534 



SCIENCE 



[N. S. Vol. LIV. No. 1405. 



ser). These no doubt are mere analogies, but 

 they serve. 



In all probability, then, factors of inheri- 

 tance exist, and the fundamental problem of 

 Biology is, how are the factors of an organ- 

 ism changed, or how does it acquire new fac- 

 tors? In spite of its vast importance, it must 

 be confessed that little advance has been made 

 towards the solution of this problem since the 

 time of Darwin, who considered that variation 

 must ultimately be due to the action of the 

 environment. This conclusion is inevitable, 

 since any closed system will reach a state of 

 equilibrium and continue unchanged, unless 

 affected from without. To say that mutations 

 are due to the mixture or reshuffling of pre- 

 existing factors is merely to push the problem 

 a step farther back, for we must still account 

 for their origin and diversity. The same ob- 

 jection applies to the suggestion that the 

 complex of factors alters by the loss of cer- 

 tain of them. To account for the progressive 

 change in the course of evolution of the fac- 

 tors of inheritance and for the building up 

 of the complex it must be supposed that from 

 time to time new factors have been added; it 

 must further be supposed that new substances 

 have entered into the cycle of metabolism, 

 and have been permanently incorporated as 

 self -propagating ingredients entering into last- 

 ing relation with preexisting factors. We 

 are well aware that living protoplasm con- 

 tains molecules of large size and extraordinary 

 complexity, and that it may be urged that by 

 their combination in different ways, or by 

 the mere regrouping of the atoms within them, 

 an almost infinite number of changes may 

 result, more than sufficient to account for 

 the mutations which appear. But this does 

 not account for the building up of the original 

 complex. If it must be admitted that such a 

 building process once occurred, what right 

 have we to suppose that it ceased at a cer- 

 tain period? We are driven, then, to the con- 

 clusion that in the course of evolution new 

 material has been swept from the banks into 

 the stream of germ-plasm. 



If one may be allowed to speculate still 

 further, may it not be supposed that factors 



differ in their stability? — that whereas the 

 more stable are merely bent, so to speak, in 

 this or that direction by the environment, and 

 are capable of returning to their original 

 condition, as a gyroscope may return to its 

 former position when pressure is removed, 

 other less stable factors may be permanently 

 distorted, may have their metabolism per- 

 manently altered, may take up new substance 

 from the vortex, without at the same time 

 upsetting the system of delicate adjustments 

 whereby the organism keeps alive? In some 

 such way we imagine factorial changes to be 

 brought about and mutations to result. 



Let it not be thought for a moment that 

 this admission that factors are alterable opens 

 the door to a Lamarckian interpretation of 

 evolution! According to the Lamarckian doc- 

 trine, at all events in its modern form, a 

 character would be inherited after the re- 

 moval of the stimulus which called it forth in 

 the parent. ISTow of course, a response once 

 made, a character once formed, may persist 

 for longer or shorter time according as it is 

 stable or not; but that it should continue to 

 be produced when the conditions necessary for 

 its production are no longer present is un- 

 thinkable. It may, however, be said that this 

 is to misrepresent the doctrine, and that what 

 is really meant is that the response may so 

 react on and alter the factor as to render 

 it capable of producing the new character un- 

 der the old conditions. But is this interpre- 

 tation any more credible than the first? 



Let us return to the possible alteration of 

 factors by the environment. Unfortunately 

 there is little evidence as yet on this point. 

 In the course of breeding experiments the oc- 

 currence of mutations has repeatedly been 

 observed, but what led to their appearance 

 seems never to have been so clearly estab- 

 lished as to satisfy exacting critics. Quite 

 lately, however. Professor M. F. Guyer, of 

 Wisconsin, has brought forward a most in- 

 teresting case of the apparent alteration at 

 will of a factor or set of factors under defi- 

 nite well-controlled conditions.* You wiU re- 



8 American Naturalist, Vol. LV., 1921 ; Jour, of 

 Exper. Zoology, Vol. XXXI., 1920. 



