Evolution: Selected Papers

I have designed this volume as a companion to "Sewall Wright and Evolutionary Biology" and to Wright's four-volume treatise, "Evolution and the Genetics of Populations". In his treatise, Wright constantly referred to his earlier publications on evolutionary biology. He did not, however, simply summarize these papers, but instead generally began his discussion from where they left off. Much of Sewall Wright and Evolutionary Biology (hereafter referred to as SW&EB) is devoted to an analysis of the background and content of Wright's papers on evolutionary biology. Thus a volume containing a judicious selection of his published papers on evolutionary biology would be a very useful companion to these two works. Wright is one of the most influential evolutionary biologists of the twentieth century, and this volume might also be useful for those merely wishing to have a collection of his papers on that subject. Another compelling reason for publishing a volume of Wright's papers, especially those before about 1950, is that they were little understood at the time of publication, even if widely read. Still Wright enjoyed much prestige as a quantitative population geneticist. The primary reasons for this curious situation are easily seen. Evolutionary biologists in general had very little training in mathematics or specifically in statistics, or in quantitative reasoning generally. Moreover, Wright was rather insensitive to the inability of his audience to follow his quantitative reasoning. Even those with some mathematical training had much difficulty following Wright's idiosyncratic method of path coefficients. Inability to read much more than his introductions and conclusions did not, however, prevent many evolutionists from admiring Wright's quantitative work. As Ernst Mayr and John A. Moore have pointed out on many occasions in letters to me, evolutionary biologists were extremely susceptible to the attractions of quantitative models whose derivations they could not understand. [...] Included in this volume are all of Wright's published papers on evolutionary biology up to 1950 and a selection of those published after that, including two important papers published after the last volume of his treatise (1978; the treatise is hereafter referred to as E&GP). I have included all of the earlier papers because in SW&EB most of my discussion of Wright's published papers concerns the period before 1950; the papers published after 1950 tend to be repetitious of earlier papers or of the later treatise and, being older, the earlier papers are more difficult to locate. I have excluded from this category only the five papers that Wright wrote in collaboration with Theodosius Dobzhansky and published in Dobzhansky's famous series, "The Genetics of Natural Populations," which has recently been republished in its entirety with extensive introductions (Lewontin et al. 1981). I included the two very recent papers because one is Wright's own account of the origins of his shifting balance theory of evolution in nature and the other his analysis of speciation and the theory of punctuated equilibrium, popularized by Niles Eldredge and Stephen Jay Gould (Eldredge and Gould 1972). Wright received more requests for reprints of this last paper than any other he ever published (he was ninety-two when it appeared in print). There was another reason for this pattern of selection of the papers. Continuity versus change is a fundamental theme in the development of an individual scientist's thought and influence. This theme is especially important in Wright's case because he has strongly emphasized the continuity in his thinking about mechanisms of evolution from the mid-1920s to the present. While agreeing with Wright that his thought about evolution has been in many ways remarkably consistent over the years, I argue in SW&EB that in some crucial ways he changed his mind about the mechanisms of evolution, especially concerning the problem of adaptation in relation to random drift and selection. By presenting Wright's papers on evolution in their entirety up to 1950, a comparison of his earlier and later views is possible simply by examining this volume and his E&GP, an exercise that I warmly recommend to anyone interested in the development of Wright's views and their influence in evolutionary biology. Both this introduction and those for the individual papers are very brief because most of the historical background is already in SW&EB; later extensions of the papers are detailed in E&GP. Thus aside from the barest information about each paper, the primary purpose of the introductions is to refer the reader to the pertinent sections of SW&EB and E&GP, where often extensive background may be found. With a few exceptions, the order of presentation of papers in this volume is chronological. For obvious reasons, I have placed first Wright's 1978 paper on the origins of his shifting balance theory. Otherwise, the only departure from strict chronological order comes when papers sharing a basic theme are introduced together, as in the case of Wright's three papers on isolation by distance. All but a few of the papers in this volume were photocopied from reprints that Wright sent out to other biologists. Occasional typesetting errors appeared in the published journals, and Wright corrected these by hand in the reprints he sent to others. Wright's corrections thus appear in these photocopies. The print quality of the original reprints from which the reproductions are taken varies considerably. Many academic journals in the first half of the century operated on minimal budgets; low-quality print was one way to save money. Every effort has been made in this volume to maintain the highest quality in photo reproduction. The variation in the results is therefore a function of variation in the originals. The advantages to scholars of having the originals is enormous, well worth the cost of some variation in print quality. Sewall Wright deserves the credit for this volume. He wrote all of the papers and told me about the origins of each one. He also wrote a detailed critique of the draft version of my introductions to the papers. Our conversations about the background of the papers are recorded on audiotape (and are partially transcribed) and are available at the Library of the American Philosophical Society. [...] [From the Preface]