Reproductive instinct

“ We think, for example, that birds pair for the sake of mere sexual gratification; why, then, do they leave off pairing as soon as they have laid the requisite number of eggs? That there is a reproductive instinct over and above the desire for sexual gratification appears from the fact that if a man takes an egg out of the nest, the birds will come together again and the hen will lay another egg; or, if they belong to some of the more wary species, they will desert their nest, and make preparation for an entirely new brood. ”

“ Moreover, the instincts connected with sexual union and with offspring are separate and distinct. In popular, confused thought, a reproductive 107instinct is attributed to animals and man. In reality, no direct instinct to reproduce the species exists. Animals unite sexually from an instinct directed to a pleasurable exercise of function; and although, in man, the relation has been made complex by his knowledge of the facts of reproduction and of social life, the sexual instinct is connected solely with pleasure and social feeling—not with reproduction. ”

“ Having once originated, the sexual type of reproduction possessed a definite survival value which assured its continuation. Sex makes possible a crossing of strains, which evidently possesses some great advantage, since the few simple forms which have no such division of reproductive functions have undergone no great development and all the higher, more complicated animals are sexual. ”

“ I have remarked in the first chapter—but a long catalogue of facts which cannot be here given would be necessary to show the truth of the remark—that the reproductive system is eminently susceptible to changes in the conditions of life; and to this system being functionally disturbed in the parents, I chiefly attribute the varying or plastic condition of the offspring. The male and female sexual elements seem to be affected before that union takes place which is to form a new being. ”

“ Darwin has shown that changed conditions of life have an especial power of acting injuriously on the reproductive system. Thus animals, as also plants, when removed from their natural conditions, are often rendered in some degree infertile or completely barren, even when the conditions have not been greatly changed. ”

“ It is an interesting physiological fact that, while the growth and development of the individual are rapidly progressing, the reproductive powers remain almost inactive, and that the commencement of reproduction not only indicates an arrest of growth, but, in a great measure, contributes toward it. ”

“ In such cases the physiological difference between the sperm-producer and the ovum-producer, for this is the essential difference, saturates through the body and expresses itself in masculine and feminine structures and modes of behaviour. The expression of the masculine and feminine characters is in some cases under the control of hormones or chemical messengers which are carried by the blood from the reproductive organs throughout the body, and pull the trigger which brings about the development of an antler or a wattle or a decorative plume or a capacity for vocal and saltatory display. ”

“ The prolonged dependence of the child upon the care of its parents is calculated to abate the fervor and force of reproductive inclination.
While in man the reproductive act is not the precursor of death, yet it is the premonition of that event and the instinctive effort which nature makes to prevent the extermination of the race. ”

“ In the simplest forms of conjugation the functions of both parents appear to be identical, but in organisms which are a little more specialized we find male and female reproductive bodies, and the offspring is the result of the union of the male element of one individual with the female element of another; that is, we have true sexual reproduction in its simplest form. ”

“ After the act of procreation, the sexual passion in both subsides, and the reproductive function is not again called into exercise until after the intervening weeks or months of repose have passed and nature again responds to the necessity of procreation for the purpose of perpetuating the species. Where the periods of ovulation and fecundity recur at brief intervals in the female, the reproductive nature of the male is in a more continuous state of activity, so that a fruitful union may be secured when the reproductive nature of the female is in readiness ”

“ Now, as we have already seen, much modern biological discussion centres round the question whether the detached reproductive fragment, ovum or sperm as the case may be, is derived from the whole body of the parent, by what Darwin termed pangenesis or in some other way, or only from germinal substance set apart in development for this end. ”

“ The last step in generation is reached in the mammals. Here not only fertilization is accomplished within the body of the female, but also the entire development of the fertilized125 ovum is carried out in the uterus, inside the female body. Hence mammals give birth to living mature young.
In these higher animals the attraction of the sex cells has been definitely transferred to, or rather changed into, the attraction of the hosts of these cells or into the sexual instinct. ”

“ The principle of construction and operation of the reproductive system, by which an individual animal is produced from an egg brought forth by the female parent, and is thereafter nourished without anything derived from the parental body, is as widely different from that by which the young animal is born from a womb and nourished for a time from the milk of the mother, as any two constructions, animate or inanimate, that can be conceived of. ”

“ II. That sex is determined in the moment of fertilization by the reciprocal interaction of male and female, of zoösperm and ovum. One variant of this theory maintains that each reproductive element strives for the reproduction of its own sex; that a struggle takes place and that the victor in the contest stamps its own sex-likeness upon the fertilized product. ”

“ The above general statements respecting the division and correspondence of the sexual organs in the male and female, and their connection with the brain through the nervous system, are true of all the Mammalia, where, as in man, the reproductive power exists in two separate individuals. When, however, we consider the way in which these functions act in the work of reproduction, an important difference is observed between their action in man and in the lower animals. This difference places man physically in a different and superior category from the brute creation. ”

“ But there is no difficulty in believing that the sexual elements of each differ slightly in the same diversified manner as do their external characters; and it has often been remarked that no two individuals are absolutely alike. Therefore we can hardly avoid the conclusion, that differences of an analogous and indefinite nature in the reproductive system are sufficient to excite the mutual action of the sexual elements, and that unless there be such differentiation fertility fails. ”

“ Credible observations even exist, indicating that among many primitive peoples, in whom at the time of puberty no social laws hinder the limitless exercise of the reproductive functions, this capacity on the part of woman to conceive at any time has no existence, and that the reproductive capacity of such human beings is, like that of the lower animals, confined to a certain season of the year. ”

“ This theory, of course, implies variation in the reproductive organs, or departure from the parental type, in at least two individuals of opposite sex simultaneously, and with this admission, for which we are justified in facts, physiological selection will preserve many peculiarities which need have no necessary connection with the exigencies of life. ”

“ It will suffice for our purpose to assume that they are now mature. Then as the result of a natural instinct which suggests certain thoughts and emotions to the male and female animals, which in turn are followed by certain definite acts, the sperm-cell from the male and the egg or ovum-cell from the female are brought into contact. ”

“ But before closing this chapter upon the complemental differences between the two sexes, it will be interesting to observe some remarkable similarities in the reproductive organs themselves, and to note how, in that infinite wisdom which is marvelous in our eyes, God has so modified their form and office that the external organs of reproduction in man become the internal and seemingly different organs of reproduction in woman. ”

“ We must not overlook the effects of the unequal combination of the characters derived from both parents, nor reversion to former progenitors. Changed conditions have an especial tendency to render the reproductive organs more or less impotent, as shown in the chapter devoted to this subject; and these organs consequently often fail to transmit faithfully the parental characters. ”

“ And so, when we come to consider the question of reproduction in the higher forms of life, we are apt to focus attention too much upon the sexual function and too little upon the contributory factors, the failure of any one of which would mean failure of the whole. ”

“ In all the different forms of a-sexual reproduction, from fission to parthenogenesis, the female may in this sense be said to exist alone and perform all the functions of life, including reproduction. ”

“ And the chief facts in reproduction are practically the same wherever the phenomena occur. Here, as everywhere else in the world, when a new life-form appears, it is always the result of the union of two forces, elements, germs or whatsoever. ”

“ Yet if the term "sexual instinct" is held to comprise the whole series of complex relationships which are manifest to us in numerous and specialised modes of behaviour, which ultimately lead to reproduction, and which have gradually become interwoven in the tissue of the race, there can be little doubt that the assumption is a reasonable one. ”

“ Comparison shows that there is, on the one hand, no essential distinction between ordinary growth and reproduction by budding, and, on the other hand, none except the necessity for impregnation to distinguish asexual from sexual reproduction. ”

“ The mass of 145the reproductive products with the uncertainty of fertilization has more and more been replaced by a controlled impregnation and an effective protection of the offspring. In this way part of the energy required in the production of eggs and sperma has been transposed into the creation of mechanisms for allurement and for protection of the young. Thus we discover the first instincts of art in animals used in the service of the impulse of creation, and limited to the breeding season. ”

“ Sexual reproduction does not essentially differ, as we have seen, from budding or self-division, and these processes graduate through the repair of injuries into ordinary development and growth; it might therefore be expected that every character would be as regularly transmitted by all the methods of reproduction as by continued growth. ”

“ Nature making no mistake, never putting on a fresh kind of leg, or head, or tail, but always tending to repeat and to return to the primitive type.
It is the same in sexual reproduction: it is a matter of perfectly common experience, that the tendency on the part of the offspring always is, speaking broadly, to reproduce the form of the parents. ”

“ From the very outset the great object of Nature to our human eyes seems to be primarily reproduction, in the long run, indeed, an effort after economy of method in the attainment of an ever greater perfection, but primarily reproduction. This tendency to reproduction is indeed so fundamental, it is impressed on vital organisation with so great a violence of emphasis, that we may regard the course of evolution as much more an effort to slow down reproduction than to furnish it with any new facilities.
We must remember that reproduction appears in the history of life before sex appears. ”

“ This life-form, thus started, grows according to the laws of its becoming more and more, until, at the expiration of a fixed period, which varies greatly in different animals, it becomes a complete young individual, of the nature and kind of its parents. The fertilization of the ovum in the female is called conception; its growing state is called gestation, and its birth, on becoming a separate being, is called parturition. In its growing condition, and before its birth, the new young life form is known as the foetus. ”

“ The object of reproduction certainly constitutes no part of the sexual impulse whatever in any animal apart from man, and it reveals a lack of the most elementary sense of biological continuity to assert that in man so fundamental and involuntary a process can suddenly be revolutionized. ”

“ How should we have imagined the possibility of fertilization for successive generations, of hermaphroditism, or of reproduction by fissure, etc., being found among the methods which Nature adopts for replenishing the earth, had we contented ourselves with an examination of the comparatively simple methods of ordinary sexual reproduction? ”

“ Now with the plants and the lower animals the reproduction is a process which demands no power of self-movement and no faculty of intelligence. That changes, however, with the animals so soon as the reproduction becomes sexual, in which two individuals are concerned, who have to unite in order to lay their eggs and sperm on the same spot outside of the body or to incorporate the sperm in the body of the individual carrying the eggs. ”