CHAPTER I 

 INTRODUCTION 



We begin with a drop of viscid protoplasm the reactions of which 

 we do not understand, and we end lost in the delicacy of the structure 

 of the eye and the intricacies of the ten thousand million cells of the 

 human brain. We begin with photosjnithesis in a unicellular plant, or 

 with a change in the viscosity produced by light in the outer layers of 

 the amoeba, and we end with the mystery of human perception. We 

 begin some one or two thousand million years ago in the warm waters of 

 the Archeozoic era and we end with the speculations of tomorrow. And 

 as we travel together tracing the responses of living things to light from 

 the energy liberated by a simple photochemical reaction to the faculty 

 of appreciating and interpreting complex perceptual patterns, neither 

 in fact nor in fiction does a story more fascinating unfold. It is a story 

 which traces a development from a vague sentiency to apperception, 

 from vegetative existence to the acquisition of the power to mould the 

 environment, from passive reactivity to the ability to create history. 

 Nor is there a story more important. Even at the physiological level 

 some 38% of our sensory input is derived from the retinae,^ impulses 

 from which, even in the complete absence of visual stimuli, are largely 

 responsible for maintaining a tonic influence upon the level of 

 spontaneous activity in the brain. ^ From the psychological point of 

 view the importance of vision is still greater. If, indeed, the proper 

 study of mankind is Man, and if (as we must agree) his behaviour and 

 his contact with the outside world are mediated through his senses, 

 what can be more fundamental than the study of the sense which, more 

 than any other, determines his intelligence and regulates his conduct, of 

 the faculty which eventually played the preponderant role in assuring 

 his dominance and determining his physical dexterity and intellectual 

 supremacy ? We are indeed highly visual creatures. 



It would seem appropriate to introduce a book devoted to the evolution of 

 vision with a portrait of charles darwin (1809-1882) (Fig. 1), the great English 

 naturalist who, like Newton in the world of physics, was one of the very few men 

 who revolutionized world thought in the subject on which he worked— and 

 beyond. But Darwin has a special claim to introduce this chapter, for at a time 

 when the conduct of animals was generally ascribed to the existence of vital 

 forces or psychic activities, and when the orientation of plants was thought to 

 be due to the direct influence of physical stimuli such as light and heat upon the 



^ According to the calculations of Bruesch and Arey (J. cx>mp. Neurol., 77, 631, 

 1942). 



2 See Claes [Arch, intern. Physiol., 48, 181, 1939) and many others, admirably 

 summarized in Grauit {Receptors and Sensory Perception, New Haven, 1955). 



3 



