Twins : Heredity and Environment

THE study of twins is equally interesting to the layman and to the scientist. This is a happy circumstance, for there are few media offering so excellent an approach to the problems of heredity and environment as is afforded by the scientific investigation of twins. In view of the universal interest in twins the author has attempted to present the following study in as non-technical a form and style as possible, in the hope that the study may reach some small part of the educated public as well as the specialist.To essay to write for two types of readers is a hazardous task, but it seems to the author that the vital need of presenting all possible knowledge of the complicated interrelationships of heredity and environment in human affairs to as large a number of intelligent persons as possible makes apologies superfluous. Yet he is constantly mindful that in writing for the two types at the same time he resembles the tight-rope walker learning to combine his feat with juggling. The writer is indebted to Professor Ε. M. East for a number of constructive criticisms, for his calling attention to several unusual cases of twins, and for his sympathetic interest in the study. The experiment was supervised by Professor William McDougall, to whom the writer is indebted both for his counsel and for his suggestions. The writer owes many sincere thanks to the hundred or more school-teachers and settlement-house workers and directors for their generous cooperation in many ways. Lastly the author is indebted to his colleague Dr. Elizabeth M. Hincks for the reading of the proof. ACKNOWLEDGMENTS CONTENTS CHAPTER I. INTRODUCTION CHAPTER II. MONSTROSITIES AND TWINS CHAPTER III. SUNDRY FACTS CONCERNING TWINS CHAPTER IV. A REVIEW OF SOME EXPERIMENTAL STUDIES UPON TWINS CHAPTER V. OUR EXPERIMENTAL APPROACH AS RELATING TO HEREDITY AND ENVIRONMENT: METHODS, TESTS, PROBLEMS CHAPTER VI. DATA ON DISSIMILAR TWINS LIVING IN SIMILAR ENVIRONMENT CHAPTER VII. DATA ON SIMILAR TWINS LIVING IN SIMILAR ENVIRONMENT CHAPTER VIII. DATA ON SIMILAR TWINS LIVING IN DISSIMILAR ENVIRONMENTS CHAPTER IX. RESULTS: THEIR INTERPRETATION AND IMPLICATIONS CHAPTER X. CONCLUSIONS INDEX