PART I
INTRODUCTORY

1. HOMEOSTASIS

ONE of the most important contributions made by Walter B. Cannon to the field of physiology was the development and elaboration of the concept of physiological homeostatis. He has defined homeostasis as the totality of steady states maintained in an organism through the co-ordination of its complex physiological processes. By extension it may be said that homeostasis refers to the property of the organism to adjust itself to variable conditions, or to the self-regulatory mechanisms of the organism which permit it to stabilize itself in fluctuating inner and outer environments.

The idea of balance as a necessary condition for the preservation and perpetuation of life is an ancient one, and has been traced by Cannon, at least in its primitive form, to the time of Hippocrates. Undoubtedly, the early notions on the subject tended to view homeostatic mechanisms from a crude vitalistic standpoint. It is to the richly deserved credit of Cannon and his followers that this apparently mysterious and mystical property of biological organisms has been reduced to terms of interactions between constituent parts and functions. Needless to say, final answers to the problems of physiological homeostasis are by no means available. Indeed, the origin of biological feedback mechanisms is in itself a question of central interest in the study of evolution. Their existence is recognized, the largely mechanistic basis of their operation is accepted, but their increasingly complex development from the lower to the higher forms of life still presents the focal problem of evolution of adaptations. That physiological homeostasis is essentially the fundamental adaptation was recognized even before the term was coined, for, as Claude Bernard (quoted from Haldane, 1932) stated three-quarters of a century ago, 'all the vital mechanisms, varied as they are, have only one object, that of preserving constant the conditions of life in the internal environment'.

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Genetic Homeostasis
Table of contents

Table of contents

  • Title Page iii
  • Acknowledgments. v
  • Contents vii
  • Part I - Introductory 1
  • 2. the General Hypothesis 4
  • Part II - Evidence 8
  • 5. Selective Advantage of Heterozygotes 13
  • 6. Inbreeding Degeneration 22
  • 8. Wing Venation in Drosophila 27
  • 9. Other Phenodeviants 34
  • 10. Variability of Heterozygotes 38
  • 11. Variance of Heterozygotes in Drosophila 50
  • Part III - Interpretation 63
  • 16. Relict Homeostatic Traits 72
  • 17. Model of Genetic Homeostasis 79
  • 18. Genetic Homeostasis and Selection 81
  • 19. Stabilizing Selection 95
  • 20. Evolution of Buffering Properties 99
  • Bibliography 121
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