Part 5

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.

In experimenting on moths it has been found that the _variations of temperature_ to which the pupæ, and probably also the larvæ, are subjected, tend to bring about very pronounced differences in the moths. Cold has a tendency to develop a darker hue in the perfect insect.

English dogs when taken to hot climates, like that of India, are known to degenerate in a few generations. It is well known how climate affects the hairiness of animals. When greyhounds are taken to the uplands of Mexico they are unable to course on account of the rarity of the air.

In 1870 a number of pupæ of a certain species of moth (Saturnia) were taken from Texas to Switzerland. After passing the winter there, the pupæ emerged from their cocoons as moths, and resembled the Texan species entirely. The young of these moths were fed on the leaves of a plant different from that the moths in Texas feed on, and they developed into moths so different in form and color-pattern from their parents that entomologists classified them as a distinct species.

We have seen how certain foods affect the germ-cells and act as blastogenetic factors; the preceding case and the following show how _certain foods act as somatogenetic factors_ and modify the body-cells. If the bullfinch be fed on hemp seed, its color is changed to black; if the canary be fed on cayenne, its plumage becomes darker; if the common green Amazonian parrot be fed on the fat of siluroid fishes, it assumes a beautiful variegation of red and yellow.

The _character of the soil_ has a marked influence in inducing somatogenetic variations. In France an experimenter collected seed from the wild radish and sowed one lot in heavy soil in the country, while another lot was sown by him in the dry, light soil near the Museum of Natural History in Paris. The radish “roots” grown in these two places presented marked differences in color and form. Those grown in Paris were either of a rose or white color and elongated; while those from the country were violet, dark-brown or nearly black in color, and more rounded than the former.

In the summer of 1847 Professor Buckman gathered seed from wild parsnips, and sowed them in the spring of 1848 under changed conditions of life. Most of the plants grown from these seeds were like the wild parsnips, but some of them developed the light-green color and hairless, smooth appearance characteristic of the cultivated plant. The roots also were found to be more fleshy than those of the wild variety.

Peas and squashes, when grown in different soils, often show remarkable variations.

There is one species of shrimp that inhabits brackish water, and another that lives in water which is much more salt. These crustaceans differ from one another in the character of the spines they bear and in the form of the tail-lobes. They have been regarded as distinct species, and yet either of them can be transformed into the other in the course of a few generations, by gradually altering the saline conditions of the water.

For a long while the siredon and amblystoma were regarded as being distinct genera of amphibians. Siredon was looked upon as a permanent gill-breather, while amblystoma passes through a metamorphosis and becomes a permanent lung-breather. It is now known that the former can change into the latter. If there is plenty of water the siredon remains indefinitely a gill-breather and reproduces freely; but when the water dries up it changes into the lung-breathing amblystoma. These two cases illustrate very well the power of environment to modify the development of organic forms.

As to “_use_” and “_disuse_”: It can readily be observed that exercise increases the size of muscles; that by steady application the capacity for thinking can be developed; that the oarsman’s constant use of his hands leads to the hardening and thickening of the cuticle; that the arm of the blacksmith and the legs of the mountaineer are much enlarged, etc.

When an organ is exercised properly, there is an increased blood supply to it, and, consequently, stimulated nutrition and growth in various parts, such as in the muscular, nervous or other tissues.

When an organ is disused there is diminished blood supply, and, consequently, diminished growth and functional capacity. In man it is known that certain activities, such as coal-heaving, shoemaking, etc., produce recognizable effects upon the muscular system, the skeleton, and other parts of the body.

The peculiar habits of a tribe, such as tree-climbing among those natives of the interior of New Guinea, who build their houses in the upper limbs of lofty trees, modify the body in ways that are readily recognizable.

After considering many facts in connection with the brains of rabbits, Darwin announced that this most complicated and important organ in an animal is subject to the law of decrease in size from disuse. We have very interesting illustrations of the effects of “use” and “disuse” in causing somatogenetic variations, in the differences between domestic ducks and the wild ones from which they have been undoubtedly derived. The wild duck, which must constantly be on the alert for enemies, and uses its wings so much more extensively and its legs comparatively less than the domestic duck, is a much more intelligent fowl than the stupid, well-protected domestic one. The wings of the wild duck are stronger and its legs shorter than those of the barnyard duck. It has been shown that in the wild duck the brain is nearly twice as heavy in proportion to the body as it is in the comparatively imbecile domestic duck.

Many other useful illustrations of disuse, such as the cattle and goats in India, that have dependent ears; also cats in China, and horses in parts of Russia, whose ears are dependent, could be referred to. Use and disuse are included among the factors of environment, because by those terms we mean certain _groups of body-cells that are functionally active or inactive_; for body-cells on any theory of modified pangenesis constitute an exceedingly important environment of the germ-cells.

The surrounding conditions (environment) of an animal or plant having the power to cause variations in the living creature by affecting its germ-cells or its body-cells, the _environment_ may be spoken of as _blastogenetic_ and _somatogenetic_.

Whether it is a fact or not that somatic variations can induce corresponding variations in the germ-cells, and thus be transmitted by heredity, it is certainly true that all heritages must come through the germ-cells. For this reason, it is clearly seen that so far as evolution is concerned the germ-cells are the factors of fundamental importance in organisms. Therefore, we may repeat that environment is the sum-total of the conditions of life that affect the germ-cells directly or indirectly.

ACQUIRED CHARACTERS.

All heritages, then, are derived directly through the germ cells. Can there be any heritages indirectly from the somatic cells through the germ-cells, as has hitherto been assumed? In other words, can acquired characteristics be transmitted to the offspring? This question has given origin to the battle royal that is still going on between opposing schools of biology. The contending parties have appealed to such biological evidence as is furnished by a study of use-inheritance, reflex and instinctive actions in animals, etc., and to such experimental evidence as the induction of traumatic epilepsy in guinea pigs, a change in the shape of the ear by cutting the cervical sympathetic nerve, protrusion of the eyeball through injury to the restiform body of the brain, and such like, noting the effects on the offspring, and have drawn very different conclusions.

As to the transmission or non-transmission of acquired characters, some have maintained that only germinal variations are transmitted (because they believe the germ cells are _insulated_ from the body cells, and therefore from somatic influences). For instance, Ziegler, in his work on _General Pathology_, says: “If a disease, such as nearsightedness, is the product of a special inherited predisposition, _plus_ the effect of harmful influences which have acted upon the body during life, only that part can be transmitted which was received by inheritance, but not that part which was derived from external influences.” In other words, there is no transmission of acquired character. In this belief it will be observed that he follows Weismann.

On the contrary, other investigators, like Darwin and Spencer, teach that somatic variations—the plus element in Ziegler’s illustration of nearsightedness—do influence the germ-cells (through some such agency as Darwin’s theory of pangenesis suggests), and that, therefore, acquired characters can be transmitted. The question is one of fundamental importance, and yet no crucial experiment has been devised or fact observed which can compel the correct answer. The evidence seems to favor the view that acquired characters can be transmitted.

The theories as to the transmission or non-transmission of acquired characters may be better understood by reference to schemes No. 1, 2 and 3. Scheme No. 1 represents the theory of =Pangenesis=, which teaches that reproductive cells are not formed from pre-existing reproductive cells, but by the body cells themselves. Darwin taught that all the cells of the body, such as skeletal-cells, muscle-cells, nerve-cells, and so on, are continually giving off infinitely small cell germs or gemmules, which have the power of growing and forming cells exactly like themselves. These gemmules have a great affinity for one another, and, circulating in the blood in countless numbers, they finally come together in the reproductive glands and form the reproductive cells. On this theory the fact of the transmission of acquired characters can readily be appreciated, and it can easily be understood how the parent molds the child. Suppose, for instance, that the parent, by exercise, has become a skillful athlete. In him certain muscles have become greatly developed and strengthened. During all the time of the exercise of these muscles, the modifying muscle cells have been continually giving off to the blood modified gemmules, which collect in the reproductive cells and make it possible for the offspring to develop into an athlete because the modified gemmules develop into modified muscles like those of the athlete.

Scheme 1 shows the absence of any arrow like those shown in schemes 2 and 3, directly connecting germ-cell with germ-cell; this means that in this theory there is no continuity of the germ-cells. But arrows are seen extending from the various body-cells (skeletal, glandular, etc.) to the germ-cell; this means that the germ-cells are formed by influences or gemmules emanating from the various body cells.

Scheme 2 teaches that a germ-cell (when fertilized, of course) can produce many cells, some of which differentiate, finally, into skeletal cells, some into glandular, some into muscle and nerve cells, and some into new germ-cells; so that an animal or plant, I, is formed. In like manner a germ-cell of animal, I, can give rise to the germ and body cells of animal, II, and so on indefinitely. This scheme shows that there is a direct =continuity of the germ-cells=; and it also shows that the germ-cells are entirely _insulated_, as it were, from the body-cells (skeletal, glandular, etc.), inasmuch as no influences (arrows) extend from the body-cells to the germ-cells. This means that the transmission of acquired characters, bodily, mental, moral, etc., is impossible. It means, in other words, that none of the advantages gained by a parent in the course of his life can be handed on to his offspring by heredity. There are many biologists and pathologists who teach this theory as the correct one.

The majority of biologists accept the theory illustrated in Scheme 3. This is the theory of =modified Pangenesis=, which teaches that there is a direct continuity of the germ-cells and that these germ-cells are not insulated from the body-cells, but that the latter, when modified as the result of experience, can send off influences that correspondingly modify the germ-cells; so that the latter, when developing into a new individual, may cause the same body variations that exist in the parent. In short, this scheme illustrates not only that there is a _germinal inheritance_, but also an _inheritance of acquired characters_. In this Scheme 3, the oblique arrows show that germ-cells produce other germ cells; the perpendicular arrows show that the germ-cells are modified by influences that proceed from the body cells.

_Germinal characteristics are transmitted with vastly greater amplitude and swiftness than merely body (acquired) characteristics._ If, for instance, a man were born with that physical constitution that makes with ease a first-class pianist out of him, his sons may easily, through heredity, be first-class pianists. But if a man be born without such a congenital tendency and has by constant labor and practice so developed the muscles of his forearm, his nerves, his brain, etc., that he becomes a very good pianist (acquired characters); and, further, if his male descendants for thousands of generations, in succession, have become very good pianists by constant practice, we may expect that the sons of these last generations may obtain a congenital tendency to become first-class pianists quite easily. The constant improvement, by practice, of groups of body-cells (muscle-cells, nerve-cells, etc.) for generations, has, in each generation, tended to so correspondingly modify the germ-cells that they have acquired the power to develop into men who may become very good pianists with very little practice. This illustrates that there may be a continuous summation of feeble germ-cell variations that have been induced by prolonged influences emanating from somatic variations, so that, in the course of many generations, robust acquired characters may ultimately be translated into strong congenital characters (Scheme 3).

Scheme 1. =Illustrating the theory of Pangenesis.= Here the germ-cell (a) develops into the body-cells, e, e, e, e, of animal I, as indicated by the oblique arrows, but not into any germ-cells, as indicated by absence of arrow between germ-cell (a) and germ-cells (b). The germ-cells (b) in animal I are formed by the aggregation of infinite numbers of gemmules from the various groups of body-cells, e, e, e, e, as indicated by the perpendicular arrows. The germ-cell (a) transmits germinal heritages to the body-cells e, e, e, e; these body-cells transmit the heritages to the germ-cells (b) by means of the gemmules. If the body-cells are modified in any way, correspondingly modified gemmules are sent to the germ-cells (b), and these germ-cells are modified and thus transmit acquired characters to animal II, and so on.