From Science 273: 297 — “Extinction Rates”
Letters from:
Julian L. Simon
Stuart L. Pimm, et al.
In their 21 July 1995 article, “The future of diversity” (“Frontiers in biology: Ecology,” p. 347), Stuart L. Pimm et al. incorrectly attribute to me the assertion that “one (or a few) species per year” are going extinct. They go on to say that “Simon’s claims ... are not scientifically credible.” In the very book they cite is the following disclaimer (1, p. 206):
It is entirely inaccurate to say, as Mr. Myers does [the book is a debate between Norman Myers and me], that I have made any estimates of extinction rates. I have never written or spoken such a sentence.
My position is as different as can be from what Pimm et al. and others repeatedly say I said, to wit: There only is evidence for one or a few species a year going extinct, mainly birds or mammals. Of course, many other species are going extinct. And it makes common sense that the extinction rate has been increasing both recently and throughout the long sweep of history. But there is no solid evidence about the rate. And there is no evidence at all that the rate has been increasing in the past century; this calls into question Pimm et al.’s assertion that a higher human population has caused a faster rate of extinction.
Julian L. Simon
College of Business and Management, University of Maryland, College Park, MD 20742, USA
References
Response: We are pleased that Simon agrees that “many other species are going extinct.” Simon’s earlier statement was that “existing data on the observed rates of species extinction are almost ludicrously inconsistent with the doomsters’ claims” (1, p. 43). Our article’s figure 2 showed that observed extinction rates are broadly similar across disparate taxa and consistent with the rates of those whom Simon deems “doomsters.” A recent U.S. report corroborates and expands this consistency to include (in increasing order of rate) birds, mammals, tiger beetles, reptiles, dragonflies and damselflies, ferns, conifers, flowering plants, freshwater fish, amphibians, crayfish, and freshwater mussels (2).
We agree that “it makes common sense that the extinction rate has been increasing both recently and throughout the long sweep of history,” but would be very interested to learn of Simon’s alternative explanation for this increase. Of the hundreds of scientists who have documented these extinctions, we are not aware of one who denied that they were caused directly or indirectly by human impact (3).
Stuart L. Pimm
John L. Gittleman
Gareth J. Russell
Thomas M. Brooks
Department of Ecology and Evolutionary Biology, University of Tennessee, 125 Austin Peay Building, Knoxville, TN 37996, USA
References
- N. Myers and J. L. Simon, Scarcity or Abundance (Norton, New York, 1994).
- TNC Priorities for Conservation: 1996 Annual Report Card for U.S. Plant and Animal Species (Nature Conservancy, Arlington, VA, 1996).
- V. H. Heywood, Ed., Global Biodiversity Assessment (Cambridge Univ. Press, Cambridge, UK, 1995).