! ah PRESIDENTIAL ADDRESS. 579 
events taking place around the individual : it is the evolution of the cortex which 
makes possible this wide association of sounds and ideas, and this learning by 
experience that is important, rather than the mere instrument which regulates 
the emission of sounds that we learn to associate each with its appropriate idea. 
Charles Darwin recognised this fact quite definitely, and expressed it with his 
usual directness,® when he said, ‘It is not the mere articulation which is our 
distinguishing character, for parrots and other birds possess this power. Nor 
is it the mere capacity of connecting definite sounds with definite ideas ; for it is 
certain that some parrots which have been taught to speak connect unerringly 
words with things and persons with events. The lower animals differ from Man 
solely in his almost infinitely larger power of associating together the most 
diversified sounds and ideas; and this obviously depends on the high develop- 
ment of his mental powers.’ 
What I propose to attempt is to put into serial order those vertebrates which 
we have reason to believe are the nearest relatives to Man’s ancestors now avail- 
able for examination, and to determine what outstanding changes in the struc- 
ture of the cerebral hemispheres have taken place at each upward step that may 
help to explain the gradual acquirement of the distinctively human mental 
faculties, which, by immeasurably increasing the power of adaptation to varying 
circumstances and modifying the process of sexual selection, have made Man 
what he is at present. 
A numerous band of zoologists and psychologists have collected a large mass 
of accurate information relating to the behaviour and intelligence of animals, 
with which Darwin, Huxley, Tylor, and many recent writers have familiarised 
students of anthropology. It is not my intention to attempt to summarise or 
deal directly with these problems of comparative psychology. 
But there has been accumulating during the last few years, thanks largely 
to the efforts of Oskar and Cécile Vogt, Karl Brodmann, and many others,’° the 
material which will eventually enable us to correlate these differences in habits 
and behaviour in different mammals with structural differences in their brains; 
and in this Address I propose to discuss with you what light such investigations 
can throw upon the problems of Man’s origin and the evolution of the instrument 
of his intelligence. If in my attempts to interpret the significance of the pro- 
gressive modifications, which we can demonstrate in the brains of the series of 
mammals I have selected, I shall give utterance to the crudest psychological 
conceptions, you must not credit this entirely to my ignorance of the teachings 
of psychology, but partly to the fact that so far we have been able only dimly 
to realise the nature of the processes that are taking place in the cerebral cortex ; 
and it is safer to use the crudest forms of expression, so as not to delude you 
into the belief, which more precise terms might suggest, that our knowledge had 
yet attained to any degree of completeness or exactitude. 
We know something of the differences in behaviour of a series of Primates 
and of the variations in their responses to electrical stimulation of their brains. 
How far can these differences be correlated with structural distinctions in their 
brains? And how far can such information be used to explain the evolution of 
our own brain, which supplies to each of us the only real knowledge of conscious- 
ness we possess? These are the questions that we are striving to answer. 
The class Mammalia, to which Man belongs, is distinguished from all other 
vertebrates by the size and high development of the brain, and by the fact that, 
to a much greater degree than in any other class, a progressive increase in the size 
of the brain, and more especially of the cerebral cortex. becomes imperative in 
each successive epoch if its possessor is to maintain itself in free and open com- 
petition with its fellows. It was the advance in brain structure in far greater 
measure than anything else that determined the evolution of mammals; 7! and it 
® The Descent of Man, p. 130 in the 1901 reprint. 
” ©. and O. Vogt, ‘Zur Kenntnis der elektrisch erregbaren Hirnrinden- 
Gebiete bei den Saugetieren,’ Journ. f. Psych. u. Neur., Bd. VIII., 1907, p. 280. 
K. Brodmann, Vergleichende Lokalisationslehre der Grosshirnrinde, Leipzig, 
1909. 
11 Tn opening the discussion on the ‘ Origin of Mammals’ at the meetings of 
Section TD, last year, I developed this argument (Brit. Assoc. Reports, 1911, 
p. 424). 
PP 2 
