“Leave enough for everyone.” That’s what my mother used to tell us at dinner. However, the holiday season reminds me that human nature is far from innately moderate in consumption. With Black Friday as a kickoff, consumers will spend more than $600 billion by Christmas in the United States alone. As I witness droves of shoppers running through malls and stores, I wonder if their desire is driven by some insatiable appetite for their favorite products or something more fundamental about human nature.

When access is easy and supply appears unbounded, are we apt to consume without restraint? Although Christmas shoppers may be seen as easy examples of our tendency to over-consume, they are hardly alone.

In an era of globalization, where products often travel thousands of miles before reaching our hands, there exists the dangerous perception that supplies are limitless. There’s a disconnect too between our consumption choices and how their production and processing impacts the environment. All too often, the result is humans falling prey to the simple idea that more is better, which is dangerous when “more” is easy to obtain.

But we cannot be lured into this logic forever. Indeed, the current generation faces the most daunting task of any in history: figuring out how to clothe, feed, and please all seven billion of us (and counting). Accomplishing this task will require looking at systems as part of a whole, and, in that respect, the population, health, and environment (PHE) community has much to offer.

Historical Perspectives: Malthusian vs. Cornucopian

The debate on how human population impacts the environment was first brought to the forefront of political, social, and scientific thought by Thomas Malthus in 1798 following the publication of his essay, Principle of Population.

Malthus is most often remembered for his idea that human population would soon exceed agricultural production due to the exponential growth of the former compared to linear growth of the latter. His prediction was mass famine, armed conflict, disease, and death. However, his essay addresses a range of other issues, including “preventive checks” to slow population growth, including marriage postponement, birth control, abstinence, and welfare reform (i.e., repealing the so-called “poor laws”). In doing so, he raised the question of whether there is an ideal human population size – implied locally and globally – and highlighted the importance of contraception as a means to achieve it.

During the 1970s, neo-Malthusians, such as Paul Ehrlich and John Holdren, continued this line of thought. They wrote passionately about the need to respond immediately to growing population size due to the disproportionately negative impact human population growth has on the environment. And, still relevant today, they extended the idea that environmental impact encompasses more than the traditional focus on biologically rich areas, but to equally vulnerable built environments, human behavioral environments, and epidemiological environments. These types of environments represent a range of urban and rural landscapes, such as sidewalks, roadways, recreational areas, schools, traffic, sanitation facilities, and industrial centers, the quality of which are directly impacted by population size.

Malthusian thinking is not without detractors. Raising awareness of several controversial social issues in his essay did not win Malthus many friends during his lifetime or after; indeed, there are still some who consistently question whether population has any impact on the environment. Prominent among these are the cornucopian views of scientists like Julian Simon and Ester Boserup, who draw on the idea that growing population size stimulates human ingenuity to create or adopt new technology and substitute resources to avert scarcity and collapse. Contrary to popular belief, Malthus did recognize the importance and potential of technology to increase production and improve resource use efficiency; however his contention was that technology develops independently of population and the “passion of the sexes” will push population size beyond the limits of technological improvements.

Regardless of one’s view on these population-environment dynamics, it is undeniable that Malthus has influenced a great number of thinkers, and his ideas have laid some fertile ground on which demographers, economists, politicians, sociologists, and geographers debate today.

Unprecedented Global Challenges

Like Malthus, Ehrlich and Holdren’s writing continues to resonate in debates today about how population and environment issues interact.

Our generation faces unprecedented challenges: imminent climate change resulting in rising temperatures, more frequent violent storms, and altered rainfall patterns; land and water scarcity; quite possibly the peak of human population (for someone born during the 1970s and 80s, they will witness the largest addition to global population in history – four to five billion people); true globalization of world markets, driving maximal consumption among both developed and many fast-developing countries; a rapid transition to urban living, with the global urban population rising to around 70 percent by 2050; and a shift in the leading causes of death worldwide from infectious diseases (1970s and 80s), to chronic diseases (now), to neurodegenerative diseases (projected for the future).

Tackling these emerging, integrated challenges from a traditional approach focused on single sectors and interests will not succeed. For example, vector-borne diseases like malaria are affected by environment (temperature, rainfall, land cover), health (access to drugs and medical care, bednet use) and population factors (urbanization, population composition, density). Focusing on just one of these areas will not provide a sustainable solution. Rather, a strong interdisciplinary approach is needed that can integrate expertise from a number of specialists to find and implement synergistic interventions.

Modern PHE Evolves

The kind of cross-sector integration needed has been the driving force behind the development of the modern PHE field. However, PHE remains a young science that is split between those who conduct interventions or advocacy, who are supported primarily by foundations (e.g., the work of NGOs who contribute to our understanding of reproductive health and conservation as seen at the 2013 International Population, Health, and Environment Conference), and those who conduct research, supported by organizations like the National Institutes of Health and National Science Foundation (e.g., studies on migration, land use, and vector-borne disease).

On the one hand, PHE intervention programs do a laudable job meeting local demand for family planning in vulnerable environments, improving food security, and encouraging environmentally sustainable livelihoods. However, monitoring and evaluation, a strength of research organizations, is still being developed.

On the other hand, research projects do an excellent job testing relevant hypotheses, but their short time-frames often mean it’s not yet possible to scale-up potential interventions and engage communities to evaluate long-term sustainability.

Can PHE Lead the Way?

In the “age of man,” as some geologists have come to call the current epoch, PHE offers a lens already suited to examining human dynamics alongside the natural. Making sense of increasingly linked and globalized relationships will require an interdisciplinary approach to training and research, which only a handful of universities have truly embraced. The PHE community’s head-start on the challenge, including years of experience working on the complexity of measuring cross-sectoral results, gives it a chance to become much more than it is today. The future of PHE could be in addressing the biggest challenges facing mankind.

But the two sides of PHE need to come together to allow the lens to expand and take in the bigger picture. Monitoring and evaluation must continue to be a priority for programs working in the field, while research efforts identify synergies and make policy recommendations that maximize impact. Partnerships between academia, government, non-government, industry, and local communities will be needed for large-scale implementation and rapid response.

In just over a dozen years, we will likely add another billion people to the planet, almost entirely in urban environments. Cornucopians may argue this is good for some places – new intellectual capital, new ideas, etc. – but we can no longer measure the benefits obtained for one large population without considering the impact it has on another. Our global connectivity proscribes this protracted view. Interdisciplinary and cross-scale approaches need to be utilized to more thoroughly vet the interactions between human population dynamics and the environment in order to secure our future on the planet. PHE has a role to play in leading the way.