The Origin of Life and the Formation 



and Organizing Functions of Natural 



Membranes 



p. MITCHELL 



Department of Zoology, University of Edinburgh, Scotland 



The speakers in this Symposium are concerned with the description of diiferent 

 aspects of the processes by which Hving organisms, as we know them to-day, 

 came to acquire the qualitatively different properties that distinguish them 

 from the inanimate things of their enviroimient, I shall attempt to consider the 

 mechanism whereby the contact between the organism and its environment is 

 regulated, particularly in relation to the functions of the membranes that form 

 the boundary between the organism and its environment. It will be appreciated 

 that I cannot therefore consider the organism without its environment, and that 

 from a formal point of view the two may be regarded as equivalent phases 

 between which dynamic contact is maintained by the membranes that separate 

 and link them. This circumstance serves at the outset to emphasize the fact that 

 living organisms are distinguished, not by their momentary appearance, but by 

 their behaviour and by their relationship to their environment. 



I assume that we are attempting to show that a Hving organism, described by 

 Haldane [i] as a 'self-perpetuating pattern of chemical reactions' — may evolve 

 from inanimate things by the operation of general physical laws, even if requiring 

 events of rare occurrence at certain stages. Our task is presumably to describe 

 the least improbable course of events, which may be tantamount to describing 

 a spontaneous process or a natural law. The consideration of general principles 

 that might govern the origin and evolution of Uving organisms is made doubly 

 difficult because we know very little either about the chemicals available at the 

 time when the evolutionary process of Uving organisms may be said to have 

 begun, nor do we possess much information about the mechanisms of stabiliza- 

 tion, growth, and reproduction of living organisms as they exist to-day — the 

 latter fact often being overlooked in discussions about the meaning of the word 

 life. 



I shall attempt to describe certain generaUties about the properties of the 

 things of which present-day organisms are made that may help towards the de- 

 finition of our problem. This approach is essentially a logical extension of that 

 adopted by Schrödinger [2] and of Haldane [3], and makes use of the concepts 

 of molecular architecture mainly developed by Linus Pauling that recently led 



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