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Evolution and the Genetics of Populations, Volume 2: Theory of Gene Frequencies
"Wright's views about population genetics and evolution are so fundamental and so comprehensive that every serious student must examine these books firsthand. . . . Publication of this treatise is a major event in evolutionary biology."-Daniel L. Hartl, BioScience
520 pages, Paperback
First published January 1, 1984
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September 27, 2024
AN IMPORTANT WORK BY A FOUNDER OF POPULATION GENETICS
Sewall Wright (1889-1988) was an American geneticist known as one of the founders of population genetics, an important step in the development of modern evolutionary theory. The first volume of this series is 'Evolution and the Genetics of Populations: Genetics and Biometric Foundations Vol. 1,' and the third volume is 'Evolution and the Genetics of Populations, Volume 3: Experimental Results and Evolutionary Deductions.'
He wrote in the Introduction to this 1969 book, "Volume 1 of this treatise was concerned with the genetic and biometric foundations on which population genetics must be built. Since the emphasis here is to be on higher organisms, most emphasis will be placed on diploids, but some attention must be given to the haploid phase, to sex-linked lock, and to polysomic lock and polyploids... Chromosome aberration as a factor in evolution will be largely deferred until volume 3, because it does not lend itself to either determinate or stochastic mathematical treatment, to which volume 2 is to be devoted... The relations of genes to characters of the organisms and ultimately to selection ... will be of primary importance in the present volume."
He notes, "Such evolutionary processes as mutation, immigration, selection, and inbreeding seem at first sight to be so different in nature that quantitative comparisons of effects would be impossible. They may, however, be brought under a common viewpoint by measuring each by its effect on gene frequency much as physical phenomena of the most diverse sorts may be reduced to a common quantitative basis by measuring their capacities to do work." (Pg. 24)
He adds, "It is evident that any attempt at complete mathematical formulation must ordinarily lead to extreme complexity and that simplifying assumptions are necessary in order to obtain an understanding of the essential effects of each complication." (Pg. 29)
He explains, "In dealing with mating systems... it was pointed out that the concept of 'effective population number' is a useful one for comparative purposes. This concept becomes a practical necessity in dealing with natural populations. It is obvious that some sort of abstraction must always be made from crude enumerations to obtain the most significant population number from the standpoint of the effects of inbreeding... Such effects depend primarily on the number of individuals of reproductive age per generation, not on the total of all ages. There is the further complication that those of reproductive age may differ enormously in productivity. The sex ration must be taken into account. There is also the difficult problem of overlapping generations in most species." (Pg. 211)
He admits in his discussion of The Steady State Distributions under Mutation and Immigration that "These are, of course, all highly idealized situations, never fully realized in nature." (Pg. 355)
He observes, "It is by no means certain that even a rather strongly favorable individual mutation will be fixed. It is indeed much more likely that it will be lost by accidents of sampling during the period in which it is carried by very few individuals." (Pg. 377)
He summarizes, "Throughout this volume, the genetic compositions of populations have been discussed almost wholly in terms of gene frequencies. The conclusions can be applied to natural and experimental populations insofar as the frequencies of genes are determinable. Unfortunately, many of the most important characters in either sort of population are continuously varying ones in which gene frequencies cannot be determined. The first step in bridging the gap is the analysis of the phenotypic variability of such characters into components that are of genetic significance." (Pg. 487-488)
This is an important work for those interested in the development of evolutionary theory.
Sewall Wright (1889-1988) was an American geneticist known as one of the founders of population genetics, an important step in the development of modern evolutionary theory. The first volume of this series is 'Evolution and the Genetics of Populations: Genetics and Biometric Foundations Vol. 1,' and the third volume is 'Evolution and the Genetics of Populations, Volume 3: Experimental Results and Evolutionary Deductions.'
He wrote in the Introduction to this 1969 book, "Volume 1 of this treatise was concerned with the genetic and biometric foundations on which population genetics must be built. Since the emphasis here is to be on higher organisms, most emphasis will be placed on diploids, but some attention must be given to the haploid phase, to sex-linked lock, and to polysomic lock and polyploids... Chromosome aberration as a factor in evolution will be largely deferred until volume 3, because it does not lend itself to either determinate or stochastic mathematical treatment, to which volume 2 is to be devoted... The relations of genes to characters of the organisms and ultimately to selection ... will be of primary importance in the present volume."
He notes, "Such evolutionary processes as mutation, immigration, selection, and inbreeding seem at first sight to be so different in nature that quantitative comparisons of effects would be impossible. They may, however, be brought under a common viewpoint by measuring each by its effect on gene frequency much as physical phenomena of the most diverse sorts may be reduced to a common quantitative basis by measuring their capacities to do work." (Pg. 24)
He adds, "It is evident that any attempt at complete mathematical formulation must ordinarily lead to extreme complexity and that simplifying assumptions are necessary in order to obtain an understanding of the essential effects of each complication." (Pg. 29)
He explains, "In dealing with mating systems... it was pointed out that the concept of 'effective population number' is a useful one for comparative purposes. This concept becomes a practical necessity in dealing with natural populations. It is obvious that some sort of abstraction must always be made from crude enumerations to obtain the most significant population number from the standpoint of the effects of inbreeding... Such effects depend primarily on the number of individuals of reproductive age per generation, not on the total of all ages. There is the further complication that those of reproductive age may differ enormously in productivity. The sex ration must be taken into account. There is also the difficult problem of overlapping generations in most species." (Pg. 211)
He admits in his discussion of The Steady State Distributions under Mutation and Immigration that "These are, of course, all highly idealized situations, never fully realized in nature." (Pg. 355)
He observes, "It is by no means certain that even a rather strongly favorable individual mutation will be fixed. It is indeed much more likely that it will be lost by accidents of sampling during the period in which it is carried by very few individuals." (Pg. 377)
He summarizes, "Throughout this volume, the genetic compositions of populations have been discussed almost wholly in terms of gene frequencies. The conclusions can be applied to natural and experimental populations insofar as the frequencies of genes are determinable. Unfortunately, many of the most important characters in either sort of population are continuously varying ones in which gene frequencies cannot be determined. The first step in bridging the gap is the analysis of the phenotypic variability of such characters into components that are of genetic significance." (Pg. 487-488)
This is an important work for those interested in the development of evolutionary theory.
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