Page sixteen 



E^OLUTION 



June, 1930 



dom, as it were — that is, witiiout reference to the 

 effect that would be produced, a-teleologically. Sup- 

 pose 3'ou prod the innards of a watch at random — 

 bring about some alteration in ignorance of the 

 effect it may have. Are you likely to make it a 

 better-running watch? A change, purely accident- 

 al in this sense, wrought in any complicated organ- 

 ization is more likely to injure or wreck than to 

 improve that organization for the specific func- 

 tion (in the case of life, multiplication) which it 

 subserves. But, unless the organization has readied 

 its absolute maximum of efficiency already, there 

 will still remain some changes, and therefore some 

 random changes, that will help. And so, occasional- 

 ly, when your watch has stopped or is running poor- 

 ly, you may knock it, prod it, or drop it, and find 

 that, by the lucky replacement of a cog, or the 

 displacement of a sand grain, it starts up meri'ily 

 again. We shall return to this topic later. Mean- 

 while, we stand on our data : despite the stagger- 

 ing complexity of adaptation in living things, the 

 vast majority of mutations are, as is to be expected, 

 anti-adaptive. 



What Causes Mutations? 



It will not suffice, however, simply to call the 

 changes "accidental." An accident is something 

 whose cause was independent of something else you 

 are interested in, but every accident has its cause 

 just the same. And so we return again to our per- 

 ennial question: What is the cause of mutations.'' 

 Evidently, we may now say, not any outer or 

 inner tendency toward perfection of the life force, 

 but that does not help us very much, scientifically. 

 The mutations whose origination has been known to 

 geneticists have been on the whole very scattered 

 and sporadic, so that little of definite information 

 could be obtained, by collecting these observations 

 concerning the conditions which may have been con- 

 tributory to their occurrence. The trouble was that 

 mutations having a conspicuous visible effect are 

 so very rare anyway that one does not find enough 

 in any one experiment to "count." However, the 

 very negativeness of this result, and the varied 

 character of the mutations as they did occur, sug- 

 gested that their occurrence had little or no re- 

 lation to the ordinary variables of the environment. 



Efforts have been by no means lacking, on the 

 part of numerous investigators, to find the cause, 

 or a cause, of visible mutations, by trying all sorts 

 of maltreatments in the attempts to j^roduce such 

 changes. In the course of this work, animals and 

 plants have been drugged, poisoned, intoxicated, 

 etherized, illuminated, kept in darkness, half-smoth- 

 ered, painted inside and out, whirled round and 

 round, shaken violently, vaccinated, mutilated, edu- 

 cated and berated with everything except affection, 

 from generation to generation But their genes 

 seemed to remain oblivious, and they could not be 

 distracted into making an obvious mistake in the re- 

 production of daughter genes just like themselves. 



Tlie new genes were exact duplicates of the old 

 ones, showing no demonstrable mutations, or at 

 most such a scattering few as might have occurred 

 anyliow. : 



And yet mutations certainly do happen, even 

 though rarely. In the examination of over twenty 

 million fruit-flies, not specifically maltreated, over 

 four liundred visible mutations have been found. 

 These mutations must have causes. What then 

 can the causes be.'' What subtle conditions are they, 

 apparently so independent even of violent injury 

 and of other drastic and obvious changes in the 

 physiological or pathological state of the organism.' 

 In going over the data on mutational occurrences 

 in Dfosophila the present writer in 1920 reported 

 the finding of evidence that in this fly, when a mu- 

 tation occurred in a given gene of a cell, not only ■ 

 (lid the hundreds or thousands of genes of other 

 kinds in that cell remain unchanged, but even the 

 twin gene of the other set in the same cell — i.e., 

 the originally identical gene that the individual 

 had received from its other parent — remained un- 

 changed also. Here, then, are two genes of identi- 

 cal chemical composition, lying very close to one 

 anotlier in the same cell — on the average less than a 

 thousandth of a millimeter apart — and one of 

 them is caused to mutate but its duplicate is not. 

 Neither do tlie identical genes in neighboring cells 

 mutate. Evidence for this same kind of occurrence 

 has been adduced in other organisms. Why do not i 

 the same general conditions, acting on the same 

 materials, produce everywhere the same results.'' If 

 events in this sphere are apparently so indetermin- 

 istic, is it any wonder that we could not in our pre- 

 vious trials, by the application of definite condi- 

 tions, produce definite mutational results.'' 



Must Explore Newly Found World of the Little 

 For Mutation Cause 



In view of tiiese accumulating findings, the con- 

 clusion seemed to me to become increasingly prob- 

 able, not that mutations were causeless, or expres- 

 sions of "the natural cussedness of things," or of 

 the devil, but that, as Troland had suggested prior 

 to the finding of this evidence, they were not ordi- 

 narily due directly to gross or molar causes, but 

 must be regarded as the results of individual ultra- 

 microscopic accidents — events too far removed from 

 us in fineness to be readily susceptible to any exact 

 control on our part. In other words, an appeal 

 was made to the newly found world of the little 

 which the old-line biologist and philosopher do not 

 take sufficiently into consideration. 



The genes are not only protected by a cell mem- ^^ 

 brane but by a nuclear membrane inside of that, 

 and possibly again by a chromosomal envelope of 

 some kind ; they may be well sliielded, therefore, 

 from the reach of any poisonous substances or un- 

 usual products of metabolism. Tliey can not, how- 

 ever, escape the interplay of the helter-skelter mole- 

 cular, atomic and electronic motions that are con- 



