156 



J. D. BERNAL 



have claimed to demonstrate by mathematical arguments that even such a small 

 part of organized nature as a molecule of ribonucleic acid would, if it had to 

 come together by chance from a congeries of atoms, take almost infinitely more 

 time than the presumed age of the universe. I know Professor Haldane [i] has 

 argued that a very unHkely thing is not an impossible thing and that the chance 

 origin of Ufe cannot be altogether neglected, but most of those bringing forward 

 such argimients use them in a purely negative sense. If life could not have come 

 together by pure chance, they argue, then its presence is either an illusion or that 

 life was created and guided at every step by an intelhgent agent or at least by a 

 teleological seeking for perfection. I do not want here to enter into these argu- 

 ments, which are more philosophical than scientific, but I do want to make the 

 point that the problem has been wrongly posed. There is no question, to anyone 

 who has examined the evidence, of the need to explain the origin of life as con- 

 sisting of one decisive step, because it plainly did not originate as such. Even 



Fig. I. Formal scheme of five orders 



of a sequence of inscribed circles. 



Each unit contains three of the order 



beneath it. 



if we carmot as yet precisely determine the stages of biopoesis, their general 

 character is already apparent, as I have attempted to sketch in my other contri- 

 bution. Over and above any hypothesis of stages in time, we have before us in 

 biochemistry and ultra-cytology concrete evidence of a series of grades of struc- 

 ture of increasing complexity. The structures that we observe or study are not 

 arranged in a continuous order but a discontinuous one. 



Each type of structure seems to be composed of units of fairly definite sizes 

 which come together to form another unit on the next level (Fig. i). Take for 

 example a vertebrate striated-muscle cell or fibre, itself a member with thousands 

 of others of a macroscopic muscle (Fig. 2). Leaving aside the cell membrane, 

 nucleus, mitochondria and other organelles, the functional element is the striated 

 muscle fibril. This is composed of some hundred elements, the myomeres, each 

 with its transverse M and Z membranes still of unknown composition and 

 function. Each myomere contains a parallel arrangement of some thousand dis- 

 tinct myosin fibrils, interleaved with actomyosin fibrils. Both fibrils contain 

 some hundred polypeptide chains [2, 3]. The chains are made of specific sequences 

 of amino acids which in turn are made of between ten and thirty atoms. Here 



