In the phenomena of unisexual generation we see that the larger organisms never reproduce themselves in the unisexual way, while the smaller organisms reproduce themselves with the greatest rapidity by this method. Between these two extremes unisexual reproduction decreases while the size increases. In the history of all plants and animals is evident the physiologic truth, that while the general growth of the individual proceeds rapidly, the reproductive organs remain imperfectly developed and inactive. On the contrary, the principle of reproduction indicates decrease in the intensity of growth and becomes a cause of cessation.
Great fecundity is always attended by great mortality. Each superior degree of organic evolution is accompanied by an inferior degree of fecundity. The greater the germs the less is the individuation, and vice versâ. The greater and more complex the organisation, the less is the power of multiplication.
What is true of the cells is also true of organs composed of them. Each organ can be regarded as a distinct animal (a parasite is preferable for comparison) which has its own nervous system (the ganglia), but is fed and controlled by the organism as a whole. Degeneration of this organ may therefore be an expression of a local state peculiar to it and either beneficial or maleficent, or both in inverse degree, to the organism as a whole, or it may be the expression of a general defect in the whole organism. The sclerotic states of the appendix vermiformis in man and of the human liver are, as Kiernan has shown, two excellent illustrations of the degeneracies last described. Man, in common with the four anthropoid apes, has a little thin tube attached to the cæcum known as the appendix vermiformis. In the early embryo it is equal in calibre to the other bowels, but ceases to grow proportionately after a certain time. In the new-born child it is almost as large as in the adult. As this tube proved disadvantageous to man’s precursor (as it does to certain mammals) from catching foreign bodies which form the nucleus of enteroliths or bowel stones, it has lost the nutritive supply of the other intestines and is tending to disappear. It is often absent in man. The defect in its structure, while predisposing to the attacks of germs and an expression of its own degeneracy, is an evidence of an advance in evolution in the organism as a whole by which great danger and waste of nutritive force are avoided.
Recent researches[60] have shown that “hob-nail” liver, once supposed to be due entirely to abuse of alcohol, usually occurs in states of congenital deficiency in persons of defective heredity. The change in the appendix which is tending to cause its disappearance is essentially a sclerosis, and hence is morbid, considered from the appendix standpoint alone. As the same process occurs in “hob-nail” liver, it is obvious that degeneracy may be an expression of general advance and local defect or may be a local expression of general defect. The same phenomenon is seen in the nervous system. The researches of Cunningham[61] have shown that in man the struggle for existence between the sympathetic and the cerebro-spinal system has ended in the victory of the latter, while the first is tending to disappear. Such changes must necessarily result in local degeneracies which are for the benefit of the organism as a whole. Degeneracy on this basis may express itself in simple disturbance of the lower or nutritive functions. The uric acid or gouty states, for example, are, as Fothergill long ago pointed out, assumptions by mammalian organs of the functions of those of birds and reptiles. In conditions like myxœdema the skin, through thyroid gland disturbances, takes on features which resemble in result those found in certain mollusks and low fish. These nutritive disturbances may show themselves in disorders of the pituitary body (acromegaly, giantism, &c.), whereby the bony system of man reverts to conditions like those of the gorilla. The same conditions also appear in the diathesis of the “bleeders.” All these conditions, however, may be an expression of a degenerate type assuming a normal equilibrium, as well as of a normal organism taking the first steps in degeneracy.
In a general way, therefore, as Dohrn has pointed out, this principle holds good of man not only as an organic unit but as a compound organism. Degeneracy[62] is a gradual change of structures by which the organism becomes adapted to less varied and less complex conditions of life. The opposite progression process of elaboration is a gradual change of structure in which the organism becomes adapted to more and more varied and complex conditions of existence. In elaboration there is a new expression of form corresponding to new perfection of work in the animal machine. In degeneracy there is suppression of form corresponding to the cessation of work. Elaboration of some one organ may be a necessary accompaniment of degeneracy in all the others. This is very generally the case. Only when the total result of the elaboration of some organs, and the degeneracy of others, is such as to leave the whole mass in a lower condition—that is, fitted to less complex action and reaction in regard to its surroundings than is the type—can the individual be regarded as an instance of degeneracy. These degeneracies appear at varying periods, since struggles for existence on the part of the different organs and systems of the body are most ardent during periods of body evolution and involution. During fœtal life, during the first dentition, during the second dentition (often as late as the thirteenth year), during puberty and adolescence (fourteen to twenty-five), during the climacteric (forty to sixty), when uterine involution occurs in woman and prostatic involution in man, and finally during senility (sixty and upwards), during all these periods degeneracy may be shown by mental or physical defect, a congenital tendency to which has remained latent until the period of stress. These defects may be such biochemic alterations (undemonstrable by existing methods) as lead to diminished inhibitory power or other altered function, or to secondary pathologic or teratologic change of decidedly demonstrable nature. Organs and structures checked at a certain phase of development may pursue a course of development differing from that pointed out in man but outlined in other vertebrates. The human cyclopean monstrosities, for example, might be regarded as reversions to the single-eyed sea-squirts, who are possibly the Ascidian precursors of the vertebrates.
The scope of degeneracy may therefore be limited to certain signs which are its sole expressions. These signs (stigmata as they were early called) may be the only expression of degeneracy, and their significance must be determined by a careful examination of the organism in which these expressions are found, since they may be merely defects produced by degeneracy, or may indicate how deep such degeneracy has penetrated. They may, therefore, indicate either slight or serious defect. In proportion to the depth of degeneracy in the organism will the stigmata affect the earlier simpler or later complicated acquisitions through evolution. Of necessity, when the organism is affected by degeneracy, the morbid element will take the line of least resistance, determined by the depth of degeneracy as well as the variability of the structures concerned. The same influence must equally affect functions of the structures. Furthermore, expressions of degeneracy will, as already stated, be influenced by the periods of stress; the first and second dentition, puberty, the climacteric and the senile period. In a general way these stigmata are divisible into mental and physical, and are best observable in their relations to the periods of stress. In certain races, as in certain animals, conditions appearing before puberty was completed cannot be considered as settling the position of the animal in evolution. What is true of individuals is also true of classes. The anthropoid apes and the negroes are much higher in physical characteristics, with potential mental results, before puberty than after. The infant ape, as Havelock Ellis[63] points out, is very much nearer to man than the adult ape. “The infant ape is higher in the line of evolution than the adult, and the female ape, by approximating to the infant type, is somewhat higher than the male. Man, in carrying on the line of evolution, started not from some adult male simian, but from the infant ape and, in a less degree, from the female ape. The human infant bears precisely the same relation to his species as the simian infant bears to his, and we are bound to conclude that his relation to the future evolution of the race is similar. The human infant presents, in an exaggerated form, the chief distinctive characteristics of humanity—the large head and brain, the small face, the hairlessness, the delicate bony system. By some strange confusion of thought we usually ignore this fact, and assume that the adult form is more highly developed than the infantile form. From the point of view of adaptation to the environment, it is undoubtedly true that the coarse, hairy, large-boned and small-brained gorilla is better fitted to make his way in the world than his delicate offspring; but from a zoological point of view we witness anything but progress. In man, from about the third year onwards, further growth—though an absolutely necessary adaptation to the environment—is to some extent growth in degeneration and senility. It is not carried to so low a degree as in the apes, although by it man is to some extent brought nearer to the apes, and among the higher human races the progress towards senility is less marked than among the lower human races. The child of many African races is scarcely, if at all, less intelligent than the European child, but while the African as he grows up becomes stupid and obtuse, and his whole social life falls into a state of hide-bound routine, the European retains much of his childlike vivacity. And if we turn to what we are accustomed to regard as the highest human types, as represented in men of genius, we shall find a striking approximation to the child type.” The face, in its contest for existence with the brain, has finally caused both the cranium and the jaws to assume (for defence and food purposes) a lower type, although as regards existing functions and the higher standpoint of environment the infantile type must be considered the higher. Still a casual glance at the Ascidian tadpole shows that deficient as is the development of the ganglia afterward forming the medulla, the face is still more deficient. The face, as Minot shows,[64] is a characteristic of the higher vertebrates, and acquires increased importance with rise in the evolution. The position of the face in embryonic development is originally determined by the head-bend. If a median, longitudinal section of the head be imagined to occupy a rectangular area divided into quarters, then the lower posterior quarter corresponds to the mouth region, the other three-quarters to the brain. As development progresses, the mouth quarter so disproportionately enlarges in relation to the rest of the head as to project forward in front of the fore-brain. In this stage, which is represented by the adult amphibians, the bulk of the facial apparatus is very great, proportionately to the cranium. In the reptiles the mouth region is elongated still further in front of the brain-case, resulting in the long snout. In mammals a third stage is established by the great increase in size of the brain, especially of the cerebral hemispheres. In consequence the brain comes to extend over the snout, as it were; in man, whose brain has the maximum enlargement, the facial apparatus is almost entirely covered by the brain. In the course of evolution the face, while serviceable to the animal for certain reasons of general constitutional character (food-getting, means of defence and means of obtaining mates), is less so than brain growth. A struggle for existence, therefore, inevitably results between the tendency of the face to appropriate power of growth and the like tendency of the brain, which, in defective organisms, produces marked reversions of the one for the benefit of the other. This struggle is further complicated by the embryonic relations to both of the hypophysis, since this body admittedly exerts an influence over bone growth, most markedly (but abnormally) exhibited in acromegaly (excessive bone growth). In this contest for existence in the degenerate types, degeneracy will, of necessity, take the direction of least resistance. As the brain is the last acquirement in vertebrates, considered from the standpoint of necessity, while the face (also a late acquirement) is much less complex, the last, obviously, will present the derangements from degeneration in shape, while the former will show these in shape and function. Furthermore, during the embryonic period the development of the brain will, of necessity, be more immediately affected by degeneracy than the face, which will gain in evolution at its expense. The stigmata of degeneracy, therefore, most likely to attract attention are in the order given, those of the face, jaws, and teeth; ear, eye, cranium; body, bodily functions; brain and spinal cord. Under these last are to be included their mental and nervous functions.
The following table summarizes in practical form these stigmata[65]:—
The factors producing degeneration act by causing nervous exhaustion in the first generation. This implies a practical degeneration in function since tone is lost.
Every nerve cell has two functions, one connected with sensation or motion, and the other with growth. If the cell be tired by excessive work along the line of sensation or motion the function as regards growth becomes later impaired, and it not only ceases to continue in strength, but becomes self-poisoned. Each of the organs (heart, liver, kidneys, &c.) has its own system of nerves (the sympathetic ganglia), which while under control by the spinal cord and brain act independently. If these nerves become tired the organ fails to perform its function, the general system becomes both poisoned and ill-fed, and nervous exhaustion results. In most cases, however, the brain and spinal cord are first exhausted. The nerves of the organs are thus allowed too free play, and exhaust themselves later. This systemic exhaustion has local expression in the testicles in the male, in the womb and ovaries in the female. Through this the body is imperfectly supplied with natural tonics (antitoxins) formed by the structures, and the general nervous exhaustion becomes still more complete. All the organs of the body are weakened in their function. Practically the neurasthenic in regard to his organs has taken on a degenerative function albeit not degenerating in structure, since the restlessness of the organs is a return to the undue expenditure of force which occurs in the lower animals in proportion as it is unchecked by a central nervous system. Through the influence of various exhausting agencies the spinal cord and the brain lose the gains of evolution and the neurasthenic is no longer adjusted to environment. Since the reproductive organs suffer particularly, children born after the acquirement of nervous exhaustion, more or less checked in development as the influence of atavism is healthy or not, repeat degenerations in the structure of their organs, which in the parent were represented by neurasthenic disorders in function. As the ovaries of the neurasthenic women generally exhibit prominently the effects of the nervous exhaustion, the offspring of these do not retain enough vigour to pass through the normal process of development.