Sustainability efforts have been on the cultural radar for many years. Increasingly, cultural norms instruct us to turn off the lights when leaving a room, drive a smaller car, recycle as much as possible . . . and you too will be doing your part to save the world. In some ways, however, this day-to-day advice acts as a Band-Aid for our public conscience, at the expense of digging for deeper insights about our impending resource scarcity crisis. The effects of climate change are becoming more and more difficult to ignore, and today’s ultra-connected economic “ecosystem,” resource scarcity in one region or industry can have global implications.

Relatively little attention has been paid, however, to efforts to unearth insights into actual evolutionary and ecological principles underlying the science of how small-scale behavioral trends can interact with natural processes to produce emergent patterns at the global scale. These complexities may hinder our ability to see how even very small cultural and behavioral tendencies can either enhance or threaten our resource security—especially when considered at the scale of a human population that is 7 billion strong and growing. As the socioeconomic weave between nations, continents, and cultures becomes ever tighter, some scientists are putting a great deal of energy into investigating the relationships between large-scale ecological and evolutionary principles as they relate to resource use and misuse.

This innovative field of study, dubbed “human macroecology,” is emerging as a hothouse for new and exciting discoveries regarding the close parallels between the dynamics of human societies and natural processes. According to Joseph Burger—University of New Mexico PhD student and key player in the development of human macroecology studies—at its core, human macroecology is “the statistical study of exchanges of energy, materials and information between humans and the environment across spatial scales, from local to global and temporal scales, from years to millennia”. Macroecology considers the human species as functioning within the constraints of the natural world, rather than being uniquely divorced from natural resource limitations. This conceptual approach cuts across disciplines ranging from physics and ecology to anthropology and economics (Burnside et al. 2012), creating the opportunity for unprecedented synergy between fields. The stakes are high. “Any discussion of sustainable solutions is incomplete and will ultimately fail without this perspective,” observes Burger.

A key issue emerging from these studies is that of burgeoning population growth rates. In their 1968 book, The Population Bomb, Paul and Anne Ehrlich described the potential for severe resource shortages, societal unrest, and environmental degradation if the human population growth rate was not reduced. Their assertions garnered global attention, and were met with much uproar and condemnation from those offended by the concept of curbing human reproduction. Since the book was published, however, the number of humans on the planet has nearly doubled, and it is still on the rise. The Ehrlichs’ advice appears more and more prescient with each passing census.

The “population bomb” was a controversial concept, but not necessarily a novel one. Thomas Malthus’ insights about exponential population growth, published in 1798, had a legendary influence on Charles Darwin and his development of the theory of natural selection. The potential for interactions between the processes described by Malthus and Darwin is both fascinating and ominous. Malthus warned that populations will grow exponentially until limited by resource availability, and yet classic Darwinian adaptation—in addition to cultural innovation—allows organisms to circumvent resource limitations by increasing foraging efficiency and/or access to additional resources and decreasing mortality rates due to risks like disease and predation. If this Malthusian-Darwinian dynamic is allowed to proceed unchecked—and in step—they will interact to produce adaptations that do indeed meet immediate needs, yet may involve ultimately maladaptive behaviors (Nekola et al. 2013). For example, a population that develops an adaptation or technology to efficiently utilize a resource may end up exhausting the resource to the point that it is impossible for future generations to adapt quickly enough to sustain themselves in the depleted aftermath.

As we progressively deplete many of our natural resources, this scenario is already becoming apparent. For example, decades and decades of irrigation, diversion, and irresponsible usage rates have created a water shortage crisis across the globe, an issue currently being exemplified in the southwestern United States. The issue of drying river systems will become more urgent as climate change progresses, creating a perfect storm of both anthropogenic and climatic stress on ecological communities—including both humans and wildlife. Innovative management strategies and novel technology for taking advantage of new resources—such as the extensive irrigation systems we’ve woven across the western plains—are examples of Darwin-style adaptations that allow us to kick the Malthusian can down the road, so to speak. The question is: for how long?

This Malthusian-Darwinian dynamic (MDD) is of critical concern in the context of the world’s rapidly growing human population, and it was the topic of a recent, high-profile paper in the journal Trends in Ecology and Evolution (Nekola et al. 2013). Humans have proven to be ingenious at developing new technologies in order to acquire resources. Cultural evolution has produced a positive feedback loop between population and innovation—the more people we have, the more information we can process and use in creative new ways, and the more ways we can find to avoid short-term resource limitation. In addition, new technologies have allowed us to move past subsistence-level production, freeing individuals to focus on experimenting with even more advanced inventions and technologies.

Resources are indeed finite, however. We are living on resources borrowed from the future, and at some point our ancestors will have to pay our debts, with potentially catastrophic results. As we have already seen in the case of river systems in the United States, managing resources to maximize short-term benefits can seem innovative and useful at the time, yet at the cost of causing magnified problems in the future.

There is, of course, another point of view on these issues. The “Cornucopian” approach challenges the validity of MDD’s concerns by staunchly asserting that we are limited only by the powers of human innovation, which will inevitably prevent us from succumbing to catastrophic resource limitation. Proponents of the Cornucopian view emphasize the process of Darwinian adaptation, and assert that progressive adaptations will allow us to overcome resource limitations indefinitely (Nekola et al. 2013). Whether they are correct or not may become apparent in the near future, as we reach critical mass in our utilization of resources such as fresh water, seafood, agricultural land, and fossil fuels. This sounds dire, but from a Cornucopian perspective this critical mass of people is essential in order innovate our way around current constraints and push forward.

The views of Cornucopians and the MDD perspective are not necessarily mutually exclusive, however. Burger points out that the MDD approach actually incorporates the Cornucopian perspective by acknowledging that technological advances allow us to continue to push environmental limits. Burger cautions, however, that “the scope for major innovations required to maintain global trajectories in population and economy is reaching diminishing returns as we are now pushing against constraints at the global scale.” Only time will reveal the outcome, but meanwhile, human macroecology research will keep us as informed as possible as to evolutionary and ecological dynamics of the processes at hand.

The insights obtained by applying ecology to human socioeconomics are fascinating and sometimes disturbing. Researchers have discovered striking parallels between the energy requirements of human economies and biological metabolism (Brown et al. 2011), economic implications for the laws of thermodynamics (Burnside et al. 2012; Burger et al. 2012), and implications of the fundamental interactions between resource limitations and Darwinian innovation/cultural evolution (Nekola et al. 2013). The trends that this research continually unveils—massive overexploitation of resources at an unsustainable rate—are very serious.

For example, Burger notes that macroecology research indicates that in order for the global human population to stabilize (achieving zero population growth; ZPG), the entire world must match the per capita energy consumption of the most developed countries. Imagine, everyone in Africa, Asia, India, Brazil, and so on blasting through resources at the rate of an average American before our population could finally stabilize. There is just not enough energy available to support a population of 7 billion—let alone 10 billion—with standards of living comparable to the United States.

Furthermore, Burger notes that macroecology research has demonstrated that “UN predictions on population growth are much too optimistic,” meaning that progressive resource depletion “provides formidable challenges to achieving ZPG in the absence of strict government regulated population control.” In other words, we don’t have the resources available to reach ZPG through the natural relationship between energy consumption and population growth, meaning that an acute energy scarcity crisis will occur long before we manage to stop adding more and more humans to the global tally each year.

The concept of human macroecology has yet to attain broad public awareness or appreciation, yet the issues at hand cannot be addressed without cohesive efforts involving two forms of intellectual integration: building bridges across scientific disciplines as well as between scientists and policy makers. Scientific figureheads such as the Ehrlichs have already shown support for the approach (Erhlich & Ehrlich 2013). Macroecological insights into the trajectory of human society, including how populations will grow and sustain themselves, will become of increasing importance as populations continue to burgeon and climate trends continue to shift. It is becoming increasingly apparent that the health and well-being of both civilization and nature are inextricably linked.

These issues are highly relevant to the livelihoods of scientists and non-scientists alike, and the field of macroecology stands on the forefront of research into critically important issues with broad implications for the environment, human health, and political stability. Action is needed by both scientists and society in order to find solutions that will allow our species to persist and thrive while minimizing further environmental damage.

Cited Sources:

Brown, J. H., W. R. Burnside, A. D. Davidson, J. P. DeLong, W. C. Dunn, M. J. Hamilton, et al. 2011. Energetic limits to economic growth. BioScience 61:19–26.

Burger, J. R., C. D. Allen, J. H. Brown, W. R. Burnside, A. D. Davidson, T. S. Fristoe, et al. 2012. The Macroecology of sustainability. PLOS Biology 10:e1001345.

Burnside, W. R., J. H. Brown, O. Burger, M. J. Hamilton, M. Moses and L. M. A. Bettencourt. 2012. Human macroecology: linking pattern and process in big-picture human ecology. Biological Reviews 87:194–208.

Daly, H. E. 2005. Economics in a full world. Scientific American 293:100–107.

Ehrlich, P. R. and A. H. Ehrlich. 2013. Can a collapse of global civilization be avoided? Proceedings of the Royal Society B 280:20122845.

Mace, G. M. 2012. The limits to sustainability science: ecological constraints or endless innovation? PLOS Biology 10:e1001343.

Matthews, J. H. and F. Boltz. 2012. The shifting boundaires of sustainability science: Are we doomed yet? PLOS Biology 10:e1001344.

Nekola, J. C., C. D. Allen, J. H. Brown, J. R. Burger, A. D. Davidson, T. S. Fristoe, et al. 2013. The Malthusian-Darwinian dynamic and the trajectory of civilization. Trends in Ecology & Evolution 1643.

Images: Population curve from census.gov; Tokyo by LuxTonnerre