Whether we behave like Caterpillars or whether we behave like Butterflies depends on the stories that we have bought into, which then rule our actions. It has now become commonly accepted lore that human beings have no choice but to be Caterpillars and from this, it logically follows that the sheer number of human beings on the planet is the primary reason for the destruction that we're inflicting on the planet. That is, we are led to believe that all our environmental problems are mainly due to human "overpopulation."
In 1968, Paul and Anne Ehrlich wrote "The Population Bomb," boldly predicting widespread famines in the world during the 1970s and 1980s and recommending drastic measures for curtailing human population across the world. The Ehrlichs' book propelled the population debate into the mainstream and human population growth has remained a popular bugbear for societal ills in some intellectual circles. With the advent of the industrial revolution, human life expectancy has steadily increased with declining death rates and human population has ballooned. In 1800, human population reached 1 billion; it increased to 1.6 billion by 1900 and 6.1 billion by 2000, marking a six-fold increase in 200 years. Human population is currently at 7 billion and it is projected to top out around 10 billion on the high end by 2100 according to UN projections.
Of course, such projections assume that the past is prologue.
While human population increased by a factor of 6 from 1800 to 2000, the inconvenient truth for the population "bombers" is that human consumption of world resources increased by a factor of 64 within the same time frame. Vast numbers of humans are living like the nobility of the past, eating exotic foods from all over the world and traveling vast distances on a frequent basis. Such indulgences use up resources. World consumption, in constant dollars, increased from $400B in 1800 to $1.6T in 1900 to over $25T in 2000 fueling the meteoric rise in human impact on the planet.
As human consumption has grown 64-fold in 200 years, the inequity in consumption between the top and the bottom has also grown, becoming increasingly stark in recent times. The top 20% of humans were responsible for 83% of world consumption circa the year 2000, while the bottom 20% were responsible for just 1.3%. This is a 64-fold difference in impact or footprint at the two ends of the social stratum. Most of the increase in human population is occurring in the bottom 20% of the economic pyramid, with about 80 million additional human beings added to the world population each year, while most of the increase in consumption is occurring at the top.
This sets up an Alphonse-Gaston act between the top and the bottom economic tiers of society with both sides talking past each other as they view the world from their narrow perspectives, while doing nothing about the situation. The people in the top 20% see an overpopulation problem as they are concerned that all these additional people would eventually want to live like them and they know that there certainly aren't enough resources on the planet to accommodate this shift. Furthermore, the people in the top 20% also want to improve their state of affluence constantly, expecting a 3% increase in consumption on an annual basis and firing their political leaders when they are unable to achieve such economic growth. The people in the bottom 20% are aggrieved that every child in the top tier has the same impact as 64 children in the bottom tier and yet the additional children they bring into the world in the bottom tier in a quest for survival and security are somehow construed as a burden on society. After all, the top 1.3 billion people on the planet look like 83 billion people from the perspective of the bottom 20% of the pyramid. And from the perspective of the bottom 20%, those 83 billion people at the top ought to be ashamed when they tell the people below them that there are too many of them.
Our current economic structures exacerbate such disparities. For instance, productivity improvement is supposed to be the constant quest of a technological society, but lately, this has become a euphemism for cutting people out of employment or dumbing them down. Coal mines that used to require thousands of laborers can now be operated with a few people and giant earth moving equipment through the process of mountaintop removal mining. Factories that used to require thousands of people to run can now be operated with automated processes manned by just dozens of people. Such productivity gains improve profit margins for the corporations, but reduce employment for human beings. The only way for people to find employment is for the economy to start making even more stuff and to start peddling it to even more numerous and voracious consumers. It is consumption, the fulfillment of desires, that primarily drives economic growth in the current paradigm. There are even serious books entitled, "Why People Buy Things They Don't Need," to teach marketing professionals how to trigger such desires among their potential customers. American homes have almost tripled in size since the 1950s and yet, the American appetite for "stuff" is such that there is a $20B a year industry to store overflow "stuff" for Americans. And yet, the growth paradigm of our economic well-being requires people to buy even more "stuff." This is why Vice President Joe Biden wrote an Op Ed in the New York Times urging the Chinese and other people in developing countries to stop saving and start consuming in order to drive world economic growth. More than citizens or human beings, people have become consumers, whom President Herbert Hoover characterized as "constantly moving happiness machines, machines which have become the key to economic progress."
But this standard formula for economic progress is running out of steam. And it is up to us who are alive today to recognize that and make a shift in the way we live. Specifically, I consider the 10-30 year olds alive today as the Most Important Generation that ever Lived on Earth (MIGLE) for they need to become Butterflies. Or choose not to change and face intense suffering and possibly, a major mass extinction event in their lifetimes. The members of this generation are Miglets. Our two children are Miglets. At their age, Miglets are prone to be idealistic and are much more likely to lead the way towards such fundamental behavioral shifts.
At present, many Miglets have done all the things that their elders wanted of them, studied hard, got a good education, played by the rules or more likely, never got caught breaking rules, but they haven't found jobs in the present economic environment in America. I know one Miglet who was working at a meat packing plant at minimum wage after a BS in Chemical Engineering. Many Miglets are at home with their parents after getting their degrees, because our corporations have discovered that it is much cheaper to hire Miglets in India or China instead. Meanwhile, the student loans of the Miglets keep piling up. Besides, the salaries in India are also being driven down by the paucity of jobs there as the spiraling race to the bottom is well and truly underway for the Miglets.
There are many intellectuals around the world who believe that this situation is inevitable because the optimum human population of planet Earth is 1-2 billion. But it seems to me that they base their estimates on the current Western way of life or on the life that they are personally leading.
Suppose that our industrial civilization had arisen out of China instead of the West. And imagine that a Chinese "McDonalds" popularized the consumption of Bear-Paw soup and Shark-fin soup throughout the world, instead of the Hamburgers and Fillet-of-Fish that we find peddled in every corner of the globe today. Bear Paw soup is a Chinese delicacy with strong parallels to shark-fin soup. To make bear-paw soup, we cut off the paws of a bear and exhibit the bear outside our restaurant with its bleeding hands so that our customers know that the soup inside is fresh. Only the paws of the bear are used to make the soup while the rest of the bear is discarded after it bleeds to death.
To make shark-fin soup, we cut off the fins of the shark and let the rest of the shark die in the water.
Then the common diet around the world would have involved an order of magnitude more waste than the diet of Hamburgers and Fillet-of-fish that we consider to be normal today. In that case, perhaps, at most 100 million people could be supported in such a lifestyle on this planet. We would have to grow crops to feed small animals to feed the bears, just to cut off their paws and use the paws for human food. We would have to grow crops to feed small fish to feed the sharks, just to cut off their fins and use them for human food.
In such a world, even by 500 BC at the time of the Buddha, the human population would have been too many and completely non sustainable! Therefore, I believe that the intellectuals who contend that the optimum human population on the planet is 1-2 billion are not asking the right question. The question shouldn't be, "What is the optimum human population on the planet if everyone lived like us?" Instead, it is much more productive to address the question, "How should we be living, given that there are 7 billion people and 20-100 million other species on the planet today?"
Just as there is a major disparity in overall consumption between the top and the bottom, there is a similar glaring disparity in fossil energy consumption as well. Fossil fuels such as coal, oil and natural gas are all carbon-based fuels that release energy when they are burnt, but they also convert the stored carbon on land into the gas, Carbon DiOxide (CO2), which accumulates in the atmosphere, blanketing the earth and causing it to warm. Prof. Stephen Pacala of Princeton has calculated that the top 500 million people on the planet are responsible for half the carbon emissions and that these people are actually everywhere. They aren't just in the global North, but they are also found among the top consumers in India, China, Brazil, Russia and the global South. But when we consider consumption on a country by country basis, these top consumers in the global South are able to hide behind the skirts and saris of the poor and present themselves as holier than thou to the rich countries. As a result, negotiations at the United Nations (UN) on controlling atmospheric emissions from burning fossil fuels have been far from effective, because this is truly a grassroots behavioral problem that is not conducive to a country-by-country top-down solution. In our globalized economy, the top consumers in the global South are just as responsible for the world's environmental problems as the consumers in the global North.
At the UN Earth Summit in Rio de Janeiro in 1992, President George H.W. Bush of the United States flatly asserted to the world, "The American Way of Life is Non-Negotiable." This didn't win America many friends in the world community. Said Jayanthi Natarajan, the new Minister for the Environment of India, "There is something fundamentally unfair about countries that have used up all the natural resources and reserves on our planet, turning around and preaching to us about reducing our carbon footprint when with our billion-plus population, we are not even a blip on the radar of carbon emission. Western countries who preach the most have absolutely no intention of cutting their own carbon emission or to rethink about their wasteful economies…”
Meanwhile, the present American way of Life is being exported by corporations to people all over the world. For corporations are not particularly sensitive to where their profits are derived from and want to keep growing them regardless of the consequences to the planet. They may be American corporations, but their loyalty to their bottom line invariably exceeds that to America or to the planet.
And so it goes. The rich people in the world want the poor people to stop having kids, while the poor people want the rich to stop consuming so much. Both sides are mostly interested in getting other people to change.
But the only way to get other people to change is to first change ourselves, to undergo our own personal Metamorphosis.
 Paul R. Ehrlich, "The Population Bomb," Sierra Club and Ballantine Books, 1968. http://www.amazon.com/Population-Bomb-Paul-R-Ehrlich/dp/1568495870. Though Anne Ehrlich was a coauthor on the book and Paul freely admits it, her name does not appear in the book at the publisher's insistence.
 UN long range population projections can be found in http://www.un.org/esa/population/publications/longrange2/WorldPop2300final.pdf
 UN world consumption statistics can be found in the 1996 Human Development Report of the UN Development Project (UNDP). http://hdr.undp.org/en/reports/global/hdr1996/chapters/
 UNDP stats on the disparities in consumption can be found in the 1996 Human Development Report from  and in the 2010 report. http://hdr.undp.org/en/reports/global/hdr2010/ . Dianne Dumanoski has a good treatment of the population vs. consumption debate in Chapter 2 of her book, "The End of the Long Summer: Why We Must Remake Our Civilization to Survive on a Volatile Earth," Crown, July 2009. http://www.amazon.com/End-Long-Summer-Civilization-Volatile/dp/030739607X
 Pamela Danziger, "Why People Buy Things They Don't Need: Understanding and Predicting Consumer Behavior," Kaplan Publishing, 2004. http://www.amazon.com/People-Things-They-Dont-Need/dp/0793186021
 The statistics on the self-storage industry can be found in http://www.selfstorage.org/SSA/Home/AM/ContentManagerNet/ContentDisplay.aspx?Section=Home&ContentID=4228 . The statistics on American home sizes can be found in the NPR report http://www.npr.org/templates/story/story.php?storyId=5525283 .
 Joseph Biden, Jr., "China's Rise isn't our Demise," New York Times, September 7, 2011. http://www.nytimes.com/2011/09/08/opinion/chinas-rise-isnt-our-demise.html
 President Herbert Hoover is reported to have made this statement to a group of advertising executives shortly after taking the oath of office in 1929. Here's a NY Times movie review on the "Century of the Self," that reprints President Hoover's quote: http://movies.nytimes.com/2005/08/12/movies/12self.html
 Gretchen Daily, Anne and Paul Ehrlich calculated the "Optimum Human Population size" to be 1.5 to 2 billion in http://news.stanford.edu/pr/94/940711Arc4189.html. In the Global Biodiversity Assessment of 1995, it was estimated that the earth can support at most 1 billion people at American levels of consumption. Please see Vernon Heywood, Ed., "Global Biodiversity Assessment," 1995. http://www.cambridge.org/gb/knowledge/isbn/item5708206/?site_locale=en_GB .
 Stephen Pacala, "Equitable Solutions to Greenhouse Warming: On the Distribution of Wealth, Emissions and Responsibility WIthin and Between Nations," Presentation to IIASA, November 2007. http://www.iiasa.ac.at/Admin/PUB/podcast/16pacala.pdf
 This particular quote of President George H.W. Bush has been repeated ad nauseum. A good treatment can be found in David R. Loy's paper http://www.interfaithjustpeace.org/pdf/2010/the_nonduality__david_loy.pdf and in Ehrlich and Kennedy, "Millennium Assessment of Human Behavior," Science Magazine, 2005. http://mahb.stanford.edu/wp-content/uploads/2011/08/4-2005-Ehrlich-Kennedy-MAHB-Science.pdf