Mendel's Principles of Heredity

William Bateson, Gregor Mendel, Gregor Mendel, Gregor Mendel

• Publisher: Dover Publications
• Year: 2013
• Print ISBN: 9780486477015
• eBook ISBN: 9780486148373
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

Six years after Charles Darwin announced his theory of evolution to the world, Gregor Mendel began studying the inheritance of traits in pea plants. Mendel's research led to his discovery of dominant and recessive traits and other facts of evolution, which he reported in his groundbreaking 1865 paper, Experiments in Plant Hybridization. His findings languished until 1902, when William Bateson revived interest in the subject with this book, a succinct account of Mendel's heredity-related discoveries. Bateson coined the term "genetics" to refer to heredity and inherited traits, and his rediscovery of Mendel's work forms the foundation of today's field of genetics.
Suitable for biology and general science students at the undergraduate and graduate levels, this volume is essential reading for anyone with an interest in science and genetics. In addition to Bateson's commentary, it features two of Mendel's papers—including the original Experiments—plus a biography of Mendel, a detailed bibliography, and indexes of subjects and authors. Numerous figures complement the text, along with eight pages of color illustrations.

PART I

CHAPTER I

INTRODUCTORY. MENDEL’S DISCOVERY.

Introductory—Some pre-Mendelian Writings—Mendel’s Discovery—Dominant and Recessive—Segregation. Allelomorphism—Homozygote and Heterozygote. Purity of Type.

AMONG the biological sciences the study of heredity occupies a central position. Whether we be zoologists, botanists, or physiologists, the facts of heredity concern us. Upon this physiological function all the rest in some degree depend. Every advance in knowledge of that central function must affect the course of thought along each several line of biological inquiry.

Moreover though, as naturalists, we are not directly concerned with the applications of science, we must perceive that in no region of knowledge is research more likely to increase man’s power over nature. The science of sociology, and in many of its developments the science of medicine also, must of necessity form working hypotheses respecting the course of heredity, and we cannot doubt that a perception of the truth in regard to the function of transmission will greatly contribute to the progress of these sciences. Lastly, to the industrial arts of the breeder of plants or animals, the knowledge we are attempting to provide is of such direct importance that upon this consideration no special emphasis is required. In studying heredity, therefore, we are examining a vital problem of no mean consequence, and those who engage in that work are happy in the thought that they are assisting one of the main advances in natural knowledge.

But though we may approach this study of genetics—to use the modern designation—from so many different sides, it is especially in their bearing on the problem of the evolution of species that the facts have hitherto been most profitably investigated. It was in the attempt to ascertain the interrelationships between species that experiments in genetics were first made. The words “evolution” and “origin of species” are now so intimately associated with the name of Darwin that we are apt to forget that the idea of a common descent had been prominent in the minds of naturalists before he wrote, and that, for more than half a century, zealous investigators had been devoting themselves to the experimental study of that possibility. Prominent among this group of experimenters may be mentioned Koelreuter, John Hunter, Herbert, Knight, Gaertner, Jordan, Naudin, Godron, Lecoq, Wichura—men whose names are familiar to every reader of Animals and Plants under Domestication. If we could ask those men to define the object of their experiments, their answer would be that they were seeking to determine the laws of hereditary transmission with the purpose of discovering the interrelationships of species. In addition to the observation of the visible structures and habits of plants and animals they attempted by experiment to ascertain those hidden properties of living things which we may speak of as genetic, properties which breeding tests can alone reveal. The vast mass of observation thus accumulated contains much that is of permanent value, hints that if followed might have saved their successors years of wasted effort, and not a few indications which in the light of later discovery will greatly accelerate our own progress.

Yet in surveying the work of this school we are conscious of a feeling of disappointment at the outcome. There are signs that the workers themselves shared this disappointment. As we now know, they missed the clue without which the evidence so laboriously collected remained an inscrutable medley of contradictions.

While the experimental study of the species problem was in full activity the Darwinian writings appeared. Evolution, from being an unsupported hypothesis, was at length shown to be so plainly deducible from ordinary experience that the reality of the process was no longer doubtful. With the triumph of the evolutionary idea, curiosity as to the significance of specific differences was satisfied. The Origin was published in 1859. During the following decade, while the new views were on trial, the experimental breeders continued their work, but before 1870 the field was practically abandoned.

In all that concerns the problem of species the next thirty years are marked by the apathy characteristic of an age of faith. Evolution became the exercising-ground of essayists. The number indeed of naturalists increased tenfold, but their activities were directed elsewhere. Darwin’s achievement so far exceeded anything that was thought possible before, that what should have been hailed as a long-expected beginning was taken for the completed work. I well remember receiving from one of the most earnest of my seniors the friendly warning that it was waste of time to study variation, for “ Darwin had swept the field.”

Parenthetically we may notice that though scientific opinion in general became rapidly converted to the doctrine of pure selection, there was one remarkable exception. Systematists for the most part kept aloof. Everyone was convinced that natural selection operating in a continuously varying population was a sufficient account of the origin of species except the one class of scientific workers whose labours familiarised them with the phenomenon of specific difference. From that time the systematists became, as they still in great measure remain, a class apart.

A separation has thus been effected between those who lead theoretical opinion and those who by taste or necessity have retained an acquaintance with the facts. The consequences of that separation have been many and grievous. To it are to be traced the extraordinary misapprehensions as to the fundamental phenomena of specific difference which are now prevalent.

If species had really arisen by the natural selection for impalpable differences, intermediate forms should abound, and the limits between species should be on the whole indefinite. As this conclusion follows necessarily from the premisses, the selectionists believe and declare that it represents the facts of nature. Differences between species being by axiom indefinite, the differences between varieties must be supposed to be still less definite. Consequently the conclusion that evolution must proceed by insensible transformation of masses of individuals has become an established dogma. Systematists, entomologists or botanists for example, are daily witnesses to variation occurring as an individual and discontinuous phenomenon, but they stand aside from the debate ; and whoever in a discussion of evolutionary theory appeals to the definiteness of varietal distinctions in colour for instance, or in form, as recognizable by common observation without mechanical aid, must be prepared to meet a charge of want of intelligence or candour. This is no doubt a passing phase and will end so soon as interest in the problems of evolution is combined with some knowledge of variation and heredity.

Genetic experiment was first undertaken, as we have seen, in the hope that it would elucidate the problem of species. The time has now come when appeals for the vigorous prosecution of this method should rather be based on other grounds. It is as directly contributing to the advancement of pure physiological science that genetics can present the strongest claim. We have an eye always on the evolution-problem. We know that the facts we are collecting will help in its solution; but for a period we shall perhaps do well to direct our search more especially to the immediate problems of genetic physiology, the laws of heredity, the nature of variation, the significance of sex and of other manifestations of dimorphism, willing to postpone the application of the results to wider problems as a task more suited to a maturer stage. When the magnitude and definiteness of the advances already made in genetics come to be more generally known, it is to be anticipated that workers in various departments of biology will realise that here at last is common ground. As we now know, the conceptions on which both the systematists and the speculative biologists have based their methods need complete revision in the light of the new facts, and till the possibilities of genetic research are more fully explored the task of reconstruction can hardly be begun. In that work of exploration all classes of naturalists will alike find interest. The methods are definite and exact, so we need not fear the alienation of those systematists to whom all theoretical inquiry is repulsive. They are also wide in their scope, and those who would turn from the details of classification as offering matter too trivial for their attention may engage in genetic inquiries with great confidence that every fragment of solid evidence thus discovered will quickly take its place in the development of a coordinated structure.

Some pre-Mendelian Writings.

Of the contributions made during the essayist period three call for notice: Weismann deserves mention for his useful work in asking for the proof that “acquired characters”—or, to speak more precisely, parental experience—can really be transmitted to the offspring. The occurrence of progressive adaptation by transmission of the effects of use had seemed so natural to Darwin and his contemporaries that no proof of the physiological reality of the phenomenon was thought necessary. Weismann’s challenge revealed the utter inadequacy of the evidence on which these beliefs were based. There are doubtless isolated observations which may be interpreted as favouring the belief in these transmissions, but such meagre indications as exist are by general consent admitted to be too slight to be of much assistance in the attempt to understand how the more complex adaptative mechanisms arose. Nevertheless it was for the purpose of elucidating them that the appeal to inherited experience was made. Weismann’s contribution, though negative, has greatly simplified the practical investigation of genetic problems.

Though it a...

Table of contents

• Title Page
• Copyright Page
• PREFACE
• Table of Contents
• Table of Figures
• PART I
• PART II
• BIBLIOGRAPHY
• INDEX OF SUBJECTS
• INDEX OF AUTHORS