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ne of the most striking features of life on Earth is its diversity. Estimates of the total number of species on the planet range as high as 30 million. It has only recently been recognized that human activities-most notably the destruction of tropical forests-may contribute to the extinction of large numbers of species. Many people feel-for a number of reasons, some ethical and some pragmatic-that the resulting loss in biological diversity is detrimental. Consequently, the conservation of biological diversity promises to be among the premier environmental issues of this decade and beyond. As long as resources are limited for the conservation of biological diversity, they must be allocated across conservation projects. To ensure that the allocation is sensible, it is necessary to first measure biological diversity. Convincing people of this necessity is much more difficult than actually constructing a measure. A small but growing number of scientists has begun to address this issue. This article briefly reviews one line of thinking. Although the basic ideas underlying this work are fairly straightforward, the specific measures that have been proposed involve mathematics well beyond the scope of this article. Thinking ahont diversity One measure of species diversity is the number of species in a set. A problem with this measure, which is called richness, is that it does not take into account how dissimilar the species in the set are from each other. For example, most people would agree that a set consisting of five species of mosquito is less diverse than a set consisting of a mosquito, a butterfly, and an ant (let alone a set consisting of a mosquito,
B y A N D R E W R , S 0L 0W an elephant, and a fern). Thus, in qualitative terms, one way to think about diversity is as a dissimilarity. The meaning of the term diversity in this instance differs from its meaning in ecology, in which diversity is a property of the relative
The conservation of biological diversity promises to be among the premier environmental issues of this decade and beyond abundances of species, without regard to the differences between them ( I ) . There are many ways to measure the dissimilarity (or distance) between two species. Distance measures can be based on morphological or behavioral differences, or on more refined methods of DNA analysis. Once such a distance measure is chosen, it seems natural to determine the diversity between a set of two species by measuring the distance between them. In theoretical terms, the central problem in measuring diversity is extending the intuitive notion of distance to more than two objects. Measuring diversity The search for reasonable diversity measures, and there are certainly more than one, can be narrowed by imposing three natural requirements. First, diversity should not be decreased by the addition of a species to a set. Second,
diversity should not be changed by the addition of a sDecies to a set. if the new species is’identical (in the sense of being at zero distance) from a species already in the set. Third, diversity should be increased by an unambiguous increase in distances between species. Despite the simplicity of these requirements, finding measures that satisfy them is not at all easy. The first diversity measure to satisfy these requirements was proposed by Harvard economist Martin Weitzman (2).Weitzman’s measure is defined recursively, in the sense that to calculate the diversity of a set whose size is n, it is necessary to calculate the diversity of sets whose sizes are n-1, which depends in turn on the diversity of sets whose sizes are n-2, and so on. A particularly attractive feature of this measure is that, in the case where a species can be represented in a rooted evolutionary tree (i.e., in technical terminology, the distances are ultrametric), the measure corresponds to the length of the tree. Weitzman’s measure is quite good at capturing pure dissimilarity between species. In practice, however, it has been criticized for being too sensitive to very large genetic distances. My co-worker Stephen Polasky, a Boston College economist, and I took a different approach (Solow, A. R.; Polasky, S., unpublished results). Rather than assume that diversity has intrinsic value, we constructed a simple model in which individual species have a so-called option value, which reflects their potential future use (e.g., in curing cancer). Assuming that genetically similar species tend to share more characteristics, including medicinal ones, than do dissimilar species, we were able to construct a lower bound on the probability that a set of species contains a cure. This Environ. Sci. Technol., Vol. 27, No. 1, 1993 25
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Regulation of Agrochemicals A Driving Force in Their Evolution
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Agrothemmli an0 tne Reg" aory Process Before 1970 me Pentsten1 Seventnrr Impact of Rfqulnons on the ACS Division of POI. t c de cnemostry 0 CO~IPOYOII~PI of R~rwistration on Emtino Pestiriber 0 A Shorl History of Pesticide Reregistration Pesticide Rfqulation in Developing Countries of the bii-Pacifit Reoian e Pesticide Regi5traG.n in Europ e Academic and Government ReSearch Input to the Registration Pmerr 0 Trends in Agmhemical Fourmulation 0 Analytical Chemistry and Pesticide Regulation Influence Of Requlationr on the Nature of Newer Agricultural Chemicals e Biotechnology and New Directionsfor Aorochemids 0 T i e Fate of Pesticides. the Rerfqinration Prrxerr. and the Inmaring Public Concern about Exposure 0 Agrochemicals in the Future
Gin0 J. Marco. Robert M. Hollingworth. and Jack R. Plimmer. Editon 1 9 2 pages (19 9 1 ) Clothbound ISBN 0 - 8 4 1 2 - 2 0 8 9 - 1 $44.95
Paoerbound i S 8 N 0 - 8 4 1 2 - 2 0 8 5 - 9
h m Caveman to Chemist
Circumstances and Achievements
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hat was the connection between early chemistry and magic? What was the logic that made alchemists think they could make gold out of lead? Why were gases not recognized until the 17th century? Why did it take 49 years before Avogadro's hypothesis was accepted? In From Caveman to Chemist, author Hugh Salzberg traces the oddities of chemistry. ex. amining cultural and political influences on the ideas of chemists. He follows the evolution of chemistry from the Stone Age beginnings of ceramics and metallurgy. through the rise and decline of alchemy. to the culmination of dassical chemistry in the late 19th century. Chapters 1 through 9 lead from prehistoric technology. through ancient and medieval science to the study of chemicals and reactions that resulted in the 16th century birth of x i entific chemistry. Subsequent chapters focus on key chemists such as Sala. Boyie. Black. Lavoisier. Dalton. Berzelius. laurent. and Arrhenius as they developed the ideas that led t o classical chemistry and the concepts of molecules. chemical reactions. homology. valence. and molecular formulas and structures. among others. Twenty topical illustrations enhance the text. Six timelines and two maps help readers understand the influences of early history on chemistry, About the Author Hugh W. Salzberg taught chemistry at the City University of New Yolk for 35 years and offered courses in the history of chemistry over a period of 20 years. From Caveman to Chemist reflects his dual passions for chemistry and history and his profound admiration of the great minds that developed the ideas of chemistry, Hugh W. Salzberg Editor 300 pages ( 1 9 9 1 ) Clothbound: i S 8 N 0 - 8 4 1 2 - 1 7 8 6 - 6
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ISBN 0 - 8 4 1 2 - 1 7 8 7 - 4
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