There are about five billion more people on the planet now than when Thomas Malthus first published his An Essay on the Principle of Population in which he posited his dismal theory of population growth. His theory, which is echoed today by many in the environmental science community, is that an unchecked rise in the human population on Earth will place our species in an unsustainable state with our natural environment. His fear was if the human population continued to rise as it had been for the last two thousand years, we would eventually exhaust all of our natural resources and succumb to a self-induced state of population decline and misery. With a world population now at around 6.5 billion, if his prediction is going to come true, it will do so soon. The solution some experts propose is to attempt to achieve a state of population equilibrium, or what they call the optimum human population size. This idea, however, is ripe with controversy and philosophical quandary. It is the author’s opinion that it is in the human race’s own self interest to examine our behavior in our environment and actively choose the path of sustainability. This essay will examine what it would mean for the human race to attain optimum human population size.

First, we should examine the current world population statistics. At present the global population is a little over 6.5 billions people. Current trends suggest that we have passed the level of highest population growth, which occurred in 1968, and now are experiencing a global decline in population growth. It is predicted that the world population will plateau at around 9 billion by 2050 (US Census). An important trend to note, however, is that birthrates are declining more rapidly in developed nations than in undeveloped nations, which is leading to the population of undeveloped nations representing a larger percentage of the world’s population.

This trend demonstrates a very interesting facet of human reproductive behavior. It would seem that it is possible quantify the “advancement” of the human species by its birthrate. The more technologically advanced a society is, the more of an emphasis is placed on the individual and less cultural emphasis is placed on reproduction. To give an example of how this trend is manifests it self we can look at the effect of infant mortality rate on birthrate. With the advent and global proliferation of modern medical technology infant mortality rates are declining worldwide. According to the World Health Organization, this is the primary reason for the slowing population growth. While it seems counterintuitive, it makes sense. The higher the infant mortality rate is in a country, the more cultural emphasis will be placed on having many children. This is especially true in poverty stricken nations where more children means more support for struggling families. Villagers in India, for example, will have six to eight children to that they can be assured that two or three will survive and stay home to take care of their parents in their old age (Southwick164).

This infant mortality/population growth trend adds weight to the argument that an optimum human population size is naturally desired. Indeed, it is reasoned that the plateau in global population is not due to the lack of resources but to the education of women. Further evidence of this can be seen in the population trends in European countries. In these countries, fertility rates are dropping below 2.1 children per woman, what is considered necessary for a society to maintain its population. A fertility rate of 1.33 in Italy, for example, will potentially cause the country to decrease in population by 1/3 by 2050 (BBC). The two trends seen here introduce a very interesting relationship between technology, culture and population. Technologies that preserve human life lead to a cultural shifts that end up self-regulating a population.

So, what is the significance of nine billion being the population we will plateau at? Is this optimum human population, or is it simply arbitrary that human technological progress has allowed for population growth to reach this level before cultural changes began to temper global population?

To understand this question further it helps to look back at the human species before the most pervasive cultural trait, agriculture, took root. It is theorized by some that the global population of 4-5 million was the ideal global population for the hunter gathering Homo sapiens. Evidence for this is that the global human population did not rise higher than that for about two million years before the advent of agriculture (Ponting 37). Is there an equivalent ideal global population for the farming homo sapiens? More specifically, does this equilibrium population perhaps depend on the energy source that is used to support the population, i.e. is there a different optimum population level for the human race has dependant upon fossil fuels than if it were dependent upon solar energy? Those who believe in the idea of optimum human population argue yes, and many say that 9 billion greatly surpasses what would be ideal for humanity.

According to Paul Ehrlich and his camp, the optimum human population size is between 1.5-2 billion people on the planet. By their research “…the present population of 5.5 billion (in 1994), with its resource consumption patterns and technologies, has clearly exceeded the capacity of Earth to sustain it. This is evident in the continuous depletion and dispersion of a one-time inheritance of essential, non-substitutable resources that now maintains the human enterprise (Daily, 1994).” The 1.5-2 Billion number they have come up with is based on what they consider to be ideal average energy consumption for the world. They reason that, at present, world energy use is about 13 terawatts. About 70% of this is used to by about 1/5 of the world population in rich countries with the remaining 4/5 of the world population in developing nations only using 30% of the total world energy. They claim that this total amount of energy use is biophysically unsustainable and the disparity of energy us between rich and poor societies is ethically undesirable (Daily et al).

The fundamental argument that Ehrlich et al. make is that 4.5-6 TW is the ideal amount of energy use for the human species. They conclude that humans can feasibly attain an average energy use of 3 kW per capita in which case 1.5-2 billion people can live on planet earth in a manner that will be sustainable for the future (Daily et al.).

The most readily made critique of this logic is that Ehrlich and Co. do not and cannot know what level of energy use is sustainable. It is entirely possible that new technologies will make it possible for us to continue to extract this high level of energy from our environment and we will never run into a problem. This is the ever-present hope of the tech fix that will get humanity out of any bind. Economic theory dictates that monetary pressures will always sniff out a viable alternative. If this is the case than there simply is nothing for any of us to worry about, everything will work itself out just fine.

But, and this is a big but, what if it doesn’t? What if scientists cannot come up with a more sustainable source of energy? What if the global oil supply becomes so scarce that its prices soar and most of the world cannot afford it? What if fate has dictated that those who believe in an optimum human population of 2 billion need to learn to be careful about what they wish for? These are all the questions of sustainability.

It is hard to blame the proponents of an optimum human population for wanting to put in place a secure plan for the human race. Indeed, it most certainly is necessary for us as humans to listen to our collective conscience and be cautious of the impact we have on our environment. Realistically, however, it is perhaps most important to encourage the trends that we see already in place in human reproductive behavior. The better educated and the healthier a society is, the less pollution they will incur and the lower their birthrate will be. The point of energy consumption, however, is perhaps the one most in need of addressing presently. There is no foreseeable downside to the development of an environmentally friendly, low energy use lifestyle and much effort should be put towards that, especially among the first world countries that are using up the vast majority of the Earth’s natural resources. In conclusion it seems it would be best to focus our collective efforts to address directly the global problems that we fear overpopulation causes. Population decline wont bring better health care and education to those in developing nations, better health care and education will bring about population decline. Indeed, a world where the general population cares that much about the welfare of the rest of the world sounds pretty optimum to me.

Works Cited
Southwick, Charles H., Global Ecology in Human Perspective Ch 15. pp. 159-182 Oxford Univ. Press, 1996.
Dolan, Edwin G., TANSTAAFL: The Economic Strategy for Environmental Crisis Ch 5. Pp. 55-72 1974.
Ponting, Clive. A Green History of the World: The Environment and the Collapse of Great Civilizations. St. Martin's Press, New York, 1991
BBC News “The EU’s Baby Blues” 3/27/2006 Http://news.bbc.co.uk/1/hi/world/europe/4768644.stm
Daily, Gretchen C., Anne H. Ehrlich, Paul R. Ehrlich “Optimum Human Population Size” July 1994
US Census http://www.census.gov/ipc/www/idbnew.html