practice during the course of a life-time,—and, in truth, very
remarkably improved. If we could explain the existence of great talent,
such as, for example, a gift for music, painting, sculpture, or
mathematics, as due to the presence or absence of a special organ in
the brain, it follows that we could only understand its origin and
increase (natural selection being excluded) by accumulation, due to the
transmission of the results of practice through a series of
generations. But talents are not dependent upon the possession of
special organs in the brain. They are not simple mental dispositions,
but combinations of many dispositions, and often of a most complex
nature: they depend upon a certain degree of irritability, and a power
of readily transmitting impulses along the nerve-tracts of the brain,
as well as upon the especial development of single parts of the brain.
In my opinion, there is absolutely no trustworthy proof that talents
have been improved by their exercise through the course of a long
series of generations. The Bach family shows that musical talent, and
the Bernoulli family that mathematical power, can be transmitted from
generation to generation, but this teaches us nothing as to the origin
of such talents. In both families the high-water mark of talent lies,
not at the end of the series of generations, as it should do if the
results of practice are transmitted, but in the middle. Again, talents
frequently appear in some single member of a family which has not been
previously distinguished.
Gauss was not the son of a mathematician; Handel’s father was a
surgeon, of whose musical powers nothing is known; Titian was the son
and also the nephew of a lawyer, while he and his brother, Francesco
Vecellio, were the first painters in a family which produced a
succession of seven other artists with diminishing talents. These facts
do not, however, prove that the condition of the nerve-tracts and
centres of the brain, which determine the specific talent, appeared for
the first time in these men: the appropriate condition surely existed
previously in their parents, although it did not achieve expression.
They prove, as it seems to me, that a high degree of endowment in a
special direction, which we call talent, cannot have arisen from the
experience of previous generations, that is, by the exercise of the
brain in the same specific direction.
It appears to me that talent consists in a happy combination of
exceptionally high gifts, developed in one special direction. At
present, it is of course impossible to understand the physiological
conditions which render the origin of such combinations possible, but
it is very probable that the crossing of the mental dispositions of the
parents plays a great part in it. This has been admirably and concisely
expressed by Goethe in describing his own characteristics—
Vom Vater hab’ ich die Statur
Des Lebens ernstes Führen,
Vom Mütterchen die Frohnatur
Die Lust zum Fabuliren, etc.
The combination of talents frequently found in one individual, and the
appearance of different remarkable talents in the various branches of
one and the same family, indicate that talents are only special
combinations of certain highly-developed mental dispositions which are
found in every brain. Many painters have been admirable musicians, and
we very frequently find both these talents developed to a slighter
extent in a single individual. In the Feuerbach family we find a
distinguished jurist, a remarkable philosopher, and a highly-talented
artist; and among the Mendelssohns a philosopher as well as a musician.
The sudden and yet widespread appearance of a particular talent in
correspondence with the general intellectual excitement of a certain
epoch points in the same direction. How many poets arose in Germany
during the period of sentiment which marked the close of the last
century, and how completely all poetic gifts seem to have disappeared
during the Thirty Years’ War. How numerous were the philosophers that
appeared in the epoch which succeeded Kant; while all philosophic
talent seemed to have deserted the German nation during the sway of the
antagonistic ‘exact science,’ with its contempt for speculation.
Wherever academies are founded, there the Schwanthalers, Defreggers,
and Lenbachs emerge from the masses which had shown no sign of artistic
endowment through long periods of time[53]. At the present day there
are many men of science who, had they lived at the time of Bürger,
Uhland, or Schelling, would probably have been poets or philosophers.
And the man of science also cannot dispense with that mental
disposition directed in a certain course, which we call talent,
although the specific part of it may not be so obvious: we may, indeed,
go further, and maintain that the Physicist and the Chemist are
characterized by a combination of mental dispositions which differ from
those of the Botanist and the Zoologist. Nevertheless, a man is not
born a physicist or a botanist, and in most cases chance alone
determines whether his endowments are developed in either direction.
Lessing has asked whether Raphael would have been a less distinguished
artist had he been born without hands: we might also enquire whether he
might not have been as great a musician as he was painter if, instead
of living during the historical high-water mark of painting, he had
lived, under favourable personal influences, at the time of
highly-developed and widespread musical genius. A great artist is
always a great man, and if he finds the outlet for his talent closed on
one side, he forces his way through on the other.
From all these examples I wish to show that, in my opinion, talents do
not appear to depend upon the improvement of any special mental quality
by continued practice, but they are the expression, and to a certain
extent the bye-product, of the human mind, which is so highly developed
in all directions.
But if any one asks whether this high mental development, acquired in
the course of innumerable generations of men, is not dependent upon the
hereditary effects of use, I would remind him that human intelligence
in general is the chief means and the chief weapon which has served and
still serves the human species in the struggle for existence[54]. Even
in the present state of civilization—distorted as it is by numerous
artificial encroachments and unnatural conditions—the degree of
intelligence possessed by the individual chiefly decides between
destruction and life; and in a natural state, or still better in a
state of low civilization, this result is even more striking.
Here again, therefore, we encounter the effects of natural selection,
and to this power we must attribute, at any rate, a great part of the
phenomena we have been discussing, and it cannot be shown that—in
addition to its operation—the transmission of characters acquired by
practice plays any part in nature.
I only know of one class of changes in the organism which is with
difficulty explained by the supposition of changes in the germ; these
are the modifications which appear as the direct consequence of some
alteration in the surroundings. But our knowledge on this subject is
still very defective, and we do not know the facts with sufficient
precision to enable us to pronounce a final verdict as to the cause of
such changes: and for this reason, I do not propose to consider the
subject in detail.
These changes—such, for example, as are produced by a strange
climate—have been always looked at under the supposition that they are
transmitted and intensified from generation to generation, and for this
reason the observations are not always sufficiently precise. It is
difficult to say whether the changed climate may not have first changed
the germ, and if this were the case the accumulation of effects through
the action of heredity would present no difficulty. For instance, it is
well known that increased nourishment not only causes a plant to grow
more luxuriantly, but it alters the plant in some distinct way, and it
would be wonderful indeed if the seeds were not also larger and better
furnished with nutritive material. If the increased nourishment be
repeated in the next generation, a still further increase in the size
of the seed, in the luxuriance of the plant, and in all other changes
which ensue, is at any rate conceivable if it is not a necessity. But
this would not be an instance of the transmission of acquired
characters, but only the consequence of a direct influence upon the
germ-cells, and of better nourishment during growth.
A similar interpretation explains the converse change. When horses of
normal size are introduced into the Falkland Islands, the next
generation is smaller in consequence of poor nourishment and the damp
climate, and after a few generations they have deteriorated to a marked
extent. In such a case we have only to assume that the climate which is
unfavourable and the nutriment which is insufficient for horses, affect
not only the animal as a whole, but also its germ-cells. This would
result in the diminution in size of the germ-cells, the effects upon
the offspring being still further intensified by the insufficient
nourishment supplied during growth. But such results would not depend
upon the transmission by the germ-cells of certain peculiarities due to
the unfavourable climate, which only appear in the full-grown horse.
It must be admitted that there are cases, such as the climatic
varieties of certain butterflies, which raise some difficulties against
this explanation. I myself, some years ago, experimentally investigated
one such case[55], and even now I cannot explain the facts otherwise
than by supposing the passive acquisition of characters produced by the
direct influence of climate.
It must be remembered, however, that my experiments, which have been
repeated upon several American species by H. W. Edwards, with results
confirmatory of my own in all essential respects, were not undertaken
with the object of investigating the question from this point of view
alone. New experiments, under varying conditions, will be necessary to
afford the true explanation of this aspect of the question; and I have
already begun to undertake them.
Leaving on one side, for the moment, these doubtful, and insufficiently
investigated cases, we may still maintain that the assumption that
changes induced by external conditions in the organism as a whole, are
communicated to the germ-cells after the manner indicated in Darwin’s
hypothesis of pangenesis,—is wholly unnecessary for the explanation of
these phenomena. Still we cannot exclude the possibility of such a
transmission occasionally occurring, for, even if the greater part of
the effects must be attributed to natural selection, there might be a
smaller part in certain cases which depends on this exceptional factor.
A complete and satisfactory refutation of such an opinion cannot be
brought forward at present: we can only point out that such an
assumption introduces new and entirely obscure forces, and that
innumerable cases exist in which we can certainly exclude all
assistance from the transmission of acquired characters. In most cases
of variation in colour we have no explanation but the survival of the
fittest[56], and the same holds good for all changes of form which
cannot be influenced by the will of the animal. Very numerous
adaptations, such, for instance, as occur in the eggs of animals,—the
markings, and appendages which conceal them from enemies, the complex
coverings which prevent them from drying up or protect them from the
injurious influence of cold,—must have all arisen entirely
independently of any expression of will, or of any conscious or
unconscious action on the part of the animals. I will not mention here
the case of plants, which as every one knows are unconscious, for they
are beyond my province. In this matter, there can be no suggestion of
adaptation depending upon a struggle between the various parts of the
organism (Roux)[57]. Natural selection cannot operate upon the
different epithelial cells which secrete the egg-shell of _Apus_, since
it is of no consequence to the animal which secretes the egg-shell
whether a good or a bad shell is produced. Natural selection first
operates among the offspring, and the egg with a shell incapable of
resisting cold or drought is destroyed. The different cells of the same
individual are not selected, but the different individuals themselves.
In all such cases we have no explanation except the operation of
natural selection, and if we cannot accept this, we may as well abandon
any attempt at a natural explanation. But, in my opinion, there is no
reason why natural selection should be considered inadequate to the
task. It is true that the objection has been lately urged, that it is
inconceivable that all the wonderful adaptations of the organism to its
surroundings can have arisen through the selection of individuals; and
that for this purpose an infinite number of individuals and infinite
time would be required; and stress is laid upon the fact that the
wished-for useful changes can only arise singly and very rarely among a
great number of individuals.
This last objection to the modern conception of natural selection has
apparently some weight, for, as a matter of fact, useful variations of
a conspicuous kind seldom appear, and are often entirely absent for
many generations. If we expect to find that qualitative changes take
place by sudden leaps, we can never escape this difficulty. But, I
think, we must not look for conspicuous variations—such as occur among
domesticated animals and plants—in the process of the evolution of
species as it goes on in nature. Natural selection does not deal with
qualitative but quantitative changes in the individual, and the latter
are always present.
A simple example will make this clearer. Let us suppose that it was
advantageous to some species—for instance the ancestors of the
giraffe—to lengthen some part of the body, such as the neck: this
result could be obtained in a relatively short time, for the members of
the species already possessed necks of varying length, and the
variations which form the material for natural selection were already
in existence. Now all the organs of every species vary in size, and any
one of them will undergo constant and progressive increase, as soon as
it acquires exceptional usefulness. But not only will the organ
fluctuate as a whole, but also the parts composing it will become
larger or smaller under given conditions, will increase or diminish by
the operation of natural selection. I believe that qualitative
variations always depend upon differences in the size and number of the
component parts of the whole. A skin appears to be naked, when it is
really covered with a number of small fine hairs: if these grow larger
and increase in number, a thick covering is formed, and we say that the
skin is woolly or furry. In the same way the skin of many worms and
Crustacea is apparently colourless, but the microscope reveals the
presence of a number of beautiful pigment spots; and not until these
have increased enormously does the skin appear coloured to the naked
eye. The presence or absence of colour and its quality when present are
here dependent upon the quantity of the most minute particles, and on
the distance at which the object in question is observed. Again, the
first appearance of colour, or the change from a green to a yellow or
red colour depends upon slight variations in the position or in the
number of the oxygen atoms which enter into the chemical combination in
question. Fluctuations in the chemical composition of the molecules of
a unicellular organism (for example) must continually arise, just as
fluctuations are always occurring in the number of pigment granules in
a certain cell, or in the number of pigment cells in a certain region
of the body, or even in the size of the various parts of the body.
All these quantitative relations are exposed to individual fluctuations
in every species; and natural selection can strengthen the fluctuations
of any part, and thus cause it to develope further in any given
direction.
From this point of view, it becomes less astonishing and less
inconceivable that organisms adapt themselves—as we see that they
obviously do—in all their parts to any condition of existence, and that
they behave like a plastic mass which can be moulded into almost any
imaginable form in the course of time.
If we ask in what lies the cause of this variability, the answer must
undoubtedly be that it lies in the germ-cells. From the moment when the
phenomena which precede segmentation commence in the egg, the exact
kind of organism which will be developed is already determined—whether
it will be larger or smaller, more like its father or its mother, which
of its parts will resemble the one and which the other, even to the
minutest detail. In spite of this, there still remains a certain scope
for the influence of external conditions upon the organism. But this
scope is limited, and forms but a small area round the fixed central
point which is determined by heredity. Abundant nourishment can make
the body large and strong, but can never make a giant out of the
germ-cell destined to become a dwarf. Unhealthy sedentary habits or
insufficient nourishment makes the factory-hand pale and stunted; life
on board ship, with plenty of exercise and sea air, gives the sailor
bodily strength and a tanned skin; but when once the resemblance to
father or mother, or to both, is established in the germ-cell it can
never be effaced, let the habit of life be what it will.
But if the essential nature of the germ-cell dominates over the
organism which will grow from it, so also the quantitative individual
differences, to which I referred just now, are, by the same principle,
established in the germ, and—whatever be the cause which determines
their presence—they must be looked upon as inherent in it. It therefore
follows that, although natural selection appears to operate upon the
qualities of the developed organism alone, it in truth works upon
peculiarities which lie hidden in the germ-cells. Just as the final
development of any predisposition in the germ, and just as any
character in the mature organism vibrates with a certain amplitude
around a fixed central point, so the predisposition of the germ itself
fluctuates, and it is on this that the possibility of an increase of
the predisposition in question, and its average result, depends.
If we trace all the permanent hereditary variations from generation to
generation back to the quantitative variations of the germ, as I have
sought to do, the question naturally occurs as to the source from which
these variations arose in the germ itself. I will not enter into this
subject at any length on the present occasion, for I have already
expressed my opinion upon it[58].
I believe however that they can be referred to the various external
influences to which the germ is exposed before the commencement of
embryonic development. Hence we may fairly attribute to the adult
organism influences which determine the phyletic development of its
descendants. For the germ-cells are contained in the organism, and the
external influences which affect them are intimately connected with the
state of the organism in which they lie hid. If it be well nourished,
the germ-cells will have abundant nutriment; and, conversely, if it be
weak and sickly, the germ-cells will be arrested in their growth. It is
even possible that the effects of these influences may be more
specialized; that is to say, they may act only upon certain parts of
the germ-cells. But this is indeed very different from believing that
the changes of the organism which result from external stimuli can be
transmitted to the germ-cells and will re-develope in the next
generation at the same time as that at which they arose in the parent,
and in the same part of the organism.
We have an obvious means by which the inheritance of all transmitted
peculiarities takes place, in _the continuity of the substance of the
germ-cells, or germ-plasm_. If, as I believe, the substance of the
germ-cells, the germ-plasm, has remained in perpetual continuity from
the first origin of life, and if the germ-plasm and the substance of
the body, the somatoplasm, have always occupied different spheres, and
if changes in the latter only arise when they have been preceded by
corresponding changes in the former, then we can, up to a certain
point, understand the principle of heredity; or, at any rate, we can
conceive that the human mind may at some time be capable of
understanding it. We may at least maintain that it has been rendered
intelligible, for we can thus trace heredity back to growth; we can
thus look upon reproduction as an overgrowth of the individual, and can
thus distinguish between a succession of species and a succession of
individuals, because in the latter succession the germ-plasm remains
similar, while in the succession of the former it becomes different.
Thus individuals, as they arise, are always assuming new and more
complex forms, until the interval between the simple unicellular
protozoon and the most complex of all organisms—man himself—is bridged
over.
I have not been able to throw light upon all sides of the question
which we are here discussing. There are still some essential points
which I must leave for the present; and, furthermore, I am not yet in a
position to explain satisfactorily all the details which arise at every
step of the argument. But it appeared to me to be necessary to state
this weighty and fundamental question, and to formulate it concisely
and definitely; for only in this way will it be possible to arrive at a
true and lasting solution of the problem. We must however be clear on
this point—that the understanding of the phenomena of heredity is only
possible on the fundamental supposition of the continuity of the
germ-plasm. The value of experiment in relation to this question is
somewhat doubtful. A careful collection and arrangement of facts is far
more likely to decide whether, and to what extent, the continuity of
germ-plasm is reconcilable with the assumption of the transmission of
acquired characters from the parent body to the germ, and from the germ
to the body of the offspring. At present such transmission is neither
proved as a fact, nor has its assumption been shown to be
unquestionably necessary.
------------------------------------------------------------------------
Footnotes for Essay II.
Footnote 33:
Pflüger, ‘Ueber den Einfluss der Schwerkraft auf die Theilung der
Zellen und auf die Entwicklung des Embryo,’ Arch. f. Physiol. Bd.
XXXII. p. 68, 1883.
Footnote 34:
Victor Hensen in his ‘Physiologie der Zeugung,’ Leipzig, 1881, p. 216.
Footnote 35:
That is for the preservation of its life.
Footnote 36:
Compare Weismann, ‘Die Entstehung der Sexualzellen bei den
Hydromedusen,’ Jena, 1883.
Footnote 37:
It is doubtful whether _Magosphaera_ should be looked upon as a
mature form; but nothing hinders us from believing that species have
lived, and are still living, in which the ciliated sphere has held
together until the encystment, that is the reproduction, of the
constituent single cells.
Footnote 38:
Or is an exception perhaps afforded by the nutritive cells of the
egg, which occur in many animals?
Footnote 39:
Or more precisely, they must give up as many molecules as would
correspond to the number of the kind of cell in question found in the
mature organism.
Footnote 40:
See Darwin, ‘The Variation of Animals and Plants under
Domestication,’ 1875, vol. ii. chapter xxvii. pp. 349-399.
Footnote 41:
To this class of phenomena of course belong those acts of will which
call forth the functional activity of certain groups of cells. It is
quite clear that such impulses do not originate in the constitution
of the tissue in question, but are due to the operation of external
causes. The activity does not arise directly from any natural
disposition of the germ, but is the result of accidental external
impressions. A domesticated duck uses its legs in a different manner
from, and more frequently than a wild duck, but such functional
changes are the consequence of changed external conditions, and are
not due to the constitution of the germ.
Footnote 42: