Preface 



The papers contained within this volume are the result of a series 

 of lectures held at The University of Michigan in the spring of 1961, 

 under the auspices of its Institute of Science and Technology. 



Of the several areas of inquiry that are germane to an understand- 

 ing of biological phenomena, one of the more challenging is that 

 which attempts to define the factors responsible for the diversification 

 of cellular structure and function. In planning the lectures from which 

 this volume is derived, we felt that examination of the elements lead- 

 ing to the diversification of biological systems from a broad vantage 

 point might yield a degree of synthesis to an area which is fraught 

 with as much variation in its approaches as the systems which it at- 

 tempts to investigate. This volume deals nearly exclusively with the 

 development of heterogeneity at the cellular and subcellular level, for 

 elucidation of the problems involved will come largely from these 

 areas of investigation which are basically biochemical and molecular 

 in their philosophy. 



In pondering the general problem of diversification in biological 

 systems, we arrive at the realization not only that the properties of 

 cells are the result of a long history of organic evolution but also that 

 prebiological evolution has placed basic restrictions upon what cells 

 may become and what they may do. These restrictions, of course, re- 

 late to the properties of the molecules available for biological use. 

 Thus, in any general discussion of diversification, an examination of 

 the origin of organic molecules makes a logical starting point. This is 

 the topic which has been chosen to introduce the subject. From this 

 point an examination of ways in which molecules may interact to 

 yield biologically useful energy needed for cell maintenance may be 

 considered. Perhaps the most informative system in this respect is the 

 evolution of the photosynthetic mechanism. 



Cell diversification depends upon the variety of catalytic and struc- 

 tural proteins from which the cells are fabricated. These aspects of 

 the problem are examined in three chapters dealing with biochemical 



