Part 4
The complex nucleus of the fertilized ovum may be compared to a modern Italian building which has been constructed of material—a column here, a cornice there, a lintel yonder—gathered from different classic buildings of varying antiquity. In view of the increasing number of ancestral groups of hereditary units that must have accumulated in the nuclei of ova in the course of time, there must necessarily, for mechanical reasons, have arrived a period when these nuclei could receive no more of them by fertilization, unless natural selection should develop some saving device; hence we have, possibly, an explanation of the phenomena of maturation in ova (the _reducing process_ of Weismann and Hertwig). Here the ovum, prior to fertilization, undergoes mitosis twice in succession, by which the polar bodies are formed and the hereditary mass is diminished by one-half (the mature germ cells having only one-half the number of nuclear threads that the body cells possess). A homologous process takes place in the maturation of spermatozoids. Fertilization increases the amount of the hereditary mass in the ovum to the original quantity, and thus restores the number of nuclear threads to the specific number. All the body cells derived from the fertilized ovum possess, also, the specific number of threads.
This union of two distinct hereditary masses is called _amphimixis_ as well as _fertilization_.
Maturation and amphimixis or fertilization are _the source of many variations in the body_, good and bad, beautiful and ugly, geniuses and monstrosities; because, in the commingling of distinct hereditary masses, there is a struggle for existence between the hereditary units and a survival of the fittest.
In this struggle some of the hereditary units are strengthened so that heritages may be augmented; some mix so that there may be a blending of characteristics; some are mutually exclusive; some are prepotent; some are neutralized; some are destroyed; some lie dormant (latent) for varying lengths of time, and some are so altered as to produce much modified forms; and thus the possibilities of combination, reactions and modifications of the hereditary units, and therefore heritages, are almost endless.
The _augmentation of heritages_ in the fertilized ovum is well displayed, for instance, where fleet horses are bred with fleet ones, until, by careful selection, generation after generation, a progeny may be secured much more swift than the original stock from whence they were derived. In the same way good milch cows have been produced.
The mixing of hereditary units and _blending of heritages_ is shown in the color of the skin, as where a mulatto child is born to a negress by a white father; _mutually exclusive heritages_ are well illustrated in the color of the eyes, as where a child has either the blue eyes of one parent or the black of the other, but never any blending of the colors; this may also be illustrated where the white game bird and black one are crossed, the young being either white or black, but never blended. _Prepotency_ is illustrated where the silky variety of fan-tailed pigeon is mated with any other small-sized variety of pigeon, for the silkiness is invariably transmitted. A most interesting case of prepotency in mankind, mentioned by Ribot, is that of Lislet-Geoffrey, an engineer in Mauritius. He was the son of a very stupid negress and an educated white man. In physical constitution he was as much a negro as his mother; he had the woolly hair, the features, the complexion, and the peculiar odor of his race. He was so thoroughly a white man as regards intellectual development that he succeeded in vanquishing the prejudices of race, so strong in the French colonies, and in being admitted into the most aristocratic houses. At the time of his death he was Corresponding Member of the Academy of Sciences.
In this, it will be observed, we have prepotency in the mother’s physical constitution, and in the father’s intellectual characteristics.
The struggle of heritages in the impregnated ovum may lead to such structural changes of the nucleus, and therefore of the cell, as to develop the most marked variations—such variations as the biologists call _sports_.
In the latter part of the eighteenth century the farmers of Massachusetts had flocks of ordinary sheep on their farms. These sheep were continually jumping fences and getting on neighboring farms. They were the source of many disputes and much irritation between neighboring farmers. Finally, one of the sheep had a lamb which, when grown, displayed well-marked peculiarities (a sport). It had a longer body than the ordinary sheep and shorter legs, which were bowed. It was noticed that this sheep could not get over the fences. The cute Yankee farmer, noticing this valuable peculiarity, carefully preserved this peculiar sheep, and from it was ultimately derived, by careful selective breeding, a special variety known as the Ancon sheep.
The germinal variations resulting from the mixing of two separate hereditary masses by impregnation find their expression in the most varied qualities of the minds and bodies of developing children. If the variations are not especially marked, they are looked upon as normal and attract no special attention.
But if the variations are so pronounced as to compel attention, and at the same time it is known that they are useful, they are spoken of as talents, or, on the other hand, if they are harmful or useless, they are designated as pathological or monstrosities.
These are truly what the biologists call sports; and to those classes of sports that occur as specially gifted in human culture, in the varied fields of science, art, or literature, we assign such a person as Shakespeare, and call the remarkable variations embodied in him genius. On the other hand, such variations as lead to certain forms of pigmentary degeneration of the retina, and to Daltonism, to dyschromatopsia and achromatopsia, to certain supernumerary glands, polydactylism, and such like, which are either useless or harmful, we designate as pathological cases or monstrosities.
Hereditary units (the carriers of heritages) may be _latent_—that is, they may appear late in life, or in the offspring, or, still again, in remote descendants; in the latter cases the heritages are spoken of as reversional or _atavistic_. Latent hereditary units may very usefully be compared to dormant seeds buried in the ground. It is stated that buried seeds may lie dormant for many years, so that when a plot of ground is plowed deeply and upturned, plants that have not been seen there within the memory of one will often make their appearance and flourish. The hereditary units are veritable _living seeds_, that, under certain and often unknown stimuli, grow and unfold their heritages as do the buried seeds.
Latent heritages are well illustrated by a study of secondary sexual characters as developed at puberty.
Among our barnyard fowls, the hens often, when they have atrophy or degeneration of the ovaries, although up to this time they have laid eggs for years, stop this function, put aside the plumage and appearance proper to their sex, and don more or less completely the garments of the rooster. Thus females have latent in them many secondary sexual characters of the male. For similar reasons the male develops, occasionally, female characters.
This latency is illustrated again in deer. In most species of the deer tribe the males alone possess antlers, yet it is a well-known circumstance that in females with degenerations of the ovaries rudimentary horns that are never shed appear. A study of congenital color-blindness illustrates beautifully latent heritages, showing how the females of one generation may be free from the malady and the males of the next afflicted.
A study of the _regeneration of lost parts_ in various animals and plants illustrates well the latency of many hereditary units. A cutting made from the willow and planted sends out roots and finally reaches the dimensions of the adult tree. Here the body cells of the stem evidently contained, in a latent condition, many hereditary units in their nuclei, which became active through the special stimulus of being planted as a cutting. Adult plants can be raised from the cuttings of many other plants.
If the garden worm is cut in two, the head-part will reproduce the tail-portion. If the little fresh-water polyp, Hydra, be cut into a number of pieces, each segment will reproduce a perfect animal. Many lizards, after losing their tails by violence, manufacture new tails through the agency of the latent hereditary units contained in the body cells of the stump left. If the tentacle or “horn” of a snail, which contains an eye with a perfect lens and retina, be cut off, the animal can reproduce another one with a perfect eye, and this can be repeated a number of times. Often newts, when fighting with one another, or lobsters when fighting, lose a leg or a claw. These highly organized animals have the power of creating new limbs, making bones, ligaments, muscles, nerves, cuticle, and so on. All of this is done _through the hereditary masses in the nuclei of the body cells_ at the site of the injury.
A study of the phenomena of polymorphism in hydroids and insects will beautifully and most interestingly illustrate latent hereditary units.
Much that is speculative and fanciful is included under the subject of atavism, and the safest plan for pathologists and biologists, in considering any abnormality, is to remember a golden rule of Gegenbaur, that only those structures are reversional which are taxonomically not far distant or phylogenetically not very old. Embryology is also a very important check in considering such subjects.
In mankind supernumerary limbs and digits, microcephalia and micrencephalia, have been looked upon as reversions to the simian type.
Lombroso, in contrasting the criminal with normal man, looks upon his _homo delinquens_ as an illustration of atavism, contrasting with _homo sapiens_. But, as Ziegler, in his _Pathology_, well observes, many writers have gone too far in this respect, and have characterized as atavistic formations various acquired pathological formations and fresh variations of germ cells.
I think one can safely say that supernumerary ribs and those supernumerary nipples and mammary glands along the line of the deep epigastric and internal mammary arteries are truly atavistic structures; also certain muscles normally belonging to those mammalia which come near to man in the scale of relationship, and which appear in man as muscular variations, are reversional.
Children are often born with pigmented hairy patches on their bodies known as moles; sometimes these hairy moles are only of the size of a split pea, in other cases they are several square inches in area, while in rare cases almost all of the trunk may be thus covered. Although many similar pathological cases are often but marked variations called sports, yet the illustrations mentioned are undoubtedly reversional. Of the multitudinous illustrations of atavism that could be mentioned I wish to refer to but one more case.
The conjunctiva is a modification of skin, and frequently proclaims its ancestry by reverting to its original form. It is by no means a very rare event to see a patient having a patch of hair-covered skin growing upon the ocular conjunctiva. While a clinical assistant at the Royal Ophthalmic Hospital in London, we saw one such case, and Dr. Treacher Collins, the pathologist of that eye hospital, has stated that about twelve cases are seen there annually of this pathological condition, which is atavistic, according to Sutton, although it seemingly violates Gegenbaur’s rule about phylogenetic remoteness, and may be looked upon by some as a pathological illustration of a sport.
In speaking of inheritance, we should carefully discriminate between _heredity_ and _pseudo-heredity_. Physicians constantly write of tuberculosis, lepra, smallpox, and syphilis as hereditary; but it is incorrect and misleading to do so. When a person has syphilis, say, from the earliest existence—that is, from the fertilized ovum by transmission of a syphilitic microbe through the germ cells of the parents—this should be designated by its proper name as _congenital bacterial infection_. This is totally different from the hereditary qualities that flow from the structural equilibrium following the commingling and struggle for existence of multitudes of hereditary units.
The one set of hereditary qualities is _purely germinal_, while the other is germinal _profoundly modified by the presence of an infecting microbe_. Of course, to the extent that any toxines that are secreted by the bacteria may cause permanent structural changes in the germ-cells, to that extent may the germinal characteristics be transmitted and become hereditary.
Many instances of infection of the child _in utero_ have been reported in cases of endocarditis, scarlet fever, and smallpox; and there can no longer be any doubt, from experimental investigation and recent observation, that pneumococci, typhoid bacilli, anthrax bacilli, and pus cocci are able to pass to the fœtus through the placenta. But the diseases that develop in this way can be called hereditary with even less semblance of correctness than in the case of the fertilized ovum that is invaded with a microbe.
All of these cases are illustrations of pseudo-hereditary transmission, and should, for the sake of clearness and accuracy, be spoken of as _prenatal_ infections.
So far as the problems of heredity and variation are concerned, we may say that the life cycle begins and ends with the germ cell. Insects lay their eggs in old age; among plants the annuals flower but to die; in higher creatures the cessation of the procreative power often marks the beginning of bodily decline.
Bearing in mind that the human body consists of two great classes of cells, germ cells and somatic cells, the following scheme will be found very useful in discussing heredity with variation—viz.:
{ Stable { (Heredity) { Temperature. } { { Chemical } { { substances in } { { solution in the } Germ-Cell { { Blastogenetic { fluids that } { { { bathe the } { { { germ-cells, as } { { { food, drugs, } { Unstable { { poisons, etc. } { (Variation) { } Environment { { Habitat } { { Temperature } { { Climate } { { Air } { Somatogenetic { Food } { Soil } { Water } { “Use” } { “Disuse” }
Just in proportion as fertilized germ cells during the mitoses of ontogeny give origin, among the somatic cells, to other germ cells that are structurally, and therefore physiologically, like themselves, just to that extent do we have heredity; on the other hand, just to the degree that the new germ cells which are produced are unstable, to that degree also do we meet with variations.
ENVIRONMENT.
In zoölogy the environment of an organism means the sum-total of the conditions of life that surround and affect it, such as food, air, water, climate, etc.
We have already stated that as far as evolution is concerned the structures of fundamental importance in an organism are the Germ-Cells; therefore, for our purposes, we will define _environment to be the sum-total of the conditions that directly or indirectly influence in any way the germ-cells_, by which variations in them may be produced, or through which stability may be maintained.
There are two great classes of environmental factors that bring about variations in the germ-cells. One of these classes acts directly on the germ-cells, and is therefore called _blastogenetic_; the other acts indirectly through the body cells, and is therefore designated _somatogenetic_. Many of the blastogenetic factors bringing about structural changes in the delicate mechanism of germ-cells are entirely unknown, and are therefore designated as fortuitous. Many other causes, such as poisons in solution in the fluids that bathe them, can readily enough be appreciated.
=Blastogenetic Factors.= It has been demonstrated that various _chemical substances_, such as chloroform, morphia, chloral, etc., _have a pronounced influence upon the vital activities of cells_. It is well known that microscopic unicellular plants constitute the essential part of yeast. These little cells have the power of causing fermentation in solutions of grape sugar by which alcohol and carbon dioxide are formed, the latter being a gas and escaping as bubbles. If chloroform or ether be added to the solution of sugar, before adding the yeast, no fermentation takes place, for the yeast-cells are paralyzed. But when the yeast is separated from the chloroform solution and rinsed with distilled water, it soon regains the power of causing fermentation in pure solutions of sugar.
_Ova and Spermatozoids_ are subject to the action of drugs in a similar manner. If actively motile spermatozoids of a sea-urchin be placed in a one-half of one per cent. solution of chloral in sea water, it will be found that after five minutes their action will be completely arrested. These motions can soon be restored if the chloral solution be sufficiently diluted with pure sea water. These temporarily paralyzed spermatozoids, when completely recovered, will unite as quickly with ova as fresh spermatozoids. When spermatozoids are kept for half an hour in the chloral solution, a more decided paralysis will be observed, which persists for some time after the removal of the poisonous agent. A few minutes elapse before some of the spermatozoids exhibit feeble movements which finally become active. Even when placed near ova, it is some time before they fertilize them, although several may attach themselves to the egg’s surface. But, finally, fertilization does take place by the penetration of one spermatozoid, and the egg normally develops.
In like manner, if ova are subjected to chloral solution of varying strength, they also are influenced in a marked degree; for, when fertilized, they develop in an abnormal manner. Ordinarily, normal ova are fertilized by one spermatozoid. If fertilized by two or more, they become diseased, and develop pathologically. The chloral solution favors this fertilization by several spermatozoids. The stronger the solution of chloral, the larger the number of spermatozoids that fertilize the ovum. Experiment and observation show that the behavior of the nuclear hereditary mass is modified, during mitosis, by the chloral and other solutions. It is thus seen that _the germ-cells of the lower animals can be profoundly modified by various substances_.
Equally true is it that the man or woman who makes use of such drugs as alcohol, opium, chloral, and such like, in an intemperate manner, contains these poisons in solution in the blood, circulating to every part of the body, and thus bathing and profoundly influencing the germ-cells. In consequence of this fact an acquired and habitual intemperance will seldom fail to leave its impress upon one or more of the offspring, either like the original vice or one very closely allied to it. Intemperate people not only profoundly impair the health, the intelligence, and the morals of their offspring, by poisoning these delicate germ-cells, but they also transmit the fatal tendency to crave for the very substances that have acted as poisons on these germ-cells before and after fertilization. And one of the saddest features of this great medical truth is that the hereditary units which are concerned in transmitting these grave abnormal tendencies may lie dormant in the germs of one generation, to become active in those of the next; so that children of intemperate parents may lead honorable and temperate lives, and take every pains to rear, in turn, their own children in a wholesome and refining atmosphere, and yet these children of good environment may become intemperate through heredity, so that the sins of the grandparents may be visited, not on the children, but on the grandchildren.
These profound truths should lead all, and especially law-makers, to remember that “the man who inherits from his parents an impulsive or easily tempted nature and an inert will and judgment, and commits a crime under the influence of strong emotion, can no more be placed in the same category of responsibility with a man of more favorable constitution and temperament than can a man who steals a loaf under the pangs of starvation with a merchant who commits a forgery to afford him the means of prolonging a guilty career.”[3]
Not only do certain known poisons circulating in the blood, or other fluid that may bathe the germ-cells of living creatures, profoundly affect the germ-cells, but many other substances probably have great influence upon them. Certainly, the _amount and character of the food_ have a very decided influence on them, as will be understood from the following facts.
According to Yung, who has experimented very extensively upon tadpoles, all tadpoles pass through a bisexual (hermaphroditic) stage, as is the case probably with most animals. During this tadpole phase external influences, and, more particularly, food, determine their fate as regards sex. In Yung’s experiments it was found that when tadpoles were left to themselves, the percentage of females was in the majority, the average being probably about 57 per cent. females and 43 per cent. males. In experimenting with three broods, those fed on beef gave 78 per cent. females; those fed on fish gave 80 per cent. females; and those fed on the highly nutritious flesh of frogs gave 92 per cent. females.
In Mrs. Treat’s interesting experiments on moths and butterflies, it was observed that if caterpillars were confined and starved before they entered the chrysalis state, the resultant moths or butterflies were males, but others of the same brood that had been highly nourished came out females.
The study of bees illustrates the same conclusions. It is well known that in a beehive there are three kinds of inmates, as the queen, the drones, and the workers,—the last-mentioned being females whose reproductive organs are imperfectly developed. It is believed that the eggs that give rise to queens and workers are fertilized and developed normally. But it is a very curious fact that the eggs which develop into drones do so without fertilization (_parthenogenesis_). What factor or factors decide the destiny of the two former, determining whether a given ovum will develop into a queen, and thus be the possible mother of a new generation, or stay at the lower grade of a working, non-fertile female? These factors are the quality and quantity of the food. An abundance of what is called royal food causes the development of the larva in such a way that the queen with her reproductive organs is formed. If a larva on the road to develop into a worker (non-fertile female) “receive by chance some crumbs from the royal superfluity,” it is found that the reproductive organs may develop to such an extent that workers partially fertile may be formed. A worker larva may, by this royal food, be intentionally reared into a queen bee.
It is thus seen how profoundly the germ-cells, in their growth, may be affected and made to vary by such a blastogenetic factor as food.
=Somatogenetic Factors.= As to somatogenetic factors—granting that structural changes in the body (body-cells) of an animal or plant can profoundly influence in some way the germ-cells, and that, therefore, acquired characters can be transmitted—they are many and well defined. Some of them are the habitat of an animal or plant, the temperature, climate, air, food, soil, water, _structures in use or disuse_ (so-called “Use” and “Disuse”), etc.
The following brief descriptions will enable the reader to understand that change in the surroundings (environment) of a living creature may cause its body (body-cells) to vary.
A certain species of snail was introduced into Lexington, Virginia, a few years ago from Europe. In its new _habitat_ it varied very much. One hundred and twenty-five varieties have been discovered there, sixty-seven of which are new and unknown in Europe, the native home of the species.
The common ringed snake, when living in its natural habitat, deposits eggs in the sand, which are hatched by the heat of the sun; but when this snake is confined in a cage in which no sand is strewn, it gives birth to little living snakes.