Weismann, whose notion of the continuity of germ-plasm supposes that no
part of an organism generates any of the formative material which goes
to make up its offspring. This material is regarded in much the same
light as the sperm which the male parent confides to the keeping of the
female, according to the notion of the ancient world above referred to.
For, as Romanes states (page 26): "In each generation a small portion of
this substance [germ-plasm] is told off to develop a new body to lodge
and nourish the ever-growing and never-dying germ-plasm--this new body,
therefore, resembling its so-called parent body simply because it has
been developed from one and the same mass of formative material; and,
lastly, that this formative material, or germ-plasm, has been continuous
through all generations of successively perishing bodies, which
therefore stand to it in much the same relation as annual shoots to a
perennial stem: the shoots resemble one another simply because they are
all grown from one and the same stock."
Although Professor Weismann denies that acquired characters, that is,
individual peculiarities arising as the result of personal experience,
are transmitted, he admits that congenital characters, that is,
peculiarities with which an individual is born, are transmitted to
offspring. As congenital characters must, originally, have been
individual, it is not easy at first sight to perceive Weismann's real
meaning. It is necessary, therefore, to enter more particularly into a
consideration of his theory, which he regards as in general accord with
Darwin's theory of pangenesis. Darwin supposes that all the cells of the
body continually give off great numbers of _gemmules_, which are
conveyed by the blood and deposited in the germ-cells of the organism.
These cells are thus endowed with the power of developing a new organism
of the same kind, each gemmule reproducing the cell from which it was
derived. These ultimate vital units are called by Weismann _biophors_,
but he supposes them not to be the ultimate "bearers of vitality." They
are said to be arranged in groups to which the term _determinants_ is
applied, and these groups are combined so as to form ancestral _ids_ or
germ-plasms. Each determinant, which is made up of perfectly definite
numbers and combinations of biophors, is the primary constituent of a
particular cell, or of a group of cells, such as a blood corpuscle. The
determinants thus "control the cell by breaking up into biophors, which
migrate into the cell body through the nuclear membrane, multiply there,
arrange themselves according to the forces within them, and determine
the histological structure of the cell," impressing upon it its
inherited specific character. The structure of the cell, and of every
subsequent stage, exists therefore potentially in the inherited
structure of the id, and the determination of its character "depends on
the biophors which the corresponding determinant contains, and which it
transmits to the cell."
GERM-PLASM.--While Weismann regarded germ-plasm as absolutely stable,
the only mode by which congenital variation could be brought about was
that of _amphimixis_, or intermingling of individuals in the process of
generation. As modified, however, by his latest work, "The Germ-plasm, a
Theory of Heredity," published in 1892, his theory now allows the plasm
to be capable of modification, and he ascribes that variation to the
direct effects of external influences on the biophors and determinants
of the germ-plasm. The instability of this substance is so slight,
however, that congenital variations cannot be acted on and perpetuated
by natural selection, and the influence of amphimixis is thus required
for the purpose. Mr. Herbert Spencer, however, in criticising
Weismann's theory, declares that "functionally produced modifications of
structure are transmissible," and he refers in support of his contention
to the remarkable effect of arrested nutrition on the structure and
habits of wasps and bees. It especially affects the reproductive organs,
and hence there is no occasion to call in the aid of amphimixis to
perpetuate the variations produced, its office being the blending of the
elements on which the characteristics of offspring depend.
If it be asked how modifications are actually transmitted, we may say
that it can be only by an affection of the germ-cell. This probably
takes place by deviations in the structure of what Weismann calls
determinants, or of groups of determinants, through rearrangement of
their primary units. The modification would be preceded, however, by a
corresponding change in the nerve centers concerned in the use or disuse
of the organs affected. Mr. Spencer shows that under certain conditions
changes take place in the conduct of certain insects, and that "the
maternal activities and instincts undergo analogous changes,"[77:A]
facts which point to a loss of nervous energy and to an intimate
connection between the nervous system and the reproductive function. Use
or disuse first increases or diminishes the activity of certain nerve
centers, and this leads to a modification of the corresponding
germ-cells. If so, the determinants, instead of being first affected, as
proposed by Weismann, and thus determining the variations, are in
reality modified as the result of the functional changes, and are thus
capable of transmitting these changes to succeeding generations.
In a subsequent article, published in _The Contemporary Review_ for
October, 1894, Mr. Spencer recapitulates his argument in favor of the
transmission of acquired characters, and refers to observations made by
Professor Hertwig and others, which he regards as "showing, firstly,
that all the multiplying cells of the developing embryo are alike; and,
secondly, that the soma-cells of the adult severally retain, in a latent
form, all the powers of the original embryo-cell," facts which he
rightly considers disproves Weismann's hypothesis of _panmixia_. If this
is surrendered, then, says Mr. Spencer, "all that evidence collected by
Mr. Darwin and others, regarded by them as proof of the inheritance of
acquired characters, which was cavalierly set aside on the strength of
this alleged process of panmixia is reinstated. And this reinstated
evidence, joined with much evidence since furnished, suffices to
establish the repudiated interpretation."
Great stress was laid by Professor Weismann, as evidence in support of
his theory, on the supposed fact that the inheritance of injuries
sustained during life has not been proved. Particular attention has been
paid to this point by Dr. Eimer, in relation to which he remarks: "That
injuries incurred during life are but seldom transmitted to the
offspring does not appear to me wonderful: the inheritance of the
complete form and complete activities of the organism, which took root
such enormously long periods of time ago, and has been strengthened at
each generation, will, as a rule, counterbalance in the offspring any
such injuries incurred only once and not repeated."[79:A] This is the
same argument as was used, as quoted above, by Professor Cope, to
disprove the occurrence of birthmarks, and Dr. Eimer goes on to state
that there are injuries which are not transmitted to offspring, although
they are constantly repeated, as an instance of which he refers to the
rupture of the hymen. He adds, however: "In such cases we must presume a
specially effective power of correlative activity, directed to the part
affected and residing in the whole organism--the same compensating power
which leads in lower animals, during the life of the individual, to the
regeneration of parts which have been lost or artificially removed. But
these cases do not prove the general proposition that injuries are not
inherited; they do not prove that even injuries which have been
repeated during a considerable period are not inherited. Hitherto little
importance has been attached to the demonstration of the inheritance of
injuries. Yet single cases of the inheritance of injuries only once
incurred seem to me to be thoroughly authentic."
CONGENITAL DEFORMITIES.--Professor Weismann, in replying to the
criticisms of Professor Virchow, admitted the existence of a number of
congenital deformities, birthmarks and other individual peculiarities,
which are inherited, but he affirms that we do not know from what causes
they first appeared, and that a great proportion of them proceed from
the germ itself, and are due, therefore, to alteration of the germinal
substance. There is no proof of this, however, according to Dr.
Eimer,[80:A] who appeals to various facts in support of his contention
that injuries and diseases are inherited. He thinks the degeneration of
the tail in the higher mammals is a case in point, although it has
required great periods of time to complete. Among other instances of
inherited injuries mentioned by Dr. Eimer is one in which a scar over
the left ear and temple, caused to a girl by being thrown from a
carriage, was transmitted to her son and grandson, the son of the latter
also showing absence of hair on the injured spot, although the defect
gradually disappeared with him, nearly a hundred years after the
accident. The case of Dr. Nosseler, who inherited from his mother a
crushed finger joint, caused by an accident which happened two years
before his birth, would seem to be conclusive proof that injuries are
transmissible. Dr. Eimer refers also to the breeding of short-tailed
pointers from dogs whose tails had been artificially shortened; and also
to Brown-Sequard's experiments with guinea pigs, in which epilepsy was
inherited by their offspring, who showed also the loss of certain
phalanges, or even whole toes of the hind feet, the parents having
suffered a similar loss owing to the division of the sciatic nerve. He
adds that numerous other instances of the inheritance of injuries have
been recorded, as "inheritance of the artificially shortened tail of the
bull, of artificially produced hornlessness in cattle, many cases of
inheritance in man of curvature in a finger, caused by injury,
inheritance of the absence of one eye which had been lost by the father
during life or by disease, etc."
The question of the inheritance of deformities and diseases, and the
causes of the germ-variations on which it depends, have been considered
by Zeigler, whose conclusions, as quoted by Dr. Eimer (page 186), are
too important to be omitted. The causes which Zeigler assigns for the
origin of such germ-variations are of three kinds. These are: 1--Union
of sexual nuclei which are not adapted for copulation; 2--Disturbance of
the copulatory process itself; 3--Injurious influences which affect the
sexual nuclei or the fertilized ovum at a time when separation of the
sexual cells from the body cells has not yet occurred. "If the embryo is
injuriously affected at a later period," says Zeigler, "either a
malformation or a constitutional anomaly arises, which is not inherited,
or only the sexual cells are injured, in which case the body-cells
develop normally, and a disturbance shows itself only in the development
of the next generation." The union of sexual nuclei not adapted for
copulation appears, however, to be "the most frequent and most important
cause of hereditary local malformations as well as of hereditary morbid
tendencies, or of a defect in any system of the whole organism." If the
nuclei are altogether unadapted to each other, sterility occurs, as in
the sexual nuclei of distinct species.
PSYCHICAL DISEASES.--Zeigler's conclusions are supported by reference to
the enquiries of the distinguished psychiatrist, D. Von Krafft-Ebings,
who has considered the heredity of psychical diseases, and in connection
therewith mentions three "essential facts" which it is necessary to keep
in view when dealing with that subject. The first of these facts is
Atavism, by which "the bodily and mental organization and character can
be transmitted from the first to the third generation, without any
necessity that the second and intermediate one should exhibit the
peculiarities of the first--thus the condition of the life and health of
the grandparents are of interest for us." Secondly, "Only in rare cases
is the actual disease transmitted in procreation (congenital insanity,
hereditary syphilis), as a rule only the disposition thereto. Actual
disease only occurs when accessory injurious influences produce an
effect based upon that disposition. . . . We must, therefore, consider
also the state of health of the relatives (uncles, cousins, aunts), and
since here also the law of atavism holds good, the possible diseases of
great-uncles and great-aunts." Thirdly, Dr. Von Krafft-Ebings says,
"Only exceptionally does the same disease develop in ascendant as
in descendant lines, in consequence of the transmission of morbid
dispositions. On the contrary, there exists a remarkable variability in
the forms of disease which may almost claim the value of a law (the law
of polymorphism or transmutation)."
This law is referred to by M. Ribot as one of the causes of deviation
from heredity, and he speaks of it as "transformation." As examples of
transformation of heredity, Ribot refers to fixed ideas in the
progenitor, which may become in the descendants "melancholy, taste for
meditation, aptitude for the exact sciences, energy of will, etc.;" the
mania of progenitors may be changed in the descendants into "aptitude
for the arts, liveliness of imagination, quickness of mind,
inconsistency in desires, sudden and variable will." "Just as real
insanity," says Moreau of Tours, "may be hereditarily reproduced only
under the form of eccentricity, may be transmitted from progenitors to
descendants only in modified form, and in more or less mitigated
character, so a state of simple eccentricity in the parent--a state
which is no more than a peculiarity or a strangeness of character--may
in the children be the origin of true insanity. Thus in transformations
of heredity we sometimes have the germ attaining its maximum intensity;
and again, a maximum of activity may revert to the minimum."[84:A]
It should be borne in mind, as mentioned by Von Krafft-Ebings,[84:B]
that everything which debilitates the nervous system and the generative
powers of the parents, "be it immaturity or too advanced old age,
previous debilitating diseases (typhus, syphilis), mercurial treatment,
alcoholic and sexual excesses, overwork, etc., may give rise to
neuropathic constitutions, and thereby indirectly to every possible
nervous disease in the descendants."
TELEGONY.--There is one remarkable phenomenon, spoken of by various
writers as _telegony_, which has an important bearing on the subject of
the transmission of acquired characters, and shows the action of
prenatal influence in an unexpected form. It is referred to by Professor
Romanes, when he says, "It has not unfrequently been observed, at any
rate in mammals, that when a female has borne progeny to a male of one
variety, and subsequently bears progeny to a male of another variety,
the younger progeny presents a more or less unmistakable resemblance to
the father of the older one."[85:A] This curious fact was considered, in
relation to plants especially, by Darwin, who affirms, as quoted by
Romanes, that it is of the highest theoretical importance, as "The male
element not only affects, in accordance with its proper function, the
germ, but at the same time various parts of the mother-plant, in the
same manner as it affects the same parts in the seminal offspring from
the same two parents. We thus learn that an ovule is not indispensable
for the reception of the influence of the male element."
The curious phenomenon of telegony is not limited, however, to plants.
Mr. Herbert Spencer drew attention, in _The Contemporary Review_ for
March, 1893, to a case which has long been known to horsebreeders, and
which may be said to have become classic. The facts were brought, by the
Earl of Morton, to the attention of the Royal Society of Great Britain,
as long ago as the year 1820. The Earl, who possessed a male quagga,
said, in a letter to the President: "I tried to breed from the male
quagga and a young chestnut mare of seven-eighths Arabian blood, and
which had never been bred from; the result was the production of a
female hybrid, now five years old, and bearing, both in her form and in
her colour, very decided indications of her mixed origin. I subsequently
parted with the seven-eighths Arabian mare to Sir Gore Ouseley, who has
bred from her by a very fine black Arabian horse. I yesterday morning
examined the produce, namely, a two-year-old filly and a one-year-old
colt. They have the character of the Arabian breed as decidedly as can
be expected, where fifteen-sixteenths of the blood are Arabian; and they
are fine specimens of that breed; but both in their colour and in the
hair of their manes they have a striking resemblance to the quagga.
Their colour is bay, marked more or less like the quagga in a darker
tint. Both are distinguished by the dark line along the ridge of the
back, the dark stripes across the forehead, and the dark bars across the
back part of the legs." Mr. Spencer refers to an analogous case of the
influence of a wild boar over the subsequent progeny of a domestic sow,
and it now appears that such effects are not so uncommon as the
scientific world has supposed.
Professor Romanes made particular enquiries on this subject of
professional and amateur breeders of animals, and he says most of his
correspondents "are quite persuaded that it is of frequent occurrence,
many of them regard it as a general rule, while some of them go so far
as to make a point of always putting a mare, bitch, etc., to a good
pedigree male in her first season, so that her subsequent progenies may
be benefited by his influence, even though they be engendered by
inferior sires."[87:A] His own more modest conclusion is that the
evidence he obtained "is enough to prove the fact of a previous sire
asserting his influence on a subsequent progeny, although this fact is
one of comparatively rare occurrence."
The English Darwinian met with only one case in which the offspring of a
woman by a second husband, who was a white man, showed the influence of
her first husband, who was a negro. Mr. Herbert Spencer would seem to
have been more successful. In _The Contemporary Review_ for May, 1893,
Mr. Spencer gives the result of his own enquiries as to the effect on a
white woman's subsequent progeny of a previous union with a negro, and
he quotes the opinion of a "distinguished correspondent," that
information given to him many years ago was to the effect that "the
children of white women by a white father had been _repeatedly_ observed
to show traces of black blood, in cases where the woman had previous
connexion with [i. e., a child by] a negro." Mr. Spencer refers also to
Professor Marsh as authority for such a case, and to the opinion of
several medical professors who assured him, through Dr. W. J. Youmans,
that the alleged result "is generally accepted as a fact." He gives as
authoritative testimony the following statement by Dr. Austin Flint,
taken from his "Text-book of Human Physiology:" "A peculiar and, it
seems to me, an inexplicable fact is, that previous pregnancies had an
influence upon offspring. This is well known to breeders of animals. If
pure blooded mares or bitches have been once covered by an inferior
male, in subsequent fecundations the young are likely to partake of the
character of the first male, even if they be bred with males of
unimpeachable pedigree. What the mechanism of the influence of the first
conception is, it is impossible to say; but the fact is incontestable.
The same influence is observed in the human subject. A woman may have,
by a second husband, children who resemble a former husband, and this is
particularly well marked in certain instances by the color of the hair
and eyes. A white woman who has had children by a negro may
subsequently bear children to a white man, these children presenting
some of the unmistakable peculiarities of the negro race."
This phenomenon would alone seem to answer the question of the
transmission of acquired characters in the affirmative, for its
explanation is to be found in the facts brought out by Darwin, as to the
action of foreign pollen on the structure of the mother plant; in
relation to which Professor Romanes remarks: "When one variety
fertilizes the ovules of another not unfrequently the influence extends
beyond the ovules to the ovarium, and even to the calyx and
flower-stalk, of the mother plant. This influence, which may affect the
shape, size, colour, and texture of the somatic tissues of the mother,
has been observed in a large number of plants belonging to many
different orders."[89:A] May we not have here the explanation of the
fact, which has frequently been pointed out, that husband and wife show
a tendency to grow like each other, both physically and mentally, the
resemblance after a long married life being sometimes very striking?
POWER OF HEREDITY.--The most important fact brought out in the
discussion of the possibility of the transmission of acquired characters
is the power of heredity. If organisms did not reproduce their own
special characteristics, there could be no fixity of form and no order
in organic nature. Nevertheless, if there were no change by individual
modification or divergence, in whatever way this may be rendered
permanent in the race, there could be no evolution. Hence we can say,
with Dr. Eimer, "Any one who thus completely renders allegiance to the
supremacy of the principles of the unity of the organic world, who
rejects everything which contradicts that principle, cannot help
admitting that in truth, as I assert, the ultimate origin of the various
kinships in the animal and vegetable kingdom is to be traced to
individual differences, and that the difference between the former, like
the latter, must be essentially determined by external conditions, by
the modification of organic growth."
The causes of diversity which interfere with the action of heredity may
operate, as we have seen, at the moment of conception, or subsequent to
conception. The former class of causes is of great importance, in
accordance with the principle, laid down by M. Ribot, of the
disproportion of effects to causes, and it is essential, therefore, if
children are to be well-born, that their parents should be careful that
at the moment of procreation they are fitted for the performance of so
serious an act. Mr. J. F. Nisbet in his "Marriage and Heredity" (page
126), well observes, "Twins usually bear a closer resemblance to each
other than to their brothers and sisters born at a different period;
and the reason generally assigned is that they are conceived under
precisely similar conditions. If so, it follows that the difference
existing between ordinary members of a family is due to their being born
at considerable intervals of time and therefore under changed conditions
on the part of their parents."
SOBRIETY IN THE FATHER.--Especially does it concern the father, who is
the most active agent in reproduction, to see that he is then in a fit
condition. This is quite apart from the question of the diseased
condition of the organism treated of by Dr. Von Krafft-Ebings, and
refers to temporary rather than to continuing causes. Sobriety is in
this connection of great importance, and, as appears from a passage,
already quoted, in Xenophon, was insisted on at the time of procreation,
by the ancients.