The Struggle for Existence by G. F. Gause A Classic in Mathematical Biology and Ecology FOREWORD For three-quarters of a century past more has been written about natural selection and the struggle for existence that underlies the selective process, than perhaps about any other single idea in the whole realm of Biology. We have seen natural selection laid on its Sterbebett, and subsequently revived again in the most recent times to a remarkable degree of vigor. There can be no doubt that the old idea has great survival value. The odd thing about the case, however, is that during all the years from 1859, when Darwin assembled in the Origin of Species a masterly array of concrete evidence for the reality of the struggle for existence and the process of natural selection, down to the present day, about all that biologists, by and large, have done regarding the idea is to talk and write. If ever an idea cried and begged for experimental testing and development, surely it was this one. Yet the whole array of experimental and statistical attempts in all these years to produce some significant new evidence about the nature and consequences of the struggle for existence is pitifully meager. Such contributions a3 those of Bumpus, Weldon, Pearson, and Harris are worthy of all praise, but there have been so very, very few of them. And there is surely something comic in the spectacle of laboratories overtly embarking upon the experimental study of evolution and carefully thereafter avoiding any direct and purposeful attack upon a pertinent problem, the fundamental importance of which Darwin surely established. At the present time there is abundant evidence of an altered attitude; and particularly among the younger generation of biologists. The problem is being attacked, frontally, vigorously and intelligently. This renewed and effective activity seems to be due primarily to two things: first, the recrudescence of general interest in the problems of population, with the accompanying recognition that population problems are basically biological problems; and, second, the realization that the struggle for existence and natural selection are matters concerning the dynamics of populations, birth rates, death rates, interactions of mixed populations, etc. These things were recognized and pointed out by Karl Pearson many years ago. His words, however, went largely unheeded for a long time. But in the last fifteen years we have seen more light thrown upon the problems of population by the work of such mathematicians as Lotka and Volterra, such statisticians as Yule, and such experimentalists as Allee and Park, than in the entire previous history of the subject. There can be no doubt of the fact that population problems now constitute a major focal point of biological interest and activity. The author of the present treatise, Dr. G. F. Gause (who stands in the front rank of young Russian biologists, and is, it gives me great pleasure and satisfaction to say, a protege of my old student and friend, Prof. W. W. Alpatov) makes in this book an important contribution to the literature of evolution. He marshals to the attack on the old problem of the consequences of the struggle for existence the ideas and the methods of the modern school of population students. He brings to the task the unusual and most useful equipment of a combination in his own person of thorough training and competence in both mathematics and experimental biology. He breaks new ground in this book. It will cause discussion, and some will disagree with its methods and conclusions, but no biologist who desires to know what the pioneers on the frontiers of knowledge are doing and thinking can afford not to read it. I hope and believe that it is but the beginning of a series of significant advances to be made by its brilliant young author. Raymond Pearl. Department of Biology, School of Hygiene and Public Health, The Johns Hopkins University. AUTHOR'S PREFACE This book is the outcome of a series of experimental investigations upon which I have been engaged for several years past. In these experiments an attempt was made to make use of all the advantages of the controlled study of the struggle for existence in the laboratory with various organisms low in the evolutionary scale. It became evident that the processes of competition between different species of protozoa and yeast cells are sometimes subject to perfectly definite quantitative laws. But it has also been found that these processes are extremely complicated and that their trends often do not harmonize with the predictions of the relatively simple mathematical theory. There is also a continued need for attack upon the problems of the struggle for existence along the lines of experimental physiology and biology, even though the results obtained cannot yet be adequately expressed in mathematical terminology. I wish to express my sincere thanks to Professor W. W. Alpatov for interest in the experimental investigations and for valuable suggestions. To Professor Raymond Pearl I am deeply indebted for great assistance in the publication of this book, without which it could never have appeared before the American reader. I am also grateful to the Editors of The Journal of Experimental Biology and Archiv fur Protistenkunde for permission to use material previously published in these periodicals. G. F. Gause. Laboratory of Ecology, Zoological Institute, Malaia Bronnaia 12, Kv. 33. November, 1934 Chapter I THE PROBLEM (1) The struggle for existence is one of those questions which were very much discussed at the end of the last century, but scarcely any attempt was made to find out what it really represents. As a result our knowledge is limited to Darwin's brilliant exposition, and until quite recently there was nothing that we could add to his words. Darwin considered the struggle for existence in a wide sense, including the competition of organisms for a possession of common places in nature, as well as their destruction of one another. He showed that animals and plants, remote in the scale of nature, are bound together by a web of complex relations in the process of their struggle for existence. "Battle within battle must be continually recurring with varying success," wrote Darwin, and "probably in no one case could we precisely say why one species has been victorious over another in the great battle of life.... It is good thus to try in imagination to give to any one species an advantage over another. Probably in no single instance should we know what to do. This ought to convince us of our ignorance on the mutual relation of all organic beings; a conviction as necessary as it is difficult to acquire. All that we can do, is to keep steadily in mind that each organic being is striving to increase in a geometrical ratio; that each at some period of its life, during some season of the year, during each generation or at intervals, has to struggle for life and to suffer great destruction" ('59, pp. 56-57). (2) But if our knowledge of the struggle for existence has since Darwin's era increased to an almost negligible extent, in other domains of biology a great progress has taken place in recent years. If we look at genetics, or general physiology, we find that a decisive advance has been made there, after the investigators had greatly simplified their problems and taken their stand upon the firm basis of experimental methods. The latter presents a particularly interesting example about which we would like to say a few words. We mean the investigations of the famous Russian physiologist I. P. Pavlov, who approached the study of the nervous activity of higher animal by thoroughly objective physiological methods. As Pavlov ('23) himself says, it is "the history of a physiologist's turning from purely physiological questions to the domain of phenomena usually termed psychical." The higher nervous activity presents such a complicated system, that without special experiments it is difficult to obtain an objective idea of its properties. It is known, firstly, that there exist constant and unvarying reflexes or responses of the organism to the external world, which are considered as the especial "elementary tasks of the nervous system." There exist besides other reflexes variable to an extreme degree which Pavlov has named "conditional reflexes." With the aid of carefully arranged quantitative experiments in which the animal was isolated in a special chamber, all the complicating circumstances being removed, Pavlov discovered the laws of the formation, preservation and extinction of the conditional reflexes, which constitute the basis for an objective conception of the higher nervous activity. "l am deeply, irrevocably and ineradicably convinced, says Pavlov, that here, on this way lies the final triumph of the human mind over its problem--a knowledge of the mechanism and of the laws of human nature." (3) The history of the physiological sciences for the last fifty years is very instructive, and it shows distinctly that in studying the struggle for existence we must follow the same lines. The complicated relationships between organisms which take place in nature have as their foundation definite elementary processes of the struggle for existence. Such an elementary process is that of one species devouring another, or when there is a competition for a common place between a small number of species in a limited microcosm. It is the object of the present book to bring forward the evidence, firstly, that in studying the relations between organisms in nature some investigators have actually succeeded in observing such elementary processes of the struggle for existence and, secondly, to present in detail the results of the author's experiments in which the elementary processes have been investigated in laboratory conditions.