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CHAPTER X

HEREDITY

"Vom Vater hab' ich die Statur,
Des Lebens ernstes Führen;
Vom Mütterchen die Frohnatur
Und Lust zu fabuliren.

Urahnherr war der Schönsten hold,
Das spukt so hin und wieder.
Urahnfrau liebte Schmuck und Gold,
Das zuckt wohl durch die Glieder.

Sind nun die Elemente nicht

An dem Complex zu trennen;

Was ist denn an dem ganzen Wicht

Original zu nennen?”

-GOETHE, 1" Zahme Xenien," vi.

HEREDITY is the rule of persistence among organisms. The existence of such a law, or "ascertained sequence of events," is "Like produces like,"

a matter of common observation.

"Stature from father and the mood

Stern views of life compelling;

From mother, I take the joyous heart
And the love of story-telling.

"Great-grandsire's passion was the fair.
What if I still reveal it?

Great-grandam's, pomp and gold and show,
And in my bones I feel it.

"Of all the various elements

That make up this complexity,

What is there left when all is done,

To call originality?"

BAYARD TAYLOR's translation in part.

"Blood will tell," "Blood is thicker than water," these proverbs in all languages indicate the general fact that each organism is likely to resemble its parents, and that the basis of fundamental resemblance among organisms is found in kinship by blood. It is equally a matter of common observation that the law of heredity is inseparable from a law of variation. No one organism is quite an exact copy of another. The prevention of such a condition is one of the effects of the process of double parentage. • Except in certain exceptional forms in which parthenogenesis or hermaphroditism appear, each complex organism springs from two organisms of the same species: the one male, the other female. The resultant organism partakes of the qualities of each of these in some degree, and through these to a degree also it partakes of qualities of the parents or ancestors of each.

The phrase, "Kinship by blood," used in connection with all studies of heredity, is a survival of an ancient theory that the physical basis of heredity is found in the actual blood. "Blood is quite a peculiar juice," as was observed by Mephistopheles, but its peculiarities are not concerned with heredity. The function of blood is concerned with the nourishment of tissues and the removal of their waste. The actual vehicle of transfer of hereditary qualities, the physical basis of heredity, is found in structures within the protoplasm of the germ cell.

The germ cells, male or female, are alike in all characters · essential to this discussion. On the average, the potency of the male and the female cell is exactly the same, there being nowhere constant advantage of one sex over the other. Each cell, male. or female, is one of the vital units, or body cells, set apart for the special purpose of reproduction. It is not essentially different from other cells in structure or in origin, but in its potentialities. Its function is that of repeating the original organism, . "with the precision of a work of art."

Heredity is shown in the persistence of type, in the existence. of broad homologies among living forms, in the possibility of natural systems of classification in any group, in the retention of vestigial organs, in the early development and subsequent obliteration of outworn structures once useful to individuals of the race or type.

In a general way, the individual inherits from both parents • the common structure of organisms of the species to which it belongs. The special peculiarities of the individual organism

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are also inherited, but in much less certainty of degree. These traits belonging to a member of a single generation have a smaller "inheritance fund" on which to draw. In each generation some of these individual qualities are latent or recessive," others are potent or dominant." The recessive or ancestral characters reappear with a certain regularity. They may form a sort of mosaic, by mixing with other dominant traits, or they may make a more or less perfect blend. Resemblance to some remote ancestor occurs at times, being known as atavism. Each ancestor has some claim in the formation of the new individual, and behind the grandfather and grandmother dead hands from older graves call in their direction. The past · will never let go, though with each generation there is a deeper crust over it. These old claims grow less with time, because with each new generation there are twice as many of these competitors. Moreover past generations can affect the heredity. of the individual only through the agency of his immediate parents. Out of these elements Mr. Galton frames the idea of a mid-parent," a sort of center of gravity of heredity, though, as Dr. Brooks has observed, it is doubtful if this mid-parent is more than a logical abstraction. The bluer the blood in any. species, that is, the more closely alike the ancestors are, the more certain will be the personal resemblance among the descendants.

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But characters actually latent are very real in heredity. Dr. Brooks says:

"When a son of a beardless boy grows up and acquires a beard, we may say that he has inherited his grandfather's beard, but this is only a figure of speech, and he actually inherits the beard his father might have acquired, had he lived, nor would the case of a child descended from a series of ten or a hundred beardless boys be different."

It is, moreover, certainly true that a beard can be as well inherited from the mother-who has nonee-as from the father. The inheritance is that of the beard the mother might have developed had she been a man. And, in general, in matters of. heredity, the child is not derived from the parents as they actually are, but from the parents as they might have been. The traits transmitted in heredity are chosen from the whole line · of parental possibilities. And with the process of conception,

the union of the two parental germ cells, "the gate of gifts is closed." No trait or quality can ever be acquired of which at least the elements are not involved in the original inheritance.

"What is transmitted to the infant," observes Dr. Archdall Reid, "is not the modification [of the parent], but only the power of acquiring it under similar circumstances. The power to acquire fit modifications in response to appropriate stimulation is that which especially differentiates high animal organisms from low animal organisms."

Atavism or reversion is the process of "throwing back," by which in some degree an individual resembles a distant ancestor. Under the name of "atavism," according to Yves Delage, are included three very different things:

(a) The transmission in one family of individual characters, which, latent for several generations, suddenly reappear. This is family atavism, and its nature is readily recognized.

(b) The reappearance, more or less regularly in a race, of characters of an allied race, from which the first race may have been derived. This is race atavism. Of this nature are the zebra stripes sometimes seen in mules.

(c) The appearance of characters abnormal for the race in which they appear, but which are normal in other races supposed to be ancestral. This is atavism of teratology. An illustration is the occasional appearance in the modern horse of rudiments of additional toes, with partly developed hoofs.

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'Everything is possible in heredity," observes Delage. "One may always find examples of election, of blending (of mosaic), of combination, of resemblance direct, and of resemblance reversed. To give to these groupings the name of laws would be an abuse of language, since not one of these rules is exclusively true. In reality there is no law of resemblance be- ▾ tween a child and its parents. All is possible, from a difference so great that there is not a trait in common, to an almost perfect identity with one or the other parent, with every intermediate degree of blending of characters and combination of resemblances."

The name "telegony" is given to the supposed influence of the first male on the future offspring of the female. This theory of telegony rests mainly on a case of a mare which was first impregnated by a quagga, and whose subsequent colts from males of her own species had quagga-like markings. The supposed

facts on which the theory is based are inadequate or unproved, and it is probable that the phenomena called telegony have no real existence.

Equally uncertain are the phenomena known as "prenatal influences." In the process of evolution, the development of the female has brought her to be more and more the protector and helper of the young. She gives to her progeny not only her share of its heredity, but she becomes more and more a factor in its development. In the mammalia the little egg is retained long in the body and fed, not with food yolk, but with the mother's blood. The parent thus becomes an immediate and most important part of the environment of the young. In man, by the growth of the family the parental environment becomes a lifelong influence. The father as well as the mother becomes a part of it.

It has long been a matter of common belief that among⚫ mammals a special additional formative influence is exerted by the mother in the period between conception and birth. The patriarch Jacob is recorded as having made a thrifty use of this influence in relation to the herds of his father-in-law, Laban. This belief is part of the folklore of almost every race of intelligent men. In the translations of Carmen Silva, that gentle woman whom kind nature made a poet and cruel fortune a queen, we find these words of a Roumanian peasant woman:

"My little child is lying in the grass,

His face is covered with the blades of grass.
While I did bear the child, I ever watched
The reaper work, that it might love the harvests;
And when the boy was born, the meadow said,
"This is my child'

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In the current literature of hysterical ethics we find all sorts of exhortations to mothers to do this and not to do that, to cherish this and avoid that on account of its supposed effect on the coming progeny. Long lists of cases have been reported illustrating the law of prenatal influence. Most of these records serve only to induce scepticism. Many of these are mere coincidences, some are unverifiable, others grossly impossible. There is an evident desire to make a case rather than to tell the truth. The whole matter is much in need of serious study, and

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