20 Century

Created 1/24/1997
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Slouching Towards Utopia?: The Economic History of the Twentieth Century

-XXVII. Ecology and Population-

J. Bradford DeLong
University of California at Berkeley and NBER

February 1997

  • Ecology
  • Pollution
  • Managing International Resources
  • Changing the Global Climate
  • How Many People Can the Earth Support?


Human beings' activities have been affecting the rest of the ecology and the global environment since well before the beginnings of recorded history. The appearance of migrants from Siberia to the Americas some fifteen thousand or so years ago was soon followed by the elimination of many of the larger mammals on the American continent: the mammoths, the large predators, and the American horse. The colonization of Australia some forty thousand years ago was followed by the extinction of a similar class of very large marsupials.

Similar extinctions and reductions of range occurred in Eurasia as humans, armed with the then "modern" technologies of fire, fur, and flint, moved into the northern latitudes. Where is the Siberian woolly rhinoceros? Where is the Eurasian mammoth? In myth Hercules fought lions: there are no lions in Greece today, and the range of the lion is restricted to a relatively small belt in the African savannah.

We do not know about the impact of the evolution of humans on the relatively tropical climates of Africa and Asia because humans have been there so long. All we can even roughly track is the impact of the spread of technologically proficient humans--with stone tools, fire, and needles--into north temperate latitudes, and into Australasia and over the Beringia land bridge to the Americas. Everywhere we look humans--even at the stage of fire and tool-using hunter-gatherers have had profound effects on the ecology.

Things have accelerated as human numbers have grown from a few million to six billion, and as human technologies have advanced from hunter-gatherer to agricultural to industrial and post-industrial. Today there is barely a place on the globe where the local ecology is not profoundly affected by the presence of six billion human beings on the planet



Local pollution has always been worst in cities. Pre-industrial cities, however, had pre-industrial pollution: the enormous concentration of human and animal wastes in plces with insufficient runoff. As a result pre-industrial cities were unhealthy places for humans and animals: no pre-industrial city managed to have more births than deaths. All grew in population--all were kept from population collapse and desertion--by migration in from the countryside for those seeking better work or a more exciting (if more disease-ridden) life.

With the industrial revolution the pollution threat changes. Public hygeine improves enormously as sewage systems and modern hospitals make cities, for the first time, healthier places than the countryside. But other threats emerge: industrial rather than pre-industrial pollution. Heavy, poisonous metals in the earth; smog in the air; leaking oil in the water.

In the first century or so of industrialization, industrial pollution was not a menace seen as worth combatting: coal smoke and fouled rivers were seen as signs of prosperity-- smokestacks that failed to belch smoke were signs of depression and unemployment. People were applauded for filling in swamps, not scorned for destroying wetlands.

There is reason to believe that democratic politics are capable of making more-or-less appropriate decisions as to what tradeoffs to make between material production on the one hand and environmental quality improvement on the other. People care about the environment--and are willing to vote for politicians who pledge environmental cleanup once basic material needs have been met.

Managing International Resources


Changing the Global Climate


How Many People Can the Earth Support?


20 Century

Created 1/24/1997
Go to
Brad DeLong's Home Page

Associate Professor of Economics Brad DeLong, 601 Evans
University of California at Berkeley; Berkeley, CA 94720-3880
(510) 643-4027 phone (510) 642-6615 fax