesharrei a,⁎, Jorge Rivas b, Eugenia Kalnay c
a School of Public Policy and Department of Mathematics, University of Maryland; and National Socio-Environmental Synthesis Center (SESYNC)
b Department of Political Science, University of Minnesota; and Institute of Global Environment and Society (IGES)
c Department of Atmospheric and Oceanic Science and Institute of Physical Science and Technology, University of Maryland
a r t i c l e i n f o a b s t r a c t

Article history: Received 1 October 2012
Received in revised form 11 February 2014
Accepted 18 February 2014
Available online 2 April 2014
Human–nature dynamics
Societal collapse
Carrying capacity
Overshoot vs. sustainability
Economic inequality
Ecological strain

There are widespread concerns that current trends in resource-use are unsustainable, but possibilities of overshoot/collapse remain controversial. Collapses have occurred frequently in history, often followed by centuries
of economic, intellectual, and population decline. Many different natural and social phenomena have been invoked to explain specific collapses, but a general explanation remains elusive.

In this paper, we build a human population dynamics model by adding accumulated wealth and economic inequality
to a predator–prey model of humans and nature. The model structure, and simulated scenarios that
offer significant implications, are explained. Four equations describe the evolution of Elites, Commoners, Nature,
andWealth. The model shows Economic Stratification or Ecological Strain can independently lead to collapse, in
agreement with the historical record.
The measure “Carrying Capacity” is developed and its estimation is shown to be a practicalmeans for early detection
of a collapse. Mechanisms leading to two types of collapses are discussed. The new dynamics of this model
can also reproduce the irreversible collapses found in history. Collapse can be avoided, and population can reach a
steady state at maximumcarrying capacity if the rate of depletion of nature is reduced to a sustainable level and if
resources are distributed equitably.
© 2014 The Authors. Published by Elsevier B.V.
1. Introduction
There are widespread concerns that current trends in population
and resource-use are unsustainable, but the possibilities of an overshoot
and collapse remain unclear and controversial. How real is the possibility
of a societal collapse? Can complex, advanced civilizations really
collapse? It is common to portray human history as a relentless and inevitable
trend toward greater levels of social complexity, political organization,
and economic specialization, with the development of more
complex and capable technologies supporting ever-growing population,
all sustained by the mobilization of ever-increasing quantities of
material, energy, and information. Yet this is not inevitable. In fact,
cases where this seemingly near-universal, long-term trend has been
severely disrupted by a precipitous collapse – often lasting centuries –
have been quite common. A brief review of some examples of collapses
suggests that the process of rise-and-collapse is actually a recurrent
cycle found throughout history, making it important to establish a
general explanation of this process (Chase-Dunn and Hall, 1997; Goldstein,
1988; Meadows et al., 1972; Modelski, 1987; Tainter, 1988;
Turchin and Nefedov, 2009; Yoffee and Cowgill, 1988).
The Roman Empire's dramatic collapse (followed by many centuries
of population decline, economic deterioration, intellectual regression,
and the disappearance of literacy) is well known, but it was not the
first rise-and-collapse cycle in Europe. Prior to the rise of Classical
Greco-Roman civilization, both the Minoan and Mycenaean Civilizations
had each risen, reached very advanced levels of civilization, and
then collapsed virtually completely (Morris, 2006; Redman, 1999).
The history ofMesopotamia – the very cradle of civilization, agriculture,
complex society, and urban life – presents a series of rise-and-declines including
the Sumerians, the Akkadian, Assyrian, Babylonian, Achaemenid,
Seleucid, Parthian, Sassanid, Umayyad, and Abbasid Empires (Redman
et al., 2004; Yoffee, 1979). In neighboring Egypt, this cycle also appeared
repeatedly. In both Anatolia and in the Indus Valley, the very large and
long-lasting Hittite and Harrapan civilizations both collapsed so
completely that their very existencewas unknown until modern archeology
rediscovered them. Similar cycles of rise and collapse occurred repeatedly
in India, most notably with the Mauryan and the Gupta
Empires (Edwards et al., 1971, 1973; Jansen et al., 1991; Kenoyer,
1998; Thapar, 2004). Southeast Asia similarly experienced “multiple
Ecological Economics 101 (2014) 90–102
⁎ Corresponding author.
E-mail addresses: ssm@umd.edu (S. Motesharrei), jorgerodrigorivas@gmail.com
(J. Rivas), ekalnay@atmos.umd.edu (E. Kalnay).
0921-8009 © 2014 The Authors. Published by Elsevier B.V.
Contents lists available at ScienceDirect
Ecological Economics
journal homepage: www.elsevier.com/locate/ecolecon
Open access under CC BY license.
Open access under CC BY license.