psychology of man were made by Darwin in his fine work on _The Descent
of Man and Selection in Relation to Sex_, and again in his
supplementary work, _The Expression of the Emotions in Man and
Animals_. To understand the historical development of Darwin's
anthropology one must read his life and the introduction to _The
Descent of Man_. From the moment that he was convinced of the truth
of the principle of descent--that is to say, from his thirtieth year,
in 1838--he recognised clearly that man could not be excluded from its
range. He recognised as a logical necessity the important conclusion
that "man is the co-descendant with other species of some ancient,
lower, and extinct form." For many years he gathered notes and
arguments in support of this thesis, and for the purpose of showing
the probable line of man's ancestry. But in the first edition of _The
Origin of Species_ (1859) he restricted himself to the single line,
that by this work "light would be thrown on the origin of man and his
history." In the fifty years that have elapsed since that time the
science of the origin and nature of man has made astonishing progress,
and we are now fairly agreed in a monistic conception of nature that
regards the whole universe, including man, as a wonderful unity,
governed by unalterable and eternal laws. In my philosophical book
_Die Weltraetsel_ (1899)[151] and in the supplementary volume _Die
Lebenswunder_ (1904)[152] I have endeavoured to show that this pure
monism is securely established, and that the admission of the
all-powerful rule of the same principle of evolution throughout the
universe compels us to formulate a single supreme law--the
all-embracing "Law of Substance," or the united laws of the constancy
of matter and the conservation of energy. We should never have reached
this supreme general conception if Charles Darwin--a "monistic
philosopher" in the true sense of the word--had not prepared the way
by his theory of descent by natural selection, and crowned the great
work of his life by the association of this theory with a naturalistic
anthropology.
FOOTNOTES:
[Footnote 127: _Generelle Morphologie der Organismen_, 2 vols.,
Berlin, 1866.]
[Footnote 128: Eng. transl.; _The History of Creation_, London, 1876.]
[Footnote 129: London, 1908.]
[Footnote 130: Munich, 1884.]
[Footnote 131: _Die Mutationstheorie_, Leipzig, 1903.]
[Footnote 132: _Der Kampf der Theile im Organismus_, Leipzig, 1881.]
[Footnote 133: Leipzig, 1904.]
[Footnote 134: Berlin, 1876.]
[Footnote 135: _Wonders of Life_, London and New York, 1904.]
[Footnote 136: Eng. transl.; _The Evolution of Man_, 2 vols., London,
1879 and 1905.]
[Footnote 137: _Origin of Species_ (6th edit.), p. 396.]
[Footnote 138: Eng. transl.; _Facts and Arguments for Darwin_, London,
1869.]
[Footnote 139: 3 vols., Berlin, 1894-96.]
[Footnote 140: _Descent of Man_ (Popular Edit.), p. 927.]
[Footnote 141: _Gesammelte Abhandlungen zur wissenschaftlichen
Medizin_, Berlin, 1856.]
[Footnote 142: Eng. transl.; _Last Words on Evolution_, London, 1906.]
[Footnote 143: _Descent of Man_, (Popular Edit.), p. 255.]
[Footnote 144: _Descent of Man_, p. 930.]
[Footnote 145: Eng. transl.; _The History of Creation_, London, 1876.]
[Footnote 146: Berlin, 1894-96.]
[Footnote 147: Leipzig, 1874, 5th edit. 1905. Eng. transl.; _The
Evolution of Man_, London, 1905.]
[Footnote 148: London, 1898.]
[Footnote 149: _Festschrift zur 350-jaehrigen Jubelfeier der Thueringer
Universitaet Jena_. Jena. 1908.]
[Footnote 150: London, 1885; 1888.]
[Footnote 151: _The Riddle of the Universe_, London and New York,
1900.]
[Footnote 152: _The Wonders of Life_, London and New York, 1904.]
VI
MENTAL FACTORS IN EVOLUTION
BY C. LLOYD MORGAN, LLD., F.R.S
In developing his conception of organic evolution Charles Darwin was
of necessity brought into contact with some of the problems of mental
evolution. In _The Origin of Species_ he devoted a chapter to "the
diversities of instinct and of the other mental faculties in animals
of the same class."[153] When he passed to the detailed consideration
of _The Descent of Man_, it was part of his object to show "that there
is no fundamental difference between man and the higher mammals in
their mental faculties."[154] "If no organic being excepting man," he
said, "had possessed any mental power, or if his powers had been of a
wholly different nature, from those of the lower animals, then we
should never have been able to convince ourselves that our high
faculties had been gradually developed."[155] In his discussion of
_The Expression of the Emotions_ it was important for his purpose
"fully to recognise that actions readily become associated with other
actions and with various states of the mind."[156] His hypothesis of
sexual selection is largely dependent upon the exercise of choice on
the part of the female and her preference for "not only the more
attractive but at the same time the more vigourous and vicious
males."[157] Mental processes and physiological processes were for
Darwin closely correlated; and he accepted the conclusion "that the
nervous system not only regulates most of the existing functions of
the body, but has indirectly influenced the progressive development of
various bodily structures and of certain mental qualities."[158]
Throughout his treatment, mental evolution was for Darwin incidental
to and contributory to organic evolution. For specialised research in
comparative and genetic psychology, as an independent field of
investigation, he had neither the time nor the requisite training.
None the less his writings and the spirit of his work have exercised a
profound influence on this department of evolutionary thought. And,
for those who follow Darwin's lead, mental evolution is still in a
measure subservient to organic evolution. Mental processes are the
accompaniments or concomitants of the functional activity of specially
differentiated parts of the organism. They are in some way dependent
on physiological and physical conditions. But though they are not
physical in their nature, and though it is difficult or impossible to
conceive that they are physical in their origin, they are, for Darwin
and his followers, factors in the evolutionary process in its physical
or organic aspect. By the physiologist within his special and
well-defined universe of discourse they may be properly regarded as
epiphenomena; but by the naturalist in his more catholic survey of
nature they cannot be so regarded, and were not so regarded by Darwin.
Intelligence has contributed to evolution of which it is in a sense a
product.
The facts of observation or of inference which Darwin accepted are
these: Conscious experience accompanies some of the modes of animal
behaviour; it is concomitant with certain physiological processes;
these processes are the outcome of development in the individual and
evolution in the race; the accompanying mental processes undergo a
like development. Into the subtle philosophical questions which arise
out of the naive acceptance of such a creed it was not Darwin's
province to enter; "I have nothing to do," he said,[159] "with the
origin of the mental powers, any more than I have with that of life
itself." He dealt with the natural history of organisms, including not
only their structure but their modes of behaviour; with the natural
history of the states of consciousness which accompany some of their
actions; and with the relation of behaviour to experience. We will
endeavour to follow Darwin in his modesty and candour in making no
pretence to give ultimate explanations. But we must note one of the
implications of this self-denying ordinance of science. Development
and evolution imply continuity. For Darwin and his followers the
continuity is organic through physical heredity. Apart from
speculative hypothesis, legitimate enough in its proper place but here
out of court, we know nothing of continuity of mental evolution as
such: consciousness appears afresh in each succeeding generation.
Hence it is that for those who follow Darwin's lead, mental evolution
is and must ever be, within his universe of discourse, subservient to
organic evolution. Only in so far as conscious experience, or its
neural correlate, effects some changes in organic structure can it
influence the course of heredity; and conversely only in so far as
changes in organic structure are transmitted through heredity, is
mental evolution rendered possible. Such is the logical outcome of
Darwin's teaching.
Those who abide by the cardinal results of this teaching are bound to
regard all behaviour as the expression of the functional activities of
the living tissues of the organism, and all conscious experience as
correlated with such activities. For the purposes of scientific
treatment, mental processes are one mode of expression of the same
changes of which the physiological processes accompanying behaviour
are another mode of expression. This is simply accepted as a fact
which others may seek to explain. The behaviour itself is the adaptive
application of the energies of the organism; it is called forth by
some form of presentation or stimulation brought to bear on the
organism by the environment. This presentation is always an individual
or personal matter. But in order that the organism may be fitted to
respond to the presentation of the environment it must have undergone
in some way a suitable preparation. According to the theory of
evolution this preparation is primarily racial and is transmitted
through heredity. Darwin's main thesis was that the method of
preparation is predominantly by natural selection. Subordinate to
racial preparation, and always dependent thereon, is individual or
personal preparation through some kind of acquisition; of which the
guidance of behaviour through individually won experience is a typical
example. We here introduce the mental factor because the facts seem to
justify the inference. Thus there are some modes of behaviour which
are wholly and solely dependent upon inherited racial preparation;
there are other modes of behaviour which are also dependent, in part
at least, on individual preparation. In the former case the behaviour
is adaptive on the first occurrence of the appropriate presentation;
in the latter case accommodation to circumstances is only reached
after a greater or less amount of acquired organic modification of
structure, often accompanied (as we assume) in the higher animals by
acquired experience. Logically and biologically the two classes of
behaviour are clearly distinguishable: but the analysis of complex
cases of behaviour where the two factors cooeperate, is difficult and
requires careful and critical study of life-history.
The foundations of the mental life are laid in the conscious
experience that accompanies those modes of behaviour, dependent
entirely on racial preparation, which may broadly be described as
instinctive. In the eighth chapter of _The Origin of Species_ Darwin
says,[160] "I will not attempt any definition of instinct.... Every
one understands what is meant, when it is said that instinct impels
the cuckoo to migrate and to lay her eggs in other birds' nests. An
action, which we ourselves require experience to enable us to perform,
when performed by an animal, more especially by a very young one,
without experience, and when performed by many individuals in the same
way, without their knowing for what purpose it is performed, is
usually said to be instinctive." And in the summary at the close of
the chapter he says,[161] "I have endeavoured briefly to show that the
mental qualities of our domestic animals vary, and that the variations
are inherited. Still more briefly I have attempted to show that
instincts vary slightly in a state of nature. No one will dispute that
instincts are of the highest importance to each animal. Therefore
there is no real difficulty, under changing conditions of life, in
natural selection accumulating to any extent slight modifications of
instinct which are in any way useful. In many cases habit or use and
disuse have probably come into play."
Into the details of Darwin's treatment there is neither space nor need
to enter. There are some ambiguous passages; but it may be said that
for him, as for his followers to-day, instinctive behaviour is wholly
the result of racial preparation transmitted through organic heredity.
For the performance of the instinctive act no individual preparation
under the guidance of personal experience is necessary. It is true
that Darwin quotes with approval Huber's saying that "a little dose of
judgment or reason often comes into play, even with animals low in the
scale of nature."[162] But we may fairly interpret his meaning to be
that in behaviour, which is commonly called instinctive, some element
of intelligent guidance is often combined. If this be conceded the
strictly instinctive performance (or part of the performance) is the
outcome of heredity and due to the direct transmission of parental or
ancestral aptitudes. Hence the instinctive response as such depends
entirely on how the nervous mechanism has been built up through
heredity; while intelligent behaviour, or the intelligent factor in
behaviour, depends also on how the nervous mechanism has been modified
and moulded by use during its development and concurrently with the
growth of individual experience in the customary situations of daily
life. Of course it is essential to the Darwinian thesis that what Sir
E. Ray Lankester has termed "educability," not less than instinct, is
hereditary. But it is also essential to the understanding of this
thesis that the differentiae of the hereditary factor should be
clearly grasped.
For Darwin there were two modes of racial preparation, (_1_) natural
selection, and (_2_) the establishment of individually acquired habit.
He showed that instincts are subject to hereditary variation; he saw
that instincts are also subject to modification through acquisition in
the course of individual life. He believed that not only the
variations but also, to some extent, the modifications are inherited.
He therefore held that some instincts (the greater number) are due to
natural selection but that others (less numerous) are due, or partly
due, to the inheritance of acquired habits. The latter involve
Lamarckian inheritance, which of late years has been the centre of so
much controversy. It is noteworthy however that Darwin laid especial
emphasis on the fact that many of the most typical and also the most
complex instincts--those of neuter insects--do not admit of such an
interpretation. "I am surprised," he says,[163] "that no one has
hitherto advanced this demonstrative case of neuter insects, against
the well-known doctrine of inherited habit, as advanced by Lamarck."
None the less Darwin admitted this doctrine as supplementary to that
which was more distinctively his own--for example in the case of the
instincts of domesticated animals. Still, even in such cases, "it may
be doubted," he says,[164] "whether any one would have thought of
training a dog to point, had not some one dog naturally shown a
tendency in this line ... so that habit and some degree of selection
have probably concurred in civilising by inheritance our dogs." But in
the interpretation of the instincts of domesticated animals, a more
recently suggested hypothesis, that of organic selection,[165] may be
helpful. According to this hypothesis any intelligent modification of
behaviour which is subject to selection is probably coincident in
direction with an inherited tendency to behave in this fashion. Hence
in such behaviour there are two factors: (1) an incipient variation in
the line of such behaviour, and (2) an acquired modification by which
the behaviour is carried further along the same line. Under natural
selection those organisms in which the two factors cooeperate are
likely to survive. Under artificial selection they are deliberately
chosen out from among the rest.
Organic selection has been termed a compromise between the more
strictly Darwinian and the Lamarckian principles of interpretation.
But it is not in any sense a compromise. The principle of
interpretation of that which is instinctive and hereditary is wholly
Darwinian. It is true that some of the facts of observation relied
upon by Lamarckians are introduced. For Lamarckians however the
modifications which are admittedly factors in survival, are regarded
as the parents of inherited variations; for believers in organic
selection they are only the foster-parents or nurses. It is because
organic selection is the direct outcome of and a natural extension of
Darwin's cardinal thesis that some reference to it here is
justifiable. The matter may be put with the utmost brevity as follows:
(1) Variations (V) occur, some of which are in the direction of
increased adaptation (+), others in the direction of decreased
adaptation (-).
(2) Acquired modifications (M) also occur. Some of these are in the
direction of increased accommodation to circumstances (+), while
others are in the direction of diminished accommodation (-). Four
major combinations are
(_b_) + V with - M, (_c_) - V with + M,
(_a_) + V with + M, (_d_) - V with - M.
Of these (_d_) must inevitably be eliminated while (_a_) are selected.
The predominant survival of (_a_) entails the survival of the adaptive
variations which are inherited. The contributory acquisitions (+ M)
are not inherited; but there are none the less factors in determining
the survival of the coincident variations. It is surely abundantly
clear that this is Darwinism and has no tincture of Lamarck's
essential principle, the inheritance of acquired characters.
Whether Darwin himself would have accepted this interpretation of some
at least of the evidence put forward by Lamarckians is unfortunately a
matter of conjecture. The fact remains that in his interpretation of
instinct and in allied questions he accepted the inheritance of
individually acquired modifications of behaviour and structure.
Darwin was chiefly concerned with instinct from the biological rather
than from the psychological point of view. Indeed it must be confessed
that, from the latter standpoint, his conception of instinct as a
"mental faculty" which "impels" an animal to the performance of
certain actions, scarcely affords a satisfactory basis for genetic
treatment. To carry out the spirit of Darwin's teaching it is
necessary to link more closely biological and psychological evolution.
The first step towards this is to interpret the phenomena of
instinctive behaviour in terms of stimulation and response. It may be
well to take a particular case. Swimming on the part of a duckling is,
from the biological point of view, a typical example of instinctive
behaviour. Gently lower a recently hatched bird into water:
coordinated movements of the limbs follow in rhythmical sequence. The
behaviour is new to the individual though it is no doubt closely
related to that of walking, which is no less instinctive. There is a
group of stimuli afforded by the "presentation" which results from
partial immersion: upon this there follows as a complex response an
application of the functional activities in swimming; the sequence of
adaptive application on the appropriate presentation is determined by
racial preparation. We know, it is true, but little of the
physiological details of what takes place in the central nervous
system; but in broad outline the nature of the organic mechanism and
the manner of its functioning may at least be provisionally
conjectured in the present state of physiological knowledge. Similarly
in the case of the pecking of newly-hatched chicks; there is a visual
presentation, there is probably a cooeperating group of stimuli from
the alimentary tract in need of food, there is an adaptive application
of the activities in a definite mode of behaviour. Like data are
afforded in a great number of cases of instinctive procedure,
sometimes occurring very early in life, not infrequently deferred
until the organism is more fully developed, but all of them dependent
upon racial preparation. No doubt there is some range of variation in
the behaviour, just such variation as the theory of natural selection
demands. But there can be no question that the higher animals inherit
a bodily organisation and a nervous system, the functional working of
which gives rise to those inherited modes of behaviour which are
termed instinctive.
It is to be noted that the term "instinctive" is here employed in the
adjectival form as a descriptive heading under which may be grouped
many and various modes of behaviour due to racial preparation. We
speak of these as inherited; but in strictness what is transmitted
through heredity is the complex of anatomical and physiological
conditions under which, in appropriate circumstances, the organism so
behaves. So far the term "instinctive" has a restricted biological
connotation in terms of behaviour. But the connecting link between
biological evolution and psychological evolution is to be sought,--as
Darwin fully realised,--in the phenomena of instinct, broadly
considered. The term "instinctive" has also a psychological
connotation. What is that connotation?
Let us take the case of the swimming duckling or the pecking chick,
and fix our attention on the first instinctive performance. Grant that
just as there is, strictly speaking, no inherited behaviour, but only
the conditions which render such behaviour under appropriate
circumstances possible; so too there is no inherited experience, but
only the conditions which render such experience possible; then the
cerebral conditions in both cases are the same. The biological
behaviour-complex, including the total stimulation and the total
response with the intervening or resultant processes in the sensorium,
is accompanied by an experience-complex including the initial
stimulation-consciousness and resulting response-consciousness. In the
experience-complex are comprised data which in psychological analysis
are grouped under the headings of cognition, affective tone and
conation. But the complex is probably experienced as an unanalysed
whole. If then we use the term "instinctive" so as to comprise all
congenital modes of behaviour which contribute to experience, we are
in a position to grasp the view that the net result in consciousness
constitutes what we may term the primary tissue of experience. To the
development of this experience each instinctive act contributes. The
nature and manner of organisation of this primary tissue of experience
are dependent on inherited biological aptitudes; but they are from the
outset onwards subject to secondary development dependent on acquired
aptitudes. Biological values are supplemented by psychological values
in terms of satisfaction or the reverse.
In our study of instinct we have to select some particular phase of
animal behaviour and isolate it so far as is possible from the life of
which it is a part. But the animal is a going concern, restlessly
active in many ways. Many instinctive performances, as Darwin pointed
out,[166] are serial in their nature. But the whole of active life is
a serial and coordinated business. The particular instinctive
performance is only an episode in a life-history, and every mode of
behaviour is more or less closely correlated with other modes. This
coordination of behaviour is accompanied by a correlation of the modes
of primary experience. We may classify the instinctive modes of
behaviour and their accompanying modes of instinctive experience under
as many heads as may be convenient for our purposes of interpretation,
and label them instincts of self-preservation, of pugnacity, of
acquisition, the reproductive instincts, the parental instincts, and
so forth. An instinct, in this sense of the term (for example the
parental instinct), may be described as a specialised part of the
primary tissue of experience differentiated in relation to some
definite biological end. Under such an instinct will fall a large
number of particular and often well-defined modes of behaviour, each
with its own peculiar mode of experience.