SELECTED PAPERS 



failed as a rule to leave lasting impressions behind. I said as a rule, 

 because during the past few years a number of exceptions have come 

 to light. Not without a thrill was I confronted, during last year's visit 

 at Harvard University, with the fossil microbes discovered by Tyler 

 and Barghoorn, and whose age has been estimated by these scientists at 

 approximately 2,000,000,000 years. The surprisingly intact forms 

 leave no doubt that this oldest thus far known relict of life already 

 possessed a cellular structure. 



Modern cytological examination has indubitably shown that even 

 the single cell represents a highly organized unit, in which easily re- 

 cognizable structural elements, such as the nucleus, protoplasm, mit- 

 ochondria, and many others, cooperate in a remarkably harmonious 

 manner. 



At first sight one might therefore be inclined to conclude that an 

 evolution of life on earth can have begun only after such a complex 

 living unit had somehow found its way to a sufficiently cool terrestrial 

 surface. But for the true-blooded evolutionist it is tempting to conclude 

 that life will have passed through a pre-cellular phase in which the 

 vital characteristics of the various units were reduced to the bare es- 

 sentials. And this almost selfevidently leads to the question in how far 

 it is conceivable that at some time a spontaneous development may 

 have yielded such primitive expressions of life on an initially lifeless 

 earth. This idea, implying a continuity of living and inanimate matter, 

 seems so daring that one might be inclined to dismiss it instantly; 

 nevertheless, several prominent scientists - I shall but mention the 

 great geneticist, H.J. Muller - have not shrunk from it. They derive 

 their support, at least to a degree that cannot be underrated, from the 

 consideration that for the reconstruction of this developmental process 

 they may avail themselves of a time span of no less than 1,000-2,000 

 million years. And the proud edifice constructed by present-day geol- 

 ogy is, so to speak, one concerted demonstration of the fact that the 

 application of a time-coordinate measured in millions of years renders 

 otherwise unimaginable matters intelligible to the human mind. 



Naturally, a test of the projected problem is beset with great dif- 

 ficulties. Given the absence of visually observable testimonials of life 

 during the earliest period of the earth's history, one can only try to 

 infer what physical and chemical conditions were realized during this 

 epoch, and contemplate the question in how far phenomena may be 



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