GENETICS EST MODERN BIOLOGY — BEADLE 413 



I pointed out that in the Kornberg system with the four nucleotides 

 present, nothing happens unless a primer is added. That is not entirely 

 true. After a delay of some three or four hours something does happen 

 even without a primer. What happens is that a DNA molecule is 

 spontaneously formed. It differs from most naturally occurring DNA 

 in that it contains only two of the four nucleotides. Now if this two- 

 unit co-polymer is used as a primer in a new system, it immediately 

 initiates the synthesis of co-polymers like itself. In other words, it 

 starts replicating. Kemember, it arose spontaneously. If you believe 

 in mutation — and you must if you accept scientific evidence — you 

 must believe that if you start with a two-unit co-polymer and let it 

 undergo successive replications, there will eventually occur a mutation 

 with which a pair of nucleotides will be replaced by the pair origi- 

 nally excluded in the process. This conceivably could have been the 

 origin of the four-unit DNA of all higher organisms. 



Knowing that we now know about living systems — how they repli- 

 cate and how they mutate — we are beginning to know how to control 

 their evolutionary futures. To a considerable extent we now do that 

 with the plants we cultivate and the animals we domesticate. This 

 is, in fact, a standard application of genetics today. We could even 

 go further, for there is no reason why we cannot in the same way direct 

 our own evolutionary futures. I wish to emphasize, however — and 

 emphatically — that toliether we should do this and, if so, hoio^ are 

 not questions science alone can answer. They are for society as a 

 whole to think about. Scientists can say what is possible and perhaps 

 something about what the consequences might be, but they are not 

 justified in going further except as responsible members of society. 



Some of you will, I am sure, rebel against the kind of evolution 

 I've been talking about. You will not like to believe that it all hap- 

 pened "by chance." I wish to repeat that in one sense it is not 

 chance. As I have said, the mutations by which we believe organic 

 evolution to have occurred are no more "chance" reactions than those 

 that occur in the organic chemist's test tube. He puts certain reactants 

 in with the knowledge that an expected reaction will go on. From 

 the beginning of the universe this has been true. In the early stages 

 of organic evolution the probabilities were likely very small in terms 

 of time intervals we are accustomed to think about. But for the time 

 then available, they were almost certainly not small. Quite the 

 contrary ; the probability of evolving some living system was likely 

 high. That evolution would go in a particular direction is a very dif- 

 ferent matter. Thus the a priori probability of evolving man must 

 have been extremely small — for there were an almost infinite number 

 of other possibilities. Even the probability of an organism evolvmg 

 with a nervous system like ours, was, I think, extremely small because 

 of the enormous numbers of alternatives. I am therefore not at all 



