



VOLUTION OF INTELLIGENCE. 119 



vas often scarcely larger than the brain of the gigantic 

 reptiles which preceded them. It need hardly be 

 pointed out that man owes his mastery of the world to 

 brain-power, not brute force. Most of the peculiarities 

 in the structure of the human body are closely related to 

 the immense development of the brain. The size and 

 shape of the brain-case has greatly influenced the de- 

 velopment of the skull ; and even the erect attitude and 

 consequent modifications of the hind limbs, vertebral 

 column, and ether parts are probably an adaptation for 

 supporting the heavy weight of the brain. In other 

 respects the structure of man is not very specialised, and 

 differs but little from that of his nearest allies, the 

 anthropoid apes. 



Evolution from the scientifi point of view, as it ap- 

 pears to an outside observer, may be represented as a 

 vast and continuous series of changes in a continuous 

 stream of living matter. Each stage in the process is 

 determined by that which precedes it, and determines 

 that which follows. The scientific generalisations based 

 on the observation of non-living matter, the "laws" of 

 physics and chemistry, hold good when applied to the 

 changes in living matter. There is no special living 

 element, no mysterious life-force ; but life, scientifically 

 described, is a physico-chemical process taking place in 

 the complex compounds of the ordinary elements which 

 make up the protoplasm of living organisms. Meta- 

 bolism, as this process is called, is due to the instability 

 of these compounds, to the fact that external conditions 

 or stimuli applied to them may alter their structure and 

 composition. All the manifestations of life thus corre- 

 spond to metabolic processes. From the very first 

 origin of living protoplasm there has been an unbroken 

 continuity of living processes and substance. The living 

 organisms of the present day are the descendants of those 

 of the past, and all the various forms of life are but the 

 divergent streams from the original source of metabolism. 



