Demography Made Simple

I have grown weary of listening to radio and TV new announcers discuss the human population problem. I think a primer of a few principles of population arithmetic might be useful to remind us where we ecologists sit in these discussions. The problem centres on the issue of eternal growth and then the transition of any population from a growing one to a stable one. I concentrate here on human populations but the results apply to any long-lived species.

I list four empirical principles of demography.

  1. No population can continue growing without limit. This generalization is rock solid, so it would be good to keep mentioning it to sceptics of the following generalizations.
  2. Populations grow when births and immigration exceed deaths and emigration. If we consider the entire global human population, emigration and immigration disappear since we have not yet colonized space. Populations stabilize when births equal deaths.
  3. A population that moves from a growth phase to a stable phase must change in age structure. Every stable population must contain fewer young persons and more older persons.
  4. These changes in age structure have enormous implications for our requirements for hospitals, doctors, schools, teachers, and social support agencies. These changes are almost completely predicable for humans and should not come as a surprise to politicians.
  5. Pushing the panic button because a particular population like that of Japan is stabilizing and could even decline slightly may be useful for economists wishing for infinite growth but should be recognized as an expected event for every country in the future.

The bottom line is that we have the knowledge and the ability to plan for the cessation of human population growth. Many good books have been written to make these points and we need to keep repeating them. That many people do not understand the simple arithmetic of population change is a worry, and we should all try to communicate these 5 simple principles to all who will listen.

Cafaro, P., and Crist, E. 2012. Life on the Brink: Environmentalists Confront Overpopulation. University of Georgia Press, Athens, Georgia. 342 pp. ISBN: 978-0-8203-4385-3

Daly, H.E., and Farley, J. 2011. Ecological Economics: Principles and Applications. 2nd ed. Island Press, Washington, D.C. 509 pp. ISBN: 978-1-5972-6681-9

Washington, H. 2015. Demystifying Sustainability: Towards Real Solutions. Routledge, New York. 222 pp. ISBN: 978-1138812697

2 thoughts on “Demography Made Simple

  1. Jeremy Fox

    I must be sounding like a broken record, as I’m once again a bit puzzled by your comments Charley. Presumably because I haven’t seen the tv and radio reports that prompted your post. The policy blogs and news sites I frequent are all familiar with your 5 points. So probably I’m puzzled just because I’m not the intended audience for your comments.

    The challenge is that those 5 points on their own don’t have any policy implications, I don’t think. In particular, your point 1 seems much too vague to have any policy implications, except perhaps as an additional (weak) reason to pursue certain policies we’d have wanted to pursue anyway. And the economists I read who are concerned about how Japan’s demography is affecting its economy aren’t concerned because they’re shocked by Japan’s demography (your point 5); they’re not surprised that Japan’s population is declining as its age structure changes. They’re concerned because of the first part of your point 4 (more or less). And so I question how much political or policy traction could be had by simply banging away on these 5 points. But then, I’m no expert on how to influence politics or policy.

    At the risk of shameless self-promotion, I recently read Paul Sabin’s history of the population debates of the 1970s, focusing on the roles of Paul Ehrlich and Julian Simon. I found it very thought-provoking; some comments here:

    1. Charles Krebs Post author

      Jeremy – first of all I think that ecologists do not make policy and their job is to provide evidence. This blog was not directed at ecologists who know these points but at the need to make sure others not trained in ecology do not misuse them. In particular newspaper and media comments on population policy. The current policies of Canada, Australia, and the USA all conflict with item 1 in that every government is committed to indefinite population increase. The details of polices to reach zero population growth are up to the people and governments but the overall goal has implications for immigration policy, reproductive policies and foreign aid. I appreciate that there are excellent economists out there pushing for good policies, and my concern is not to lecture them but to inform the general public and teachers that there are ecological principles that should underlie government policies. But certainly I do not think ecologists knowing these simple points by themselves get any political traction. If I knew how to get political traction, the world would hopefully be quite different. So I beaver away at the subversive level of education. So I agree there is nothing new in these 5 points. They could have been written 50 years ago.


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