18 EVOLUTION OF THE HUMAN EYE 



at work producing those changes which ultimately per- 

 mitted, and culminated in the erect carriage. This factor 

 which paved the way, and to which most of the general 

 changes of human and primate bodily conformation are 

 due, was undoubtedly the arboreal habit, the habit of climb- 

 ing and living up trees, instead of dwelling upon the ground 

 beneath. We are too apt to lay too much stress upon man s 

 descent from the branches. It was not coming down the 

 tree that was so important in the evolution of the human 

 stock; it was the climbing up, the first step toward the 

 freedom of the branches, that counted in the progress of 

 the mammalian stock from which man has sprung." 



In this first lecture Dr. Wood Jones confined his obser- 

 vations to the evolution of the reproductive system, but 

 at its close remarked "that every system and every part of 

 man 's body tell the same story." In three lectures delivered 

 the following year he extended the subject, and dealt witli 

 the influence of the arboreal habit in the general evolution 

 of man. It is my purpose in this lecture to discuss its 

 influence in the evolution of the visual organs. 



The life of mammals in their struggle for existence may 

 be compared to a prolonged game of hide-and-seek. Some, 

 like the Rodentia, have found safety by burrowing in the 

 ground; some, like the Cetacea, by adopting aquatic life; 

 some, like the Quadrumana, by climbing up into the trees; 

 and others, like the Ungulata, by living in herds and acquir- 

 ing protective coloration. The adoption of life in herds and 

 protective coloration is a game at which two can play— the 

 attackers and the attacked. Some of the Carnivora hunt 

 in packs, and most of them have acquired colors and markings 

 which serve as effective camouflage in the districts which 

 they inhabit. For this great game of hide-and-seek the 

 sense-organs have become developed to different degrees 



