The Human Animal

Spiraling towards explosion

we talk loudly with our mouths full,

not suspecting insurmountable obstacles

that await--we take advantage of boxed food as taste

is slowly forgotten.

The lichen trees are gone now, and the reindeer slowly died,

their cries drowned out by the echo of a thousand T.V.

dinner feasts.

I recently had the pleasure of attending a stimulating lecture entitled "The Human Animal: Population Growth and Sustainability," presented by zoologist and bioanthropologist, Andrea Siatkowski. Andrea pointed out that in spite of the fact that we human beings like to think of ourselves as unique and remarkable, we are still biological entities, members of Earth's global ecosystem, and are therefore subject to all of its laws and constraints.

Andrea noted that normally in a balanced ecosystem, the population of each species is maintained fairly constant due to sets of checks and balances that prevent net population growth. If a species overcomes one of these checks, for example, by obtaining increased amounts of a crucial food source, then the population will grow, initially at exponential rates, until some new set of checks and balances again brings it under control. No species can continue to increase in numbers indefinitely as some essential resource will eventually become limiting. Since humans cannot live in a dormant state, as can bears, which hibernate, or produce dormant life forms such as seeds or spores, as can plants, fungi and bacteria, the lack of food or any other essential resource spells almost immediate death.

The consequences of exponential growth are far reaching. During a period in which one species undergoes growth, the entire ecosystem becomes unstable, giving rise to a non-sustainable use of resources. An early consequence will be disruption of the food chain for the entire ecosystem, and such a disturbance always leads to massive organismal death. This means that the entire local biosphere can be affected.

Since no population can continue to expand indefinitely, the use of a species' resource base sooner or later promotes growth reduction. If the population increases to a degree that is in excess of the carrying capacity of the environment, then as soon as an essential resource is gone, the population must decline because life of the species depends on that resource. Only if the species can be rapidly regenerated can a potential crash be avoided. Thus, for most organisms that lack the ability to generate a dormant resting state, exponential growth is invariably followed by a sharp decline.

Examples of this type of behavior have been observed for bacteria, fungi, plants, insects, and virtually all types of large animals. A well-documented example is provided by reindeer on St. Matthew Island in the Bering Sea off the coast of Alaska. In 1944, a small herd of 29 majestic reindeer (24 females and 5 males) were brought to the island by the U.S. Coast Guard. Since there were ample food sources and no predators, their numbers increased exponentially. By 1957, their numbers had increased to 1,350 and the body weight of the average animal exceeded that of domestic reindeer herds by 25% for females and nearly 50% for males. The population continued to increase due to the excellent quality and quantity of forage. Because the birth rate remained high, and the mortality rate remained low, exponential increase continued. In 1963 there were 6,000 animals on the island. The density was 47 animals per square mile.

Although the numbers had increased to this point without obvious consequences, several signs indicated that a pending crisis was around the corner. The average body weight of the reindeer was dropping, as was the ratio of fawns to adults. These changes were attributed to changes in requisite resources in the ecosystem. For example, lichens, an important component of the winter diet, had been largely consumed. Then when the snows hit in the late winter months of 1963, almost the entire herd of 6,000 died of starvation. Interestingly, all but one of the 43 survivors left in 1966 were females, indicating that although males had increased in weight more than the females in times of plenty, they were far more vulnerable to starvation conditions.

The pattern of population growth and die-off documented for the reindeer herd on St. Matthew Island has been observed repeatedly for many different types of plant and animal species in many different locations and under a variety of conditions. The best-documented cases resulted from controlled experiments in which a single species was introduced into an otherwise unperturbed but closed ecosystem. In most such cases, the decline phase following exponential growth was due to the loss of an essential resource. In other cases, however, the introduction of a predator, sometimes disease-causing micropredators, has promoted the decline phase. Regardless of the cause, the greater the overshoot, the greater the crash.

The relevant question is: Do these principles apply to the human population? Throughout most of the Stone Age, up until about 10,000 BC, there were less than one million people on Earth, less than the current population of San Diego. Then during the Bronze and Iron Ages, with the advent of agriculture and animal domestication, the population gradually increased until by 1 AD, about 100 million people inhabited the Earth. Nevertheless, the increase was moderate compared to what was to follow.

In the middle ages, the Black Death, due to a single micropredator, the plague bacterium Yersinia pestis, dramatically reduced the world human population. But then, with the advent of science, modern medicine and industrialization, the population began its current exponential rise, increasing to the present value of 6.3 billion. Technology may have increased the human carrying capacity of the Earth, contributing very substantially to personal affluence. However, it has also increased resource consumption and our impact on the environment. Societies having access to advanced technologies consume far more resources than more "primitive" societies. For example, the average American consumes three times more resources than the average Italian, 12 times more than the average Brazilian, 36 times more than the average East Indian, and 240 times more than the average Chadian. Thus, the more affluent we become, the greater our impact on the environment is per person, due both to resource consumption and to pollution.

Although the human growth rate is now slowing slightly, the population increase is still astronomical. There are more than 250,000 more human births than deaths every day, which equates to an increase of 10,000 people per hour or 3 per second! Thus, every day there are 250,000 more human mouths to be fed. Since agricultural productivity has been declining worldwide since 1980, and many other resources are being consumed faster than they can be replenished, we may be headed for a population crash.

It doesn't matter what new technologies are developed to try to alleviate the pending shortages of food and other resources. Technological advances may delay the inevitable outcome of exponential growth, but they cannot prevent it. Exponentially growing populations usually overshoot their environment's carrying capacity before experiencing population losses, and the greater the overshoot, the greater the crash. Fluctuations in environmental conditions can precipitate the downward spiraling of the population in advance of complete resource depletion.

Combinations of conditions can contribute to this spiral. In the case of the pending human crisis, these conditions are likely to include global warming, drought, and agricultural decline due to insufficient water supplies, erosion and increased soil salinity. Species extinction, and increased incidences of drug resistant bacterial and viral diseases that affect domestic plants and animals as well as humans, may also play major roles. During the decline phase, death rates will exceed birth rates by many fold, just as for the 1963 reindeer population on St. Matthew Island. It is possible that a combination of global warming, starvation, pestilence, and the consequent deterioration of social order will cause near or even complete extinction of the human race.

In concluding her talk, Andrea pointed out that a rational self-imposed alternative involving birth control and environmental protection would be preferable to the predicted suffering and mass death. Yet implementation of this solution seems to be as far away as it was 50 years ago when the consequences of our population explosion were first clearly recognized. If the human population is not committed to the future of the planet, then parents can expect their offspring to be faced with potentially insurmountable problems none of us have had to face. The great challenge for us results from the fact that the choices are ours to be freely made. Can we make the right ones?

Further Reading