Heredity and selection in sociology

Front matter

I k

Hv -

HEKEDITY AND SELECTION IN SOCIOLOGY

Part I The Theory Of Descent

The Factors op Evolution

Importance of Darwin’s work for biology and sociology — The four factors at the basis of the theory of descent — Variability, heredity, excessive fecundity, selection — Struggle for existence, indirect as well as direct — Importance of conflict — Three degrees in the biological value of progeny .... 1-10

The Mechanism of Heredity

1. The two great groups of organic beings, unicellulars and multi-

cellulars — Intermediary forms — Growth of the division of labour : reproductive and somatic cells ; sexual differentiation.

2. Experiments of Hertwig on the egg of the sea - urchin —

Mechanism of fecundation — Cellular division, or karyokinesis — Highly complex nature of cellular nucleus — Fundamental importance of the chromosomes — Result of karyokinesis : equal division of chromatic substance, and equal repartition of the chromosomes between the two daughter-cells — The germ-plasm —

Equal biogenetic value of nucleus in the egg and in the spermatozoon : experiment of Boveri — Conjugation of Noctiluca — Maturation of the germ-cells — Role of the chromosomes during the process of maturation— Amphimixis — Adaptation of the egg and the spermatozoon to amphimixis — The meaning of amphimixis — Experiments of Maupas on infusorians — Experiments of Weismann on Cypris reptans — Regression of centro-

vii

V1U some in matured egg — This regression can be prevented by artificial means — Experiments of Tichomiroff, Loeb, and Petrunkewitsch.

3. Weismann’s theory of the germ-plasm — The continuity of the germ-plasm— Active and inactive germ-plasm — Active germ-plasm is adapted to the needs of the ontogeny, inactive germ-plasm to the needs of the phylogeny — The germ-plasm is located in the chromosomes — Structure of the germ-plasm : ids, determinants, biophors — The “ germinal tract ” — Function of the determinants — Homodynamic and heterodynamic determinants—Integral and differential division of the determinants — Active and passive determinants — Liberation of determinants during the embryogenesis — Vital affinities — Histological determination of the cell — Struggle of the parts within the organism ; theory of Wilhelm Roux — The number of determinants — Summing-up 11

CHAPTER III Germinal Selection

1. Preformation of the organism in the germ — Heterogeneity of the

germ-plasm — The determinants are autonomous living particles in definite developmental relation to given parts of the finished organism — The modification of the determinants entails corresponding modification of these parts.

2. Germinal selection — Force of the objections formerly raised

against the original theory of the ancestral plasm — These objections now answered by the theory of germinal selection — The original source of variations — Elementary particles of the germ-plasm demand and receive nourishment — The biophors are capable of assimilation and growth — The strength of the determinants depends on the available quantity of nourishment, and on the assimilatory capacity of the determinants — Amphimixis mingles the heterogeneous ids — Quantitative and qualitative differences increase in proportion to the number of determinants— Heterogeneous determinants and the influence exercised by homogeneous environing conditions — Regression of the determinants — Source of all hereditary variation to be found in shiftings of the balance among the determinants — Action of natural selection on germinal variations — Limitation of ascendant variations — Illimited character of regressive variations — Regression of useless organs — Role of amphimixis in germinal selection— The reducing divisions and germinal selection — Correlation

IX 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 faculty— Correlation of psychical faculties in genius — All the changes in the germ-plasm are quantitative in their nature - - 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-Sequard — Unsatisfactory character of these experiments — A general pathological condition is transmitted, not the disease itself.

2. The case of instinct — Instinct as “inherited habit” — Refu-

tation 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

X

CHAPTER V Instinct

Useful morphological characters due to natural selection — Correlation between morphological and psychological characters — Centralisation 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 — Correlation of colour and instinct in Xylina — The instinct of conjugation among micro-organisms — Consciousness is at the origin of complicated series of actions adapted to a definite end — Nevertheless, instinct is not always the result of conscious volition — Example of Sitaris humerales — Instinct of the sea-cucumber, Cucumaria 85-95

Chapter VI

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 — Symmetrical and asymmetrical curves— In symmetrical curves constancy 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 — Summary 96-108

CHAPTER VII Consanguinity

Although continual mingling of heterogeneous germ-plasms be advantageous for the species, consanguinity is not necessarily harmful — Biological results of exogamous and endogamous pairing — Reasons of consanguineous degeneracy — Consanguineous degeneracy presupposes unfavourable variations, but

XI the latter are not produced by consanguinity — Difference between parthenogenesis and consanguinity— Hermaphroditism — Mode of reproduction in each case an adaptation to the conditions of life — Heterogeny of the Daphnids — Development of exogamous and endogamous institutions in the human species — Remarkable case of human consanguinity — Consanguinity among other animal species ------ 109-119

CHAPTER VIII Hybridism and Intercrossing

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 crossing of variations — Degeneracy of human hybrid races - 120-128

CHAPTER IX The Origin and Extinction of Species

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 Nageli — Insufficiency of the theory of Nageli — 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 Nageli and Darwin.

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 modifications 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 Nageli on Hieracium— Influence of temperature on the pupa — Experiments of Weismann on Polyommatus 'phlceas — Experiments of Standfuss and Merrifield on Vanessa — Aberrations caused by the influence of temperature are in a certain degree hereditary — The limits of adaptation.

Xll

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 always due to changes in the environing conditions - - 129-156

CHAPTER X Parents and Offspring

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-complexes 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 — Preponderance of homodynamic over heterodynamic determinants — Specific determinants of the species always homodynamic — Large number of individual variations rendered possible by neotaxis of the germ-plasm — Number of variations dependent on the number of chromosomes 157-164

Appendices 165-173