302 
NATURE 
[JULY 24, 1902 
This disarrangement and constant rearrangement of the sensa- 
tions, or impressions from sensations, which we gather, so that 
their connections in time are altered, seems to me the most fun- 
damental and essential characteristic of consciousness which we 
know. It is not improbable that hereafter it will become pos- 
sible to give a better characterisation of consciousness. In that 
case the opinion just given may become unsatisfactory and have 
to yield to one based on greater knowledge. - The characteristic 
we are considering is certainly important, and so far as the 
available evidence goes it belongs exclusively to consciousness. 
Without it life would have no interest, for there would be no 
possibility of experience, no possibility of education, 
Now the more we have learned about animals, the better have 
we appreciated the fact that in them only such structures and 
functions are preserved as are useful or have a teleological 
value. Formerly a good many organs were called rudimentary or 
vestigial, and were supposed to be useless survivals because they 
had no known function. But in many cases the functions have 
since been discovered. Such, for example, were the pineal 
gland, the pituitary body, the suprarenal capsules and the 
Wolffian body of man, all of which are now recognised to be 
functionally important structures. Useless structures are so 
rare that one questions whether any exist at all, except on an 
almost insignificant scale. It has accordingly become well-nigh 
impossible for us to imagine consciousness to have been evolved, 
as it has been, unless it had been bionomically useful. Let us, 
therefore, next consider the value of consciousness from the 
standpoint of bionomics.! 
We must begin with a consideration of the nature of sensa- 
tions and the object of the reactions which they cause. In the 
simpler forms of nervous action a force, usually, but not neces- 
sarily, external to the organism, acts as a stimulus, which causes 
an irritation ; the irritation produces a reaction. Within the 
ordinary range of the stimuli to which an organism is subjected 
the reaction is teleological—that is, it tends to the benefit of the 
organism. A familiar illustration is the presence of food in the 
stomach, which produces a stimulus, the reaction to which is 
manifested by the secretion of the digestive fluid for the purpose 
of digesting the food. An organism might conceivably be main- 
tained solely by this mechanism, in cooperation with the physical 
laws, which govern all matter. Life in such an organism would 
be a succession of teleological processes, essentially mechanical 
and regulated automatically by the organism. By far the 
majority of biologists regard plants as essentially conforming to 
this type of life. Whether they absolutely so conform we do 
not, of course, yet know. 
A sensation involves the interpolation of consciousness be- 
tween the stimulation and the reaction, and in consequence there 
is established the possibility of a higher order of adjustment to 
the external world than can be attained through the teleological 
reaction to a stimulus. This possibility depends upon the fact 
that the intervention of . consciousness permits an adjust- 
ment in accordance, not merely with the immediate sen- 
sation, but also and at the same time in accordance 
with earlier sensations. Thus, for example, the child sees 
an object, and its reaction is to take hold of the object, 
which is hot and hurts the child. Later the child sees 
the object again, and its natural reaction is to take hold of it | 
again ; but the child now reacts differently because its con- 
sciousness utilises the earlier as well as the present sensation ; 
the previous sensation is dislocated in time and fused with the 
present sensation, and a new reaction follows. No argument is 
necessary to establish the obvious conclusion that an organism 
which has consciousness has an immensely increased scope for 
its adjustments to the external conditions ; in other words, con- 
sciousness has a very high value for the organism. It is 
unnecessary to dwell upon this conclusion, for it will be ad- 
helpful or hurtful, and so we regulate our conduct. Objectively 
red, yellow and green do not exist. Similarly with the vibrations 
of the air, certain of which cause the sensation of sound, which 
is purely subjective. But the sound gives us information con- 
cerning our surroundings which we utilise for our teleological 
needs, although in nature, external to us, there is no sound at 
all. Similarly, all our other senses report to us circumstances and 
conditions, but always the report is unlike the external reality. 
Our sensations are symbols merely, not images. They are, 
however, bionomically sufficient because they are constant. 
They are useful, not because they copy the external reality or 
represent it, but because, being constant resulis of external 
causes, they enable consciousness to prophesy or foresee the 
results of the reactions of the organism, and to maintain and 
improve the continual adjustment to the external reality. 
The metaphysicians have for centuries debated whether there 
is any external objective reality. Is it too much to say that the 
biological study of consciousness settles the debate in favour of 
the view that the objective world is real? 
Consciousness is not only screened from the objective world 
from which it receives all its sensations, but also equally from 
immediate knowledge of the body, through which it acts. As I 
write this sentence I utilise vaso-motor nerves, regulating the 
cerebral blood currents, and other nerves, which make my hand 
muscles contract and relax, but of all this physiological work 
my consciousness knows nothing, though it commands the work 
to be done. The contents of consciousness are as unlike what 
is borne out from it as they are unlike what is borne in to it, 
The peculiar untruthfulness to the objective, which conscious- 
ness exhibits in what it gets and gives, would be perplexing 
Were it not that we have learned to recognise in consciousness a 
device to secure better adjustment to external reality. For this 
service the system of symbols is successful, and we have no 
ground for supposing that the service would be better if 
consciousness possessed direct images or copies instead of 
symbols of the objective world. 
Our sensory and motor! organs are the servants of conscious- 
ness, its messengers or scouts, its agents or labourers, and the 
nervous system is its administrative office. A large part of our 
anatomical characteristics exists for the purpose of increasing 
the resources of consciousness, so that it may do its bionomic 
function with greater efficiency. Our eyes, ears, taste, &c., 
are valuable because they supply consciousness with data ; our 
nerves, muscles, bones, &c., are valuable because they enable 
consciousness to effect the needed reactions. 
Let us now turn our attention to the problem of consciousness 
in animals. The comparative method has an importance in 
biology which it has in no other science, for life exists in many 
forms, which we commonly call species. Species, as I once 
heard it stated, differ from one another with resemblance. The 
difference which resembles we term an homology. Our arm, 
the bird’s wing, the lizard’s front leg are homologous. The 
conception of homology, both of structure and of function, lies 
at the basis of all biological science, which must be and remain 
incomprehensible to any mind not thoroughly imbued with this 
conception. Only those who are deficient in this respect can 
fail to understand that the evidence is overwhelming that 
animals have a consciousness homologous with the human 
consciousness. The proof is conclusive. As regards at least 
mammals, I think we could safely say as regards vertebrates, 
the proof is the whole sum of our knowledge of the structure, 
functions and life of these animals. 
As we descend the animal scale to lower forms there is no 
break, and therefore no point, in the descent where we can say, 
here animal consciousness ends and animals below are without 
it. It seems inevitable, therefore, to admit that consciousness 
| extends far down through the animal kingdom, certainly at 
mitted by everyone, except, perhaps, those who start with | 
the @ frzoré conviction that consciousness is an epiphenomenon. 
A sensation gives information concerning the external world. 
Perhaps science has achieved nothing else which has done so 
much to clarify philosophy as the demonstration that the objective 
phenomena are wholly unlike the subjective sensations. Light 
1s a series of undulations, but we do not perceive the undulations 
as such, but as red, yellow and green, or, as we say, colours ; the 
colours give us available information, and we use them as so | 
many labels, and we learn that reactions to these labels may be 
1A convenient term, recently gaining favour, for what might otherwise 
be called the economics of the living organism. Bionomics seems preferable 
to ecology, which some writers are adopting from the German. 
NO. 1708, VOL. 66] 
least as far down as there are animals with sense organs or even 
the most rudimentary nervous system. It is unsatisfactory to 
rely chiefly on the anatomical evidence for the answer to our 
query. We await eagerly results from psychological experi- 
ments on the lower invertebrates. A sense organ, however, 
implies consciousness, and since such organs occur among 
coelenterates we are led to assign consciousness to these 
animals. 
The series of considerations which we have had before us lead 
directly to the conclusion that the development and improve- 
ment of consciousness has been the most important—really the 
dominant—factor in the evolution of the animal series. The 
1 And other organs in efferent relations to consciousness. 
