Overshoot-and-Collapse: A Model for Our Future?

By David L. Brown

One of the most troubling things about the present world situation is the widespread denial that over-population is a problem that threatens the environment of our planet and the very future of humanity. What is it that people don’t understand about: “There are limits to how many people the Earth can support”? Every day we read or hear examples of a wounded and over-exploited planet in retreat before a growing horde of humanity. Fisheries collapsing from aggressive over-fishing … rain forests falling to the roar of chain saws … oil and other energy sources beginning to show signs that they will soon run out. The signals are many and ominous, and yet most people choose to go on as if everything were just fine. It’s business as usual, even though we are metaphoric passengers on the Titanic as it sails on a collision course with a floating ice mountain that is already looming over the bow.

One of the most influential essays ever published in Science Magazine was titled “The Tragedy of the Commons.” Written by Garrett Hardin, it appeared in 1968, the same year that saw the publication of Paul Ehrlich’s “The Population Bomb.” I say “influential,” but like Ehrlich’s book it actually influenced a small proportion of the total population of the planet, mainly scientists and a few enlightened intellectuals.

In that essay, Hardin argues that the Earth is not without limits, that “Space is no escape,” and that “A finite world can support only a finite population: therefore, population growth must eventually equal zero.” He uses the metaphor of an English “commons,” land open to all and on which every herdsman continued to place more cattle or sheep until the carrying capacity of the field was exceeded, whereupon all were ruined.

Hardin’s point came to mind this morning as I read an interesting statistic from Lester Brown in his recent book “Plan B 2.0 — Rescuing a Planet Under Stress and a Civilization in Trouble.” This is a real jaw-dropper, so pay attention. Brown quotes a personal letter from Paul B. MacCready, founder and CEO of AeroVironment, Inc., and the developer of the first solar powered airplane. Someone, in other words, who is environmentally aware and probably fairly proficient with math.

According to Brown, MacCready attempted to calculate the “footprint” of humanity on the Earth through history. He expressed this by comparing the biological mass (weight) of human beings and all of our domesticated animals (pets and livestock) as a percentage of the mass of all vertebrate animals on land and in the air (not including the oceans). Here is what he found:

• At the dawn of agriculture, when humanity was beginning to emerge from the long era of hunting-gathering, a time when people still lived in harmony with Nature, the total biological mass of humanity and any domesticated animals (at that time essentially none) amounted to 0.01 percent of the total mass of the vertebrates of the land and air.

• Today, the mass of all humans and their domesticated animals is equal to 98 percent of the total mass of all vertebrates presently living on land and in the air. That means that only 2 percent is accounted for by all the wild animals and birds, including everything from armadillos to zebras, from condor to hummingbird, from wee little colonies of mice to the dwindling elephants of the African veldt, the few endangered tigers prowling the equally endangered Asian jungles, and the doomed polar bears of the rapidly thawing North.

Think of it! Humanity has gone from existing comfortably in harmony with Nature, representing only a tiny corner of the environment—one part in a thousand—to being along with his companion animals the absolutely dominating lifeforms of the planet. To support ourselves and our animals we have put vast millions of acres of prairie to the plow, drained countless wetlands, paved over entire landscapes, put millions more acres of forest to the chainsaw and axe, and are despoiling the atmosphere with greenhouse gas and toxins.

Thinking again of the “tragedy of the commons,” what does this mean for humanity? There is another anecdote that applies here, an example often used by ecologists to illustrate the process of “overshoot-and-collapse.” They use this term to describe a phenomenon which occurs when a population of animals in a restricted environment becomes capable of breeding without limit. When there are no predators or other factors to hold it in check, the population zooms past the ability of the environment to support it. That leads to the ultimate collapse in the form of a rapid and disastrous die-off. Here is the well-known example of overshoot-and-collapse:

In 1944, toward the end of World War II, the U.S. Coast Guard was maintaining an outpost staffed by 19 men on St. Matthew Island in the Bering Sea. Noticing that the island had a rich cover of lichen, a favored food of reindeer, and desiring to provide a backup food supply for the men in the outpost, the Coast Guard brought a small herd of 29 reindeer to the remote island and released them to feed on the rich supply of lichens.

The following year the outpost was abandoned and the reindeer were left to their own devices until 1957 when U.S. Fish and Wildlife Service biologist David Kline visited the island. He was astonished to find a thriving herd of 1,350 reindeer feeding on a four-inch thick mat of lichens that covered the 128 square mile island. There were no predators such as wolves or polar bears to restrain the growth of the reindeer population and plenty of food to sustain them. For these animals, the “population bomb” was ticking loudly.

Kline revisited the island in 1963, just six years later, to discover that the reindeer population had exploded to around 6,000, a level that was apparently far in excess of the numbers the lichen crop could support. “Overshoot” had taken place, and “collapse” was now inevitable.

Indeed, when Kline returned once more just three years later in 1966, he found the island strewn with the skeletons of dead reindeer and hardly any lichen remaining. He counted just 42 surviving reindeer, 41 females and a “not entirely healthy” male. There were no fawns. By sometime before 1980 the last reindeer was gone.

This example of ecological “overshoot-and-collapse” bears a message for the human race today, for according to more than a few estimates the number of human beings that the Earth is capable of supporting was passed about 25 years ago, about the same time in fact that the last reindeer disappeared from St. Matthew island.

If we can envision the entire planet as having a limited carrying capacity (which is definitely true), and humanity as having exceeded that capacity (which we probably have) and with no where else to go (we have neither more land nor a future in space), then it is more than just a metaphor to compare our situation with that of the reindeer population on St. Matthew Island in about 1963 when the deer population had overshot to an unsustainable level. From that time, with 6,000 reindeer living on a dwindling supply of food, in only three years most of the the collapse had already taken place with the deer population crashing from around 6000 to 42. Little more than a decade later the last of them were gone and the cycle was complete.

In my opinion, this is less a metaphor than an actual working model for what we humans are facing. But there is a difference in that we are not helpless animals living by instinct and chance alone, but a supposedly clever, tool-making species with a vast store of intelligent common knowledge. The Latin name that describes our species, Homo sapiens, loosely translates as “the wise ape.”

So there could be hope for us yet, if only we can apply that wisdom to work our way around the possible collapse that could follow our present state of population overshoot. So far, unfortunately, science and technology have actually contributed significantly to our population growth problem. Can these clever skills and tools be put to work to help mediate the impending collapse? Some seem to think so, but time is running out.

It has been more than 200 years since Thomas Malthus warned of the danger of exponential population expansion, and even today we “wise apes” don’t seem to have gotten the message. Must we wait until the collapse is real and ongoing? Perhaps so. Perhaps it has already begun. Only time will tell whether humankind can meet this greatest of all challenges.

If things do not go well, perhaps another name will be needed for our species. “Homo stupidus” perhaps?

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