JuLy 24, 1902] 
NATURE 303 
sense organs have been multiplied and perfected in order to 
supply consciousness with a richer, more varied and more trust- 
worthy store of symbols, corresponding to external conditions. 
The nervous system has grown vastly in complexity in order to 
permit a constantly increasing variety in the time dislocations of 
sensations. The motor and allied apparatus have been multiplied 
and perfected in order to supply consciousness with more 
possibilities of adjustment to external reality, which might be 
advantageous. 
If we thus assign to consciousness the leading 7é/e in animal 
evolution we must supplement our hypothesis by another, 
namely, that conscious actions are primary, reflex and instinctive 
actions secondary; or in other words, that for the benefit of the 
organism conscious actions have been transformed into reflexes 
and instincts. Unfortunately, we must rely chiefly on future 
physiological and psychological experiments to determine the 
truth of this hypothesis. Its verification, however, is suggested 
by certain facts in the comparative physiology of the vertebrate 
hervous system, which tend to show that in the lower forms 
(amphibia) a certain degree of consciousness presides over the 
functions of the spinal cord which in mammals is devoted to 
reflex actions. Its verification is further suggested by the natural 
history of habits. As we all know, new actions are performed 
with difficulty, and slowly, but if often repeated they are soon 
easier and more rapid. If a given reaction to a sensation or 
group of sensations through consciousness is advantageous to the 
organism, and the environment is such that the sensation is often 
repeated, then a habit is formed, and the response becomes more 
rapid ; and often in ourselves we see habits, which arose from con- 
scious action, working almost without the participation of con- 
sciousness, and moreover working usefully, because rapidly. The 
usefulness of conscious reactions is that they are determined, not 
merely by the present sensation, but also by past sensations; but 
they have the defect that they are slow. We can readily under- 
stand that it would aid an organism to have the quicker reaction 
substituted, and we thus recognise a valid teleolugical reason for 
the replacement of conscious action by habits in the individual, 
by instincts in the race. The investigation of the evolution of 
reflexes and instincts is one of the important and most promising 
tasks of comparative psychology. 
_A frank, unbiassed study of consciousness must convince every 
biologist that it is one of the fundamental phenomena of at least 
animal life, if not, as is quite possible, ofall life. Nevertheless 
its consideration has barely a place in biological science, although 
it has long occupied a vast place in philosophy and metaphysics. 
If this address should contribute to a clearer appreciation of the 
necessity of treating consciousness as primarily a problem for 
biological research to solve, my purpose will be achieved. In 
an ideal world philosophers and men of science would be iden- 
tical ; in the actual world there are philosophical men of science 
and scientific philosophers ; but in the main the followers of the 
two disciplines pursue paths which are, unfortunately, distinct. 
The philosophical mind is of a type unlike the scientific mind. 
The former tries to progress primarily by thought based on the 
data available, the latter seeks to advance primarily by collecting 
additional data. The consequence of this difference is that 
philosophy is dependent upon the progress of science, but we 
who pursue the scientific way can make no greater mistake than 
to underestimate philosophy. The warning is needed. Data 
of observation are a treasure and very precious. They are the 
foundation of our mental wealth, but that wealth consists of the 
thought into which the data are transmuted. In pleading, 
therefore, for an increased observational study of consciousness 
we plead, not merely for science, but equally for philosophy. The 
scientific progress must come first. Hence we urge the advan- 
tage of investigating consciousness in its immediate revelations, 
which are accessible now. Let us give up the ineffectual struggle 
to discover the essential nature of consciousness until we can 
renew it with much larger resources of knowledge. 
The psychologists ought now to apply the comparative method 
onagrand scale. They are just beginning to use it. Years of 
patient labour must pass by, but the reward will be very great. 
The psychic life of animals must be minutely observed, the 
conditions of observation carefully regulated, and the results 
recorded item by item. The time has passed by for making 
generalisations on the basis of our common, vague and often 
inexact notions concerning the habits of animals. Exact ex- 
perimental evidence will furnish a rich crop of psychological 
discovery. Scientific psychology is the most backward in its 
development of all the great divisions of biology. It needs, 
NO. 1708, VOL. 66] 
however, little courage to prophesy that it will bring forth results 
of momentous importance to mankind. After data have been 
gathered, generalisations will follow which, it may be hoped, 
ya us on to the understanding of even consciousness 
itself, 
The teleological impress is stamped on all life. Vital functions 
have a purpose. The purpose is always the maintenance of the 
individual or of the race in its environment. The entire evolu- 
tion of plants and animals is essentially the evolution of the 
means of adjustment of the organism to external conditions. 
According to the views I have laid before you, consciousness 
is a conspicuous, a commanding factor of adjustment in animals. 
Its superiority is so great that it has been, so to speak, eagerly 
seized upon by natural selection and provided with constantly 
improved instruments to work with. A concrete illustration 
will render the conception clearer. In the lowest animals, the 
coelenterates, in which we can recognise sense organs, the 
structure of them is very simple, and they serve as organs of 
touch and of chemical sensation resembling taste. In certain 
jelly fishes we find added special organs of orientation and 
pigmented spots for the perception of light. In worms we have 
true eyes and vision. In vertebrates we encounter the true 
sense of smell. Fishes cannot hear, but in the higher verte- 
brates, that is from the amphibians up, there are true auditory 
organs. In short, both the senses once evolved are improved 
and also new senses are added. It is perfectly conceivable that 
there should be yet other senses, radically different from any we 
know. Another illustration, and equally forcible, of the evolu- 
tion of aids to consciousness might be drawn from the compara- 
tive history of the motor systems, passing from the simple 
contractile thread to the striated muscle fibre, from the primitive 
diffuse nunculature of a hydroid to the highly specialised and 
correlated muscles of a mammal. 
It is interesting to consider the evolution of adjustment to 
external reality in its broadest features. In the lowest animals 
the range of the possible adjustment is very limited. In them, 
not only is the variety of possible actions small, but they cover 
also a small period of time. In animals which have acquired 
a higher organisation, the adjustments are more complex both 
because the reactions are more varied and because they cover a 
longer period of time. Thus the jelly fish depends upon such 
food as happens to come within its reach, seizing from moment 
to moment that which it encounters ; but a lobster pursues its 
food, making complicated movements in order to reach and seize 
it. One can trap lobsters easily ; I doubt if one could trap a 
jelly fish at all. The next great advance is marked by the 
establishment of communication between individuals of the same 
species. About this phenomenon we know exceedingly little ; the 
investigation of it is one of the most important duties of the 
comparative physiologist. Its bionomic value is obviously great, 
for it allows an individual to utilise the experience of another as 
well as its own. We might, indeed, compare it with the 
addition of a new sense, so greatly does it extend the sources of 
information. The communication between individuals is 
especially characteristic of vertebrates, and in the higher 
members of that subkingdom it plays a very great 7é/e in aiding 
the work of consciousness. In man, owing to articulate speech, 
the factor of communication has acquired a maximum import- 
ance. The value of language, our principal medium of com- 
munication, lies in its aiding the adjustment of the individual 
and the race to external reality. Human evolution is the 
continuation of animal evolution, and in both the dominant 
factor has been the increase of the resources available for con- 
sciousness. 
In practical life it is convenient to distinguish the works of 
nature from the works of man, the ‘‘ natural” from the “ arti- 
ficial.” The biologist, on the contrary, must never allow himself 
to forget that man is a part of nature and that all his works are 
natural works. This is specially important for the present dis- 
cussion, for otherwise we are likely to forget also that man is as 
completely subject to the necessity of adjustment to external 
reality as any other organism. From the biological standpoint, 
all the work of agriculture, of manufactures, of commerce and of 
government is a part of the work of consciousness to secure the 
needed adjustments. All science belongs to the same category 
as the teleological efforts of a jelly fish or lobster. It is work 
done at the command of consciousness to satisfy the needs of 
existence. The lesson of all this to us is that we should 
accustom ourselves to profit by our understanding of the trend 
of evolution, which, in the progress humanity makes, obeys the 
. 
