SUMMARY OF CHAPTERS between the utility of a variation and its production-The luminous apparatus of deep-sea fishes. 3. Co-operation between natural selection and germinal selection -Germinal selection effectuates variations of morphological value, natural selection effectuates variations of biological value -Fore-wing of Phyllodes ornata-Tendency of the determinants to vary-Nevertheless, many species remain constant during long periods-The reason of this constancy is to be sought for in the inhibitory action of natural selection, which regulates the force of the variations in the germ-plasm-Only variations of morphological value are controllable by germinal selection-Plus-variations in one group of determinants entail minus-variations in other groups-Mutations-No antithesis between constancy and adaptability-Specific psychical talents-The musical facultyCorrelation of psychical faculties in genius-All the changes in the germ-plasm are quantitative in their nature CHAPTER IV ix PAGES 41-64 THE LAMARCKIAN HYPOTHESIS OF THE INHERITANCE OF ACQUIRED CHARACTERS 1. Contradiction between the theory of Weismann and that of Lamarck-Untenability of the Lamarckian hypothesis-The results of mutilation-Experiments of Weismann-Inborn mutilations different to acquired mutilations-Adverse evidence of cattle-breeders-Acquired and transmissible diseases-Disease can affect the germ-plasm as much as the soma-Syphilis and alcoholism - Tuberculosis is transmitted indirectly, not directly-Cancer not hereditary-The alleged transmission of epilepsy-Experiments of Brown-Séquard - Unsatisfactory character of these experiments-A general pathological condition is transmitted, not the disease itself. 2. The case of instinct-Instinct as "inherited habit "- Refutation of this conception of instinct-Instincts which manifest themselves but once in a lifetime-Natural selection suffices to explain the phenomenon of instinct—An act of volition can become instinctive-Instinct can occasionally be the result of tradition-Modification of the passive parts of the organism— Regression of the wings and ovaries of worker-ants-The biogenetic law-Harmony between the biogenetic law and the determinant theory-Co-adaptation-The horns of the Irish stag -Useful variations not only possible, but necessary-Formation of the membranes of insects 65-84 CHAPTER V INSTINCT Useful morphological characters due to natural selection-Correlation between morphological and psychological characters-Centralisa- tion of the nervous system necessary to the development of consciousness-Ribot on instinct as an inherited habit ". Impossibility of accepting consciousness as the basis of instinct among primitive organisms-Reflex action-Instinct a succession of reflex combinations-Instinctive movement the result of the action of external stimuli on certain cerebral centres-Correla- tion of colour and instinct in Xylina-The instinct of conjugation among micro-organisms-Consciousness is at the origin of com- plicated series of actions adapted to a definite end-Neverthe- less, instinct is not always the result of conscious volition- PAGES THE BIOLOGICAL IMPORTANCE OF AMPHIMIXIS Correlation between the age of an organic character and its persistence -Amphimixis does not necessarily entail multiplication or rejuvenation-Persistence of amphimixis due to the stability of the determinants of this character-Natural selection causes the maintenance of amphimixis-Amphimixis a necessary check on excessive variation-Adaptation assured by amphimixis-Sym- metrical and asymmetrical curves-In symmetrical curves con- stancy is identified with normality-In asymmetrical curves constancy is separated from normality-Causes of asymmetrical curves-No antithesis between constancy and adaptation- Amphimixis ensures constancy and adaptability-Simultaneous regressive variation of useless organs rendered possible by amphimixis-Minute adaptation of conjugating cells to each other Although continual mingling of heterogeneous germ-plasms be the latter are not produced by consanguinity-Difference between parthenogenesis and consanguinity-Hermaphroditism -Mode of reproduction in each case an adaptation to the con- ditions of life-Heterogeny of the Daphnids-Development of exogamous and endogamous institutions in the human species Quatrefages on the social value of intercrossing-Adverse opinion of Gobineau-Hybridism and intercrossing beyond the limits of the species-Sterility of hybrids-Influence of domestication on the fertility of hybrids-Degrees of fertility among hybrids- Causes of sterility among hybrids-Crossing of distinct species and 1. Variation, selection, and heredity the three principal factors in the evolution of species-The land-snakes of the Celebes-Spatial evolution Species are complexes of adaptation-The " phyletic force" of Nägeli-Insufficiency of the theory of Nägeli-The mutations theory of De Vries-Difficulty of ascertaining the biological value of a part-The shell of the Celebes land-snails -Secondary characters determined by germinal selection- Primary characters determined by natural selection completing germinal selection-Reconciliation of the theories of Nägeli and 2. Biologically indifferent variations as characteristics of a species -Such variations can be produced by the action of the environment-The alleged hereditary transmission of modifica- tions acquired under the influence of environing conditions- The case of galls on plants-Modifications effected by the action of the environment which remain purely somatic-Important modifications of the soma are not transmitted-Experiments of Nägeli on Hieracium-Influence of temperature on the pupa- Experiments of Weismann on Polyommatus phlaas-Experi- ments of Standfuss and Merrifield on Vanessa-Aberrations caused by the influence of temperature are in a certain degree 3. Importance of isolation in the evolution of species - How isolation effects the development of variations-Co-operation of isolation and natural selection-Amixis does not necessarily produce variation-The sexual "isolation" of Romanes. 4. The action of selection on the origin of species-The life- history of species-Death not a necessity inherent to organic life-Immortality of the Protozoa and of the germ-plasm of the Metazoa-No parallel between ontogeny and phylogeny- Death not a constitutional necessity for species-Extinction of species is due to inability to effect sufficiently rapid readaptation -Case of the Trilobites-Extinction may also result from direct inferiority-Extinction of inferior human races-Extinction is 129-156 Elimination of ancestral ids from the germ-plasm by the expulsion of the polar bodies from the egg, and the repeated division of the sperm-cell before maturation-Persistence of former id-com- plexes in the human germ-plasm-Significance of the reducing divisions for the theory of descent-Multiplication of variations by amphimixis-Distinctness of male and female elements in the nucleus of fertilised ovum throughout the embryogeny-Pre- ponderance of homodynamic over heterodynamic determinants -Specific determinants of the species always homodynamic- Large number of individual variations rendered possible by neo- APPENDICES 157-164 1. Innate tendency of organic life counteracted by the action of SUMMARY OF CHAPTERS determining factor of suicide-Suicide among the religious de- 2. The majority of the wants of civilised man are not of a 4. Conflict is not a determining cause of social disintegration— This disintegration is due to excessive individualism-Destruction of the successive principles which have ensured the integration of the various social types-Growth and extension of the State-Necessity for the re-establishment of a principle ensuring social integration xiii PAGES 177-252 1. Increase in the rate of insanity an alarming symptom of our social life-Although it be true that all movement, whether physiological or social, implies loss; nevertheless excessive loss occasions a serious weakening of vital force-Selection eliminates the weak and the degenerate; insufficiency of the action of selection in our social life to-day-The fact that the increase in the rate of suicide does not in itself imply an increase in the rate of insanity must not be taken as denying the reality of such an increase of insanity-The individual element appears more clearly in considering insanity than it does in considering suicide, for suicide is not bound up with any clinical form of mental aberration-Social causes are, however, in a large measure responsible for the increase in the insanity-rate. 2. Statistics relating to the increase of insanity in general, of alcoholic insanity, and of general paralysis-Statistics relating |