Man Swarm: Human Population Growth

​​"The massive growth in the human population through the 20th century has had more impact on biodiversity than any other single factor."
 --Sir David King, science advisor to the UK government

man swarm dave foreman

Man Swarm: How Overpopulation is Killing the Wild World by Dave Foreman, with Laura Carroll.

The first edition of Man Swarm reached the conservationist community; in this new and updated edition, Dave Foreman and seasoned editor Laura Carroll expand the readership to the masses. This tight second edition: lays out how the overpopulation explosion is still with us, smartly challenges those who don't believe overpopulation is real, shows that overpopulation is solvable, takes an ecological stand on immigration and its reform in the U.S. as part of the solution, and gives tangible ways all people can be part of the solution. 

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Population Growth and Biodiversity

  • Life on Earth began some 4 billion years ago; complex animal life evolved sometime over 500 million years ago.
  • The human population explosion over the last 200 years is the primary driver of today’s mass extinction
  • It is the exhaust of nearly 7 billion humans that causes the greenhouse effect leading to catastrophic global overheating
  • 30 years ago we were widely alarmed by the population bomb and worked to defuse it

…Now the bomb has exploded yet we pretend the population explosion is not a problem


Complex animal life evolved sometime over 500 million years ago. Since that time, life has continually evolved into different groupings of strange and diverse forms. Today, however, is a unique and unprecedented instant during this extraordinarily long history of life. Never before has there been a creature such as us—a being with the ability to rapidly and radically change the world. Only those who are blind to Nature can look around and not see catastrophe as growing thousands of species are pushed into the dawnless night of extinction.

In the half a billion years of complex life, geology reveals five mass extinctions. All were caused by the smash of big extraterrestrial bodies into Earth or by stupendous geological forces. Biologists and conservationists call today’s extinction the Sixth Great Extinction in light of its magnitude. This extinction stands apart, though, because cosmic or geological forces do not cause it.

It has a biological cause.
One species.
Homo sapiens.

Due to its cause, and heeding our moral compass and sense of justice, perhaps we should not call today’s ecological crisis the “Sixth Mass Extinction.” Rather, we perhaps should call it the First Mass Murder of Life.

Never before has a single species escaped out of the confines of its ecosystems to become a global, geological force and then to spread across Earth to almost every ecosystem, and then remake and in many cases waste those ecosystems. Never before has a single species consumed so much of the rest of life into itself.

Never before has the population of a single species exploded instantaneously across the globe.

We have erupted like the burning cinders and poisonous gases of a giant volcano and now cover Earth.

When we were fewer than six billion, ecologists calculated that we were already using over 40 percent of Earth’s Net Primary Productivity (NPP). NPP is the annual sunlight hitting Earth that is converted through photosynthesis for use by life (see box). We are now over six-and-a-half billion. Demographers predict we will soon soar to nine billion or more. When we are that many, how much of NPP will we take? What will be left for everything else? We are doing more than hogging the interest; we are using up Nature’s capital—taking away what is needed to support species most diverse and what is needed to allow evolution to play out its fascinating potential with the wealth of building blocks it has created.

Consequences of Growth

For over two and a half millennia, wise people have seen the destructive consequences of rapid human population growth. These consequences can be sorted into five kinds:

(1) Land abuse and loss of productivity
(2) Depletion of necessary natural resources and conflict over obtaining new sources
(3) Inability to grow enough food, which leads to hunger and famine
(4) Social, economic, and security crises and threats
(5) Harm to wild Nature

So self-absorbed are we that the last consequence is the least mentioned. But it is the most important and long-lasting result of the human population explosion. Of the five, it is the most obvious and well-documented right now. The murder of Earth’s biodiversity and evolutionary potential will alter the future in ways we cannot foresee. Judging by earlier mass extinctions, it can take millions of years for recovery. And this will be the human legacy—to have behaved like an asteroid? Conservationists within the population discussion must stress how the human population explosion kills Earth’s life. Those who claim to love the wild, to love Nature, to love what has birthed us, are proclaiming a false love if they are unwilling to tackle human population growth or at least acknowledge it.

Immigration and Biodiversity
In taking a biodiversity approach to human population growth, our task is to stabilize and then reduce population because it drives the extinction of species, destruction of ecosystems, and production of greenhouse gases. Population growth is population growth whatever its source, whatever its cause, wherever it happens. In the United States, Canada, Australia, Great Britain, and other countries where the cause of population growth is primarily immigration instead of high birth rates, it is necessary for the sake of biodiversity to reduce immigration to no-net-growth levels. Conservationists, speaking as conservationists, should not debate immigration from social, cultural, economic, or justice standpoints. Our job is to show how human population growth from any source harms the beauty, wonder, diversity, and abundance of all life now and in the future.

The Rewilding Institute is working with a variety of conservationists to make population stabilization a goal and high priority for human civilization.

Forthcoming topics:

* How population growth drives the Seven Ecological Wounds, including Catastrophic Climate Change
* Why conservation and environmental groups have retreated from Population Stabilization advocacy
* Resources for Population Explosion and Biodiversity
* Population Growth Facts and Figures
* Immigration and Biodiversity


[Under Construction—more will be added soon, including websites and a few groups.]

As pointed out above, there are five categories into which the problems of population growth can be sorted: 1) Land abuse and loss of productivity; 2) Depletion of necessary natural resources and conflict over obtaining new sources; 3) Inability to grow enough food, which leads to hunger and famine; 4) Social, economic, and security crises and threats; and 5) Harm to wild Nature and loss of biodiversity. We have grouped resources into these five categories and into a general overview of population problems category. Our overriding emphasis is on category five, the harm to wild Nature. For the other categories we include only the most important resources. Please send us suggestions for additional Resources, especially for Biodiversity Loss.

See “Uncle Dave’s Books of the Big Outside” on this website for additional books and longer reviews from which these are adapted.



Overshoot: The Ecological Basis of Revolutionary Change by William R. Catton Jr., Foreword by Stewart Udall (University of Illinois Press, Urbana, 1982). When I’m asked what the best book is about overpopulation and carrying capacity, one book stands out: Overshoot. In “Books of the Big Outside,” I put Overshoot in “Uncle Dave’s Sixpack” of the most important conservation books. Catton looks at human overpopulation from the ecological perspective of carrying capacity and explains clearly the cornucopian myth. Read it! Illustrations, endnotes, index, 298 pages.

Living Within Limits: Ecology, Economics, and Population Taboos by Garrett Hardin (Oxford University Press, NY, 1993). Fearless Garrett Hardin summarized his work of decades and clearly warned of the many terrible consequences of ignoring population growth in this book. It is a rock of a book upon which cornucopian fantasies shatter. Some illustrations, notes and references, index, 339 pages.

The Ostrich Factor: Our Population Myopia by Garrett Hardin (Oxford University Press, NY, 1999). In this relentlessly tough book, Hardin takes on sacred cows of right and left, including immigration. Endnotes, index, 168 pages.

Population Resources Environment: Issues In Human Ecology by Paul R. Ehrlich and Anne H. Ehrlich (W.H. Freeman and Co., San Francisco, 1970). This was a textbook for conservation college courses in the early 1970s, including one I took at UNM. It has more of an environmental than a conservation emphasis, but it ties everything together under population pressure. I don’t know of anything like it today. Aged though this book is, it’s still a valuable resource if you can find it. It certainly shows just how differently overpopulation was seen in 1970 from today! Illustrations, bibliography, index, 383 pages.

The Population Explosion by Paul R. Ehrlich and Anne H. Ehrlich (Simon & Schuster, New York, 1990). A sweeping and authoritative overview. “From global warming to rain forest destruction, famine, and air and water pollution—why overpopulation is our #1 environmental problem.” Endnotes, index, 320 pages.

The Cassandra Conference: Resources And The Human Predicament edited by Paul R. Ehrlich and John P. Holdren (Texas A&M University Press, College Station, 1988). An anthology from a 1985 conference, this book is as realistic and hard-hitting as its title promises. Ehrlich, Garret Hardin, Peter Raven, Stephen Schneider, Donella Meadows, and half-a-dozen other experts are chapter authors. Remarkable for its early attention to global climate change. Index, footnotes, some illustrations, 350 pages.

The Future in Plain Sight: Nine Clues to the Coming Instability by Eugene Linden (Simon & Schuster, NY, 1998). Linden recognizes the role of population growth in causing instability. One of his nine clues is immigration. An excellent study of possible collapse. Index, 282 pages.


United Nations Report – World Population to 2300. Projections, not predictions, of world population and that of individual countries. Based on current and historical trends.

2011 World Population Data Sheet; The World at 7 Billion,” Population Reference Bureau.

Papers available as PDFs

Democracy Cannot Survive Overpopulation, Albert A. Bartlett addresses increasing concerns about the decline of democracy at all levels of government and shows that overpopulation and technology are major causes.

Reflections on Sustainability, Population Growth and the Environment – 2006, Albert A. Bartlett’s contribution to The Future of Sustainability, an anthology edited by Marco Keiner, Swiss Federal Institute of Technology, ETH Zurich; Springer, Dordrecht, The Netherlands, (2006).

Reproduction and the Carbon Legacies of Individuals” by Paul A. Murtaugh and Michael G. Schlax. Shows how human reproductive choices affect fossil dioxide carbon impact on the environment.

Birth Dearth Folly and the 300 Millionth American” by Dave Foreman, Around the Campfire, Issue 2; January 1, 2007. How the so-called “birth dearth” ignores the impact of population growth on biodiversity.

To the Edge of the Universe With Julian Simon” by Dave Foreman, Around the Campfire, Issue 7; March 31, 2007. Uses Simon’s assertion that human population can continue to grow for 7 billion years to show how ridiculous the cornucopian worldview is.

Retreat on Population Stabilization” by Dave Foreman, Around the Campfire, Issue 11; June 5, 2007. The history and politics of why conservation and environmental groups have retreated from calling for population stabilization.

Population or Affluence?” by Dave Foreman, Around the Campfire, Issue 26; March 10, 2011. Adapted from Man Swarm and the Killing of Wildlife, Chapter Ten. We cannot lighten our ecological footprints by checking affluence alone.

The Population Explosion in a Nutshell” by Dave Foreman, Around the Campfire, Issue 30; August 24, 2011. Adapted from Man Swarm and the Killing of Wildlife, Chapter One. Mass extinction and human overpopulation. A Historical and numerical look at the population explosion and what it means to Earth.

Land Abuse


Deserts on the March, Fourth Edition by Paul B. Sears (University of Oklahoma Press, Norman, 1980 (1935). In his most popular work, Sears, a leading conservationist and botanist of the time, used the Dust Bowl to show how American agriculture was destroying the land. This classic deserves reading by today’s conservationists. Index, 261 pages.

Topsoil & Civilization, Revised Edition by Vernon Gill Carter and Tom Dale (University of Oklahoma Press, Norman, 1974 (1955)). Carter and Dale recount the march of history from ancient Egypt to the Dust Bowl as the story of soil erosion. This book is still not out of date. Maps, black & white photos, bibliography, index, 292 pages.

Papers available as PDFs

Conquest of the Land Through Seven Thousand Years” by W.C. Lowdermilk, USDA Soil Conservation Service, February 1948, 39 pages. This pamphlet is one of the towering achievments in understanding how human civilization has wrecked its land base. “In 1938 and 1939, Dr. W. C. Lowdermilk, who was an assistant chief of the U. S. Soil Conservation Service at that time, made an 18-month tour of western Europe, North Africa, and the Middle East to study soil erosion and land use in those areas. The main objective of the tour was to gain information from those areas — where some lands had been in cultivation for hundreds and thousands of years — that might be of value in helping to solve the soil erosion and land use problems of the United States.”

Estimated impact of global population growth on future wilderness extent” by Egon Dumont, Centre for Ecology & Hydrology, Wallingford, UK.

Resource Depletion


The Party’s Over: Oil, War and the Fate of Industrial Societies by Richard Heinberg (New Society Publishers, Gabriola Island, British Columbia, 2003). Maybe the best of the crop of books about running out of oil. Heinberg considers population growth and doesn’t weave corporate-government conspiracies. Nor does he offer easy ways to solve the crisis. He is an honest realist. Illustrations, bibliography, endnotes, index, 274 pages.

Limits to Growth: The 30-Year Update by Donella Meadows, Jorgen Randers, and Dennis Meadows (Chelsea Green Publishing Co., White River Junction, Vermont, 2004). A thorough update to the famous computer study about all sorts of limits to growth. Anthropocentric, rather abstract, and too optimistic, Limits still has lots of useful information and warnings. Many illustrations, well referenced, index, 338 pages.

Hunger and Famine


Outgrowing the Earth by Lester R. Brown (W.W. Norton, New York, 2004). Outgrowing the Earth is about “The food security challenge in an age of falling water tables and rising temperatures.” Lester Brown, of course, is the world’s authority on the subject. The world is going to get hungry probably much faster than we can imagine. The best book on the topic. I really enjoyed it. Maps, illustrations, endnotes, index, 239 pages.

Social, Economic, and Security


Resource Wars: The New Landscape of Global Conflict by Michael T. Klare (Henry Holt, New York, 2002). I learned a lot from this well-crafted book by a realistic security expert. Klare sees the wars and geopolitics of today and tomorrow as being over resources, especially oil and water, and he points out the flash points where things might erupt. Very useful for getting ready for the future. Klare acknowledges the role of overpopulation. Maps, notes, index, appendices, 289 pages.

Blood and Oil: The Dangers and Consequences of America’s Growing Dependency on Imported Petroleum by Michael T. Klare (Henry Holt, New York, 2004). Klare studies the history of the U.S. and the oil states of the Middle East since World War II, and shows the dangers this history and its shortsighted policies have led us into. Maps, graphs, notes, index, 277 pages.

Sands of Empire: Missionary Zeal, American Foreign Policy, and the Hazards of Global Ambition by Robert W. Merry (Simon & Schuster, NY, 2005). Primarily a devastating attack on Neoconservative imperial foreign policy, Merry also takes on the Idea of Progress and forthrightly acknowledges the role of the population explosion in Islamic countries for creating a powder keg. Index, bibliography, notes, 302 pages.


Return of the Population Growth Factor; It’s Impact Upon the Millennium Development Goals” – Report of Hearings by the All Parliamentary Group Population, Development and Reproductive Health. January 2007.


Return of the Population Growth Factor,” by Martha Campbell, John Cleland, Alex Ezeh, and Ndola Prata, Science Vol. 315, 16 March 2007, 1501-1502. British and African public health experts effectively argue that the UN’s Millennium Development Goals (MGDs) are unachievable with current levels of population growth. It’s about time the antipoverty/public health leviathan started paying serious attention to the population explosion again.



Man Swarm and the Killing of Wildlife by Dave Foreman (The Rewilding Institute, NM, 2011). Shows how our human population explosion is driving mass extinction and greenhouse gas pollution. Graphs and tables, footnotes, index, glossary, and Foreword by John Stuart Mill, 276 pages.

The World According to Pimm: a scientist audits the Earth by Stuart L. Pimm (McGraw-Hill, NY, 2001). Pimm, one of the world’s leading ecologists and experts on evolution, tallies how much of Earth’s Net Primary Productivity (NPP) humans use. He clearly, readably, and authoritatively shows that we are using 42% of Earth’s yearly terrestrial biomass production, about one-third of marine NPP, and 50 % of freshwater. This essential book needs to be read by every conservationist. Maps, endnotes, index, 285 pages.

Rewilding North America: A Vision for Conservation in the 21st Century by Dave Foreman (Island Press, Washington, DC, 2004). In the first third of Rewilding, I go into detail about the mass extinction humans are causing, and argue that population growth is a key underlying cause. Endnotes, index, 295 pages.


Articles, Reports, Papers:

Population Explosion and Biodiversity” by Dave Foreman, Around the Campfire #4. Drawing on Crist’s paper (below), I argue that conservationists should stress the population explosion’s impact on biodiversity, rather than on resource depletion and famine. Click here.

Limits-to-Growth and the Biodiversity Crisis” by Eileen Crist, Wild Earth Spring 2001, 62-65. One of the most important papers on population; Crist powerfully and wisely argues that biodiversity, not resource depletion, is the proper focus for conservationists working on population growth. Click here.

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