Human Carrying Capacity – Fanciful Fiction or Deadly Reality

One of the first courses I took in college toward my degree in wildlife management was a population dynamics class.  And one of the first readings was the classic story of the boom-bust population cycles of the moose and wolf of Isle Royale Michigan, where, prior to the wolf as a keystone predator, the island’s moose herd would overpopulate and overgraze, resulting in starvation and mass die-offs.  When the wolves were eventually introduced the belief was that the keystone predator would help stabilize the moose population.  But the history of Isle Royale moose and wolf populations has been wildly unpredictable, affected not only by availability of food, but by disease, tick outbreaks, severe winters, and immigrant wolves.  Every five years has brought unpredictable fluctuations in both populations, and every five years has been different from all other five-year periods.  Even in the 1980s when my classmates and I were closely following this study, it was believed that the populations would reach equilibrium.  But that never happened.

Although such predator-prey studies help to explain the causal elements of carrying capacity for animals, the concept of human carrying capacity has always been elusive and is far more complicated.  Since the days of Malthus, such dire predictions of human population catastrophe have haunted the minds of many.  In 1798, Malthus wrote,

The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race. The vices of mankind are active and able ministers of depopulation. They are the precursors in the great army of destruction, and often finish the dreadful work themselves. But should they fail in this war of extermination, sickly seasons, epidemics, pestilence, and plague advance in terrific array, and sweep off their thousands and tens of thousands. Should success be still incomplete, gigantic inevitable famine stalks in the rear, and with one mighty blow levels the population with the food of the world.
—Malthus T.R. 1798.
I’ve always had an academic interest in the concept of carrying capacity and the Malthusian gloom and doom that is still very much engrained in the narrative of the environmental movement.  So it was with keen interest that I read this past week an article in the NYT by Erle Ellis, a professor of geography and environmental studies at University of Maryland, who pooh-poohs the Malthusians of our time and argues that human overpopulation is not an obstacle to sustaining life on earth.  Ellis argues,

Many scientists believe that by transforming the earth’s natural landscapes, we are undermining the very life support systems that sustain us. Like bacteria in a petri dish, our exploding numbers are reaching the limits of a finite planet, with dire consequences. Disaster looms as humans exceed the earth’s natural carrying capacity. Clearly, this could not be sustainable.

This is nonsense.  Even today, I hear some of my scientific colleagues repeat these and similar claims — often unchallenged. And once, I too believed them. Yet these claims demonstrate a profound misunderstanding of the ecology of human systems. The conditions that sustain humanity are not natural and never have been.  Since prehistory, human populations have used technologies and engineered ecosystems to sustain populations well beyond the capabilities of unaltered “natural” ecosystems.

The evidence from archaeology is clear. Our predecessors in the genus Homo used social hunting strategies and tools of stone and fire to extract more sustenance from landscapes than would otherwise be possible.  And, of course, Homo sapiens went much further, learning over generations, once their preferred big game became rare or extinct, to make use of a far broader spectrum of species. They did this by extracting more nutrients from these species by cooking and grinding them, by propagating the most useful species and by burning woodlands to enhance hunting and foraging success.

Even before the last ice age had ended, thousands of years before agriculture, hunter-gatherer societies were well established across the earth and depended increasingly on sophisticated technological strategies to sustain growing populations in landscapes long ago transformed by their ancestors.

The planet’s carrying capacity for prehistoric human hunter-gatherers was probably no more than 100 million. But without their Paleolithic technologies and ways of life, the number would be far less — perhaps a few tens of millions. The rise of agriculture enabled even greater population growth requiring ever more intensive land-use practices to gain more sustenance from the same old land. At their peak, those agricultural systems might have sustained as many as three billion people in poverty on near-vegetarian diets.

The world population is now estimated at 7.2 billion. But with current industrial technologies, the Food and Agriculture Organization of the United Nations has estimated that the more than nine billion people expected by 2050 as the population nears its peak could be supported as long as necessary investments in infrastructure and conducive trade, anti-poverty and food security policies are in place. Who knows what will be possible with the technologies of the future? The important message from these rough numbers should be clear.  There really is no such thing as a human carrying capacity.  We are nothing at all like bacteria in a petri dish.

Why is it that highly trained natural scientists don’t understand this?  My experience is likely to be illustrative. Trained as a biologist, I learned the classic mathematics of population growth — that populations must have their limits and must ultimately reach a balance with their environments. Not to think so would be to misunderstand physics: there is only one earth, of course!

It was only after years of research into the ecology of agriculture in China that I reached the point where my observations forced me to see beyond my biologists’s blinders. Unable to explain how populations grew for millenniums while increasing the productivity of the same land, I discovered the agricultural economist Ester Boserup, the antidote to the demographer and economist Thomas Malthus and his theory that population growth tends to outrun the food supply. Her theories of population growth as a driver of land productivity explained the data I was gathering in ways that Malthus could never do. While remaining an ecologist, I became a fellow traveler with those who directly study long-term human-environment relationships — archaeologists, geographers, environmental historians and agricultural economists.

The science of human sustenance is inherently a social science. Neither physics nor chemistry nor even biology is adequate to understand how it has been possible for one species to reshape both its own future and the destiny of an entire planet. This is the science of the Anthropocene. The idea that humans must live within the natural environmental limits of our planet denies the realities of our entire history, and most likely the future. Humans are niche creators. We transform ecosystems to sustain ourselves. This is what we do and have always done. Our planet’s human-carrying capacity emerges from the capabilities of our social systems and our technologies more than from any environmental limits.

Two hundred thousand years ago we started down this path. The planet will never be the same. It is time for all of us to wake up to the limits we really face: the social and technological systems that sustain us need improvement.

There is no environmental reason for people to go hungry now or in the future. There is no need to use any more land to sustain humanity — increasing land productivity using existing technologies can boost global supplies and even leave more land for nature — a goal that is both more popular and more possible than ever.

The only limits to creating a planet that future generations will be proud of are our imaginations and our social systems. In moving toward a better Anthropocene, the environment will be what we make it.

While Ellis and I are in agreement about the indomitable capacity for humans to extend and redefine the very concept of their own sustainability, the ecology of human systems is nonetheless integrally linked to natural systems and inescapable biological norms.  It’s axiomatic that humans, like any other biological creature, cannot live without adequate food, air, water, and shelter to survive.  To the extent the human population or its many sub-populations compromise any of these, we are subject to the same harsh realities of animal population dynamics.  We need not look any farther than the famines and mass starvations throughout Africa.

Ellis’s argument presupposes that humans and our social institutions are capable of deploying science and technology ad infinitum to alter the environment for our sustained needs.  His argument is also predicated on a belief that humans will respond rationally to legitimate threats to life sustaining systems.  Not always the case.   And while the theoretical possibilities of his argument are plausible, the whole premise of his argument appears based on unfounded optimism in social systems and assumptions which governed historically smaller and disparate human populations.  And while human carrying capacity is difficult, if not impossible, to define with precision, as that line is pushed ever outward, the social mechanisms upon which Ellis has such faith will only be able to save us from the same fate as animals if we possess the capacity and willingness to respond and extricate ourselves from meaningful threats to natural systems  – or engineered systems, for that matter – upon which our wellbeing depends.  I certainly don’t lose sleep at night perseverating over these matters, but I’m less optimistic than Ellis who seems to place great confidence and certitude in our societal makeup to make correct and sustainable decisions. However, the flaws in human nature and the feckless and impotent qualities of postmodern social systems, I believe, subject us to the same biological forces of the wolf and moose.

Lastly, although not part of the biological equation, I would also contend that there is an aesthetic element of human existence not addressed in Ellis’s theory and for which science and technologies do not offer satisfactory answers.  As Roger Scruton has long argued, while aesthetics may be immaterial to the biological, it is elemental to the spiritual.  And while humanity would certainly survive without wilderness, that’s not the type of world that I wish to live in, nor would I want that for my children and those who are to follow in our footsteps 100 or 1000 years from now.

(Thanks to Tracy Mehan for forwarding this article)