WeRead Powered by ReaderPub
Essays Upon Heredity and Kindred Biological Problems / Authorised Translation cover

Essays Upon Heredity and Kindred Biological Problems / Authorised Translation

Chapter 43: APPENDICES.
By August Weismann
Open in WeRead

Explore more books like this:

Science - Biology

About This Book

A collection of linked essays examining biological inheritance and related problems. It opens with an inquiry into factors that determine organismal lifespan and then develops a theory of heredity centered on the continuity of the germ-plasm. Subsequent essays analyze the significance of sexual reproduction, the number and role of polar bodies, and the conditions that allow parthenogenetic development. Other pieces critically evaluate botanical and experimental claims for the transmission of acquired characters and for the heritability of mutilations. Empirical observations are combined with theoretical interpretation, and the essays are presented as successive stages in a progressively refined research program.

SIGNIFICANCE OF SEXUAL REPRODUCTION, etc.

CONTENTS.

PAGE
1. Can we dispense with the principle of natural selection? 255
2. Nägeli’s theory of transformation from internal causes 256
3. A definite course of development is possible without a self-changing idioplasm 258
4. Conclusive importance of ‘adaptations’ 260
5. The structure of whales as an example of adaptation 261
6. Transformation takes place by the smallest steps 264
7. The foundation of such minute changes depends upon individual variability 266
8. Difficulty in accounting for variability on the supposition of a continuity of the germ-plasm 266
9. Previous theories by which variability has been accounted for 267
10. Non-transmission of acquired characters 267
11. Nägeli’s and Alexis Jordan’s experiments 269
12. Germ-plasm is only altered with great difficulty 271
13. The source of individual variation lies in sexual reproduction 272
14. The process of natural selection does not operate when asexual reproduction takes place 274
15. Origin of variability in unicellular organisms 278
16. Sexual reproduction effects combination 279
17. E. van Beneden’s and V. Hensen’s theory of sexual reproduction as a process of rejuvenescence 282
18. Theoretical objections to such a view 283
19. Original significance of conjugation 286
20. Preservation of sexual reproduction by means of heredity 287
21. It is lost in parthenogenesis for reasons of utility 289
22. Parthenogenesis prevents further transformations 290
23. It excludes Panmixia and thus prevents disused organs from becoming rudimentary 291
24. Final considerations 294

APPENDICES.

I. Further considerations which oppose Nägeli’s explanation of Transformation as due to internal causes 298
II. Nägeli’s Explanation of Adaptation 300
III. Adaptations in Plants 308
IV. On the Supposed Transmission of Acquired Characters 310
1. Brown-Séquard’s experiments on Guinea-pigs 310
2. A case which at first sight appears to prove the transmission of acquired characters 320
V. On the Origin of Parthenogenesis 323
VI. W. K. Brooks’ Theory of Heredity 326