How Human Sexual Life Developed
( Originally Published 1940 )
a) The Asexual Period of Evolution
In this chapter we shall touch on a question to which, so far, too little attention has been paid by the scientific world and which nevertheless is certainly one of the most important fundamental problems of the whole of Biology-the origin of the sexual life.
In embryology at first one only knows vegetative growth and the vegetative method of reproduction. We must now try to find out what was the first cause for the sexual method of reproduction to develop side by side with the vegetative method.
On account of its superiority in the Darwinian sense, the sexual method later entirely superseded all vegetative methods of reproduction in the higher species of animals.
A brief review of its evolution will best demonstrate this. In recent times sexual processes in lower organisms have been carefully studied, but the asexual stage, the most primitive of all, has up to the present been greatly neglected. We shall now endeavour to repair this omission as far as possible, even if only hypothetically at first; proofs will then be further adduced from present day experimentation.
The first, most primitive forms of animal and vegetable life, which lived in water or moisture, were, as is now generally admitted, unicellular organisms; just as nowadays the most primitive form of life, such as bacteria, yeast-cells, many algae, amoebae, etc., still exist as unicellular organisms in countless quantities.
They grow by the absorption of nutritive substances, and when such a cell at last becomes too big and powerful to remain organised as one single cell, it reorganises itself and splits into two new individuals: an increase in number which is quite in accordance with the ordinary vegetative growth, and which, if the process is repeated at short intervals, may become very considerable, although quite asexual.
Indeed through their immense energy of growth, their countless numbers, their simple and frugal mode of life, and their almost limitless powers of resistance, these unicellular organisms have always in competition with the higher forms of animal and vegetable life shown themselves to be the most indestructible. And all our later complicated organisms, no matter how superior they may 186
be by virtue of their higher differentiation, are, mankind included, often defenceless against these tiny intruders, to whom we ourselves must finally fall victim; and only cremation itself destroys both the intruders and the victims.
All our modern hygiene does not serve to bring us a free pardon, but only a postponement of our execution. But when the organic world had already long been in existence and had collected here and there large quantities of organic waste matter, it must often have happened that somewhere or other fruitful soil was produced, a fertilisation by means of which the plant world (and as a secondary consequence, the animal world also) was enabled to develop more luxuriantly than before.
This modification of growth, the formation of multicellular organisms, signified at that time a new era in the organic world with possibilities of evolution hitherto unsuspected. From the unicellular green algae strands were evolved which under favourable conditions grow continually longer and may even branch. By their side parasitic colourless fibres of mould formed, as if they were descended directly from the colourless bacteria. The multicellular animal organ-isms, too, then found an excess of vegetable substance available as nutriment, and so were able to assume greater dimensions.
It is very remarkable, and I will state at once that with sexual phenomena it is always the same story.
Firstly, some hypertrophic growth as an external expression of greatly increased reserve energy, and then a separation into single cells, as an adequate expression of the impossibility of a further growth. Thus we nearly always have in the first place a tumour-like formation, and indeed in the higher plants the formation of flower-buds, in the higher animals the formation of testes and ovaries, by means of which in due course the reproductive cells will be expelled just like the spores in the case of the inferior organisms.
The majority of these innumerable spores are hopelessly lost; so their vest numbers are not of much use. Furthermore, spore formation, like everything sexual, is only localised in a circumscribed spot, while at the beginning the vegetative reproduction represents a general function of the whole body. Thus in the phenomenon of sex the increase in numbers does not seem to be the most important thing; the phenomenon of sex is rather an adaptation to the economic conditions; it is indeed no rejuvenescence, but an emigration on a large scale!
b) The Sexual Period of Evolution
Up to the present we have considered only the asexual period of evolution, at most including spore-formation as the first attempt of nature to come to the rescue when ruin threatened. Thus we sketched out a scheme of vegetative evolution. But now we come to the period in which the phenomenon of sex becomes ever more prominent.(1) Because we have the good fortune to live in this latter period, the history of evolution from now on will be much less hypothetical.
The fusion of two ordinary cells occurs as a transition stage to the actual sexual phenomenon even in fairly low forms of life.
We call these organs the "sexual organs" and describe as female those which produce the fewer nut larger cells with abundant store of nutriment, and as male those which cast off numerous small cells without reserve nutriment. The difference between the cells makes chemotactic attraction of the one for the other particularly striking. In higher plants a pollen-cell eagerly combines with an egg-cell, and the higher animals a sperm-cell with an egg-cell.
The different characters of the two conjugating cells and their origin in two different organs, cause a far greater differentiation in the descendants than the copulation of two similar cells. But at first there was still a certain amount of uniformity because the two combining cells had been produced by one common individual, or else by two individuals who were both bisexual and consequently almost identical.
In the history of evolution this is the hermaphroditic period of transition.
In the further course of the history of evolution hermaphrodism has also had to yield to the separation of the sexes. This is the usual process of differentiation, according to the principle of the division of labour. The transition is evident. When by chance in one of the hermaphrodite individuals one sex, and in another individual the other sex, temporarily or permanently fails, then the surviving function can develop all the more strongly in such individuals. Such functionally specialised individuals (for we humans are all specialised in one or the other sex) must eventually survive in the struggle for existence.
The first appearance of such one-sided development may at first, apart from accidental or individual peculiarities, quite easily have been occasioned by great variations in the nutritive conditions of the various individuals. We have already seen that luxuriant growth favours the formation of females and vice versa. I shall now also refer to Prantl's experiments, which show distinctly how immensely important a part is played by nutritive conditions in the history of sexual evolution.
Prantl found when he sowed the spores of the fern "Osmunda Ceratopteris" in soil very rich in nitrogen, that he did not get the ordinary hermaphroditic prothallia, but only prothallia with exclusively female organs. In soil extremely poor in nitrogen he only obtained prothallia with male organs. So he could at will, simply by modifying the conditions of the plant nutrition, convert the old hermaphrodite stage into one of separate sexuality, and even deliberately choose the sex.
In the animal world especially the separation of the two sexes has gained the victory. This has enabled the difference of the sexes to appear with its rivalry and its special lures, by means of which a higher civilisation and greater perfection were produced. And this is undoubtedly the reason why the division of the sexes has had such an unqualified success in the animal world, but not in the plant world where there can be no question of a conscious sexual selection. In the plant world most flowers have remained bisexual. But even here self-fertilisation is avoided as far as possible by the most varied arrangements; only in the case of necessity it was a useful resource.
The existence of two distinct sexes, this fusion of two cells of different character, if they are both fit representatives of the same species, is the summit of the sexual life. We ourselves are living in this stage, and we owe it all to our advantages.
Only increase in numbers is rather retarded as a result of the sexual system. For reproduction has become dependent on the combined action of two individuals-a considerable complication in itself. And while in the unicellular organisms each cell-division causes a doubling of their numbers, the sexual fusion of two cells means a halving of the numbers each time. Especially in view of the vast number of reproductive cells, frequently as numerous as the sands on the sea-shore, we must come to the conclusion that in comparison with this number, the practical success of procreation may almost be considered as an exception; it is only a few that can be saved. For we see from actual experience that since in the history of evolution, the sexual life has assumed the task of pro-creation, the prolificacy of these higher species has constantly diminished. However, the biological and economical advantages of the sexual method are enormous and constant.
If, however, two dissimilar cells fuse, then besides the above-mentioned advantages, there will also be an enormous increase in the variability, because among the resulting offspring some will display more of the father's peculiarities, and some more of the mother's.
And even this variability betokens an immense progress in the struggle for existence; for no matter what further events or catastrophes may befall an animal or vegetable species, there will now always be found amongst the members of the same species some individuals which have become more resistant to these prejudicial influences and more capable of adapting themselves to a new environment... Thus there will almost always be some individuals saved; the species will not so easily be lost in tote.
On the contrary, precisely on account of this evolution in a different direction, according to the different environment to which they must adjust themselves, natural selection constantly chooses new varieties and new species as better adapted. So we can see why since the time of Linnaeus the classification especially of the higher species of plants and animals is principally ruled by the sexual organs. It is because this great variety of forms of life has only been evolved through the variability produced by the sexual life.
The tremendous influence for improvement exerted by this fusion of two dissimilar cells is shown in the most striking manner by a comparison of this function with the efforts of the cattle breeder in crossing, or of the gardener in grafting and budding. If the Iatter, for instance, grafts a tree that is strong but rather wild, and yields much fruit of small size, on to one of a more cultivated and delicate kind, which bears less fruit of larger size, then as a general rule the better properties of both will persist, while the inferior qualities of both will be effaced.
So also may be explained that enigma in mankind, which has so often filled us physicians with astonishment, that in the poorest of proletariat families, where in the course of time the germ-plasm must certainly be damaged in many ways ,as a result of constitutional exhaustion and all kinds of toxic influences, children are often born as perfectly formed and healthy in appearance as the best-looking child of a well-to-do family. It is only a pity that on account of the unfavourable environment, these advantages are so soon neutralised; but each new fertilisation is an effort of Nature to come to the rescue.
It is therefore not surprising that this sexual growth-modification which has such a salutary and refining effect in the struggle for existence, has gradually taken the upper hand.
Of course, at first the occurrence of the phenomenon of sex may have been a rare exception, even an anomaly consequent of internal exhaustion; a reversion, an atavism, through which rescue of the species is rendered possible. Indeed, even now in many of the lower forms of animal and vegetable life the purely vegetative growth is still the rule, the sexual phenomenon an exception.
But the more highly the plants and animals develop, the more inevitably must the limit of their possibility of growth be reached sooner or later; and so also in the plants that stand, on a somewhat higher level, sexual reproduction has become the rule, instead of being the exception. Indeed, in the higher order of plants, asexual reproduction has decreased to such an extent, that just as formerly sexual reproduction was the exception, so now in these higher forms of plants asexual multiplication has become an exception that only occasionally occurs in shoots and trees through accidental wounding, or artificially through grafting and cutting.
In the animal world we also observe the same course of evolution, which here, however, has more rapidly become general. Asexual reproduction was superseded in the animal world at an early period by sexual, and this higher stage of evolution soon made such progress that any further asexual reproduction was out of the question. So much so indeed that we are now always inclined to regard all reproduction and increase of numbers as being a matter of sex.
If we now briefly review the whole history of the evolution of the species, it becomes evident that the sexual life represents a constantly reappearing regeneration. The importance of this cannot be overestimated.
Is it not a fact that when we look back over our past lives, we often long to begin our education all over again? And what a blessing it would be if a scholar could be put back again into the elementary class. Well, Nature does not argue about it; she acts. We have hardly begun to realise that some stagnation and regression are sooner or later unavoidable, when Nature already proceeds to the creation of a new generation of unicellular organisms, so that these may begin the whole process of evolution over again from the very first stages. And then in about nine months she repeats the whole history on a large scale in the formation of the succeeding multicellular generation. This is a true regeneration each time, with renewed energy and renewed possibilities of happiness. Compared with all other factors of evolution, this constant sexual rebirth must certainly be regarded as an evolutionary factor of the first order.
The whole history of evolution of cell-life now takes on a new aspect for us. It shows itself as a continual play of exchanges between two complementary vicarious phases: the vegetative and the sexual. But the transition from one phase to another; the change from the vegetative method of growth to the sexual and vice versa does not take place so easily. Very often influences must always arise before there is a stoppage in the continuity.
And then we understand how the sexual function can manifest itself in so many different ways: in the multifarious forms and colours of the flowers, in men and animals: psychically by the most powerful impulses, and physically by the most extraordinary attitudes and the most complicated efforts.(3) Also that this function may find expression in such a fundamentally different variety of way: alone, during sleep, together with another individual of the same or opposite sex, even by the employment of almost every conceivable object with or without life.
The strength of the resistance that must be overcome shows us clearly why it is that the sexual impulse is so invigourating for the adult; just as a mother finds herself so invigourated after a confinement. In this way the sexual life acts both physically and psychically as a powerful uplifter, imbuing us with the highest degree of life-energy.
Just as in plants the sexual life represents the closing scene of a leaf-bud formation, in many of the lower animals it only appears at the close of their existence; the male often dies soon after the act of copulation and the female as soon as she has laid her eggs. In the higher animal world and in mankind something similar is to be observed. For though the casting off of the reproductive cells is not delayed until the end of life, yet it does not appear until the close of the youthful period of growth.
The whole situation is entirely different in the animal body only because the latter is quite differently constructed. The body of a plant always exhibits, just as before the beginning of all sexual life, an organisation of parts of equal value; in the higher plants there is a series of stem-segments or internodes, constantly forming new segments until finally the formation of flowers appears. But since in animals the sexual method of reproduction has become the only one possible, the number of segments has become limited, and they have all grown together in one single concentrated and enclosed organisation, by means of which a far higher division of labour is rendered possible.
On account of this central organisation, the animal body reacts to harmful influences much more energetically than a plant. At the slightest local infection by dangerous substances (for instance, bacterial poisons), a number of unicellular organisms (the pus corpuscles), form in the body, and then find their way out through ducts or by some destruction of tissue.
And so we see that just as in plants, so too in the animal body, the sexual crisis is called forth as a means of salvation by a certain condition of exhaustion.
This argument is splendidly confirmed by the counter-proof.
If, exceptionally, the vegetative growth is not hindered, the sexual growth-modification does not occur.
The more luxuriantly the vegetative life develops, the trees in superfluous masses of leaves, and mankind in superfluous fat, the less may great fecundity be expected. And breeders dread obesity in animals wanted for reproductive purposes, or in hens for laying.
But when the vegetative growth of a luxuriantly growing tree is injured in some way or other, for instance if a few roots or branches are lopped off roughly, so that it begins to droop some-what, it then starts to bear fruit.
The control-test is differently manifested in man. As soon as a woman has passed the period of fertility, it almost invariably happens, as with castrated men, that she begins to put on fat.
Practically, this principle has long been known as a sort of rivalry between two diverging functions; the sexual and the vegetative growth. Gardeners have taken advantage of this principle from time immemorial. In order to produce flowers instead of leaves, they place their plants in the smallest pots, with an abundance of light and sunshine. The control-test as a proof of this is easy to perform. I once planted, in a flower-bed that lay partly in the shade, some pelargoniums in pots, carefully putting a flat stone under the hole in the bottom of the pot, and raising the rim of the pot a little above the ground, so that the roots could not grow beyond the pot. They all bore plenty of flowers, except two which stood in the shade, and these had too many leaves and no flowers at all. When winter came, and I took up the pots, I found that these two had managed to push through and had strong roots in the soil beneath. Only here the symptoms of exhaustion and with them the flower-formation were absent.
Countless examples of this diverging effect might be drawn from horticultural practice ; sharp bends made in the stems of branches of fruit trees trained on walls and trellis work; carrots pulled up by the roots at the end of the first year and transplanted in a sunny spot with plenty of manure, so that they should produce few leaves but plenty of seed; and all transplanting of seedlings with the same object.
When grape-vines and fruit trees are pruned, if it is properly done, a rich crop of fruit is obtained at the expense of the leaf-formation.
The Japanese gardeners follow the same principle in the production of their dwarf trees; they sow the smallest seeds in the smallest possible pots, the roots are kept very short from the first, the soil as poor and small in quantity as possible, with a minimum of moisture. They thus succeed in growing fruit in a nut-shell.
We need not, however, go so far as Japan for examples! Who has not noticed, when clearing his garden-path of weeds, how between the hard gravel the tiniest plants often grow ; real dwarfs, deprived of moisture and nutriment, yet still blooming in the hot sunshine with more flowers than leaves!
Thus we obtain a thorough insight into the contrast between the vegetative and the sexual growth. The different value of these two complementary phases of evolution lies in the difference of their needs and products. That which is good for one often injures the other, and vice versa; and on that account the functions are divergent.
Now that we are able to trace the causal nexus of the sexual growth modification, we can go on to enquire which factors favour and which hinder the vegetative or the sexual growth.
This knowledge is of the highest practical importance in the breeding of all animals and the cultivation of all plants. By its means we may possibly succeed in time in human education also in postponing the sexual crisis, that turning point in our lives, for a while, so that first the vegetative, and then the sexual life may flourish and come to perfection.
Of course, the majority of living conditions can affect both phases of evolution in a similar way. Therefore, the popular idea is not so erroneous that, in general, favourable living conditions will produce both luxuriant growth and a good yield of flowers. This holds good only for moderate influences which are beneficial in every respect ; but not for excessive influences which border on the pathological. These may have a one-sided effect.
In mankind we can study this question thoroughly in all cases of early puberty and of retarded sexual maturity, of which ethnography affords us so many samples. The natives of tropical countries are precocious, although their health is so prejudicially affected by the climate and by social evils, because the stimulus from light and sunshine is maximal; but not those of polar regions, where all influences are unfavourable. Thus a comparatively early awakening of sexuality often occurs amongst the children of the working classes in our big towns, where the living conditions are just as faulty, but where an excess of sexual stimuli is felt.
This conception of the case is confirmed by the general educational experience of all ages, that a reasonably restricted but good nutrition, together with plenty of muscular exercise in the open air, with careful avoidance of artificial sexual stimuli, exerts the most happy influence in the prevention of precocious sexual maturity. In the simple life of rural districts, it has been noted from experience that a retarded sexuality occurs as frequently as precocity in the towns. Now we can understand the great importance of chastity in childhood, on which such great value has always rightly been set.
That in time we shall meet with practical success in this direction seems to me all the more hopeful because I believe that our higher civilisation compared with that of the primitive races, can already show some success in the course of the history of evolution.