404 



NATURE 



[November 24, 192 1 



Some Problems in Evolution.^ 

 By Prof. Edwin S. Goodrich, F.R.S. 



j T was nearly one hundred years ago that Charles 

 •*• Darwin Degan his scientihc studies in the 

 University of hdinburg-h. No more litting sub- 

 ject, 1 think,, could be found for an address than 

 certain problems relating to his doctrine of evolu- 

 tion. Perhaps the best way of treating these 

 general subjects is by trying to answer some 

 definite questions, l' or instance, we may ask : 

 " Why are some characters inherited and others 

 not? " By characters we mean all those qualities 

 and properties possessed by the organism, and by 

 the enumeration of which we describe it : its 

 weight, size, shape, colour, its structure, com- 

 position, and activities. Next, what do we mean 

 by "inherited"? It is most important, if pos- 

 sible, clearly to define this term, since much of 

 the controversy in writings on evolution is due 

 to its use by various authors with a very different 

 significance — sometimes as mere reappearance, at 

 other times as actual transmission or transference 

 from one generation to the next. Now, I propose 

 to use the word inheritance merely to signify the 

 reappearance in the offspring of a character pos- 

 sessed by the ancestor^a fact which may be 

 observed and described, regardless of any theory 

 as to its cause. Our question, then, is: "Why 

 do some characters reappear in the offspring and 

 others not? " 



It is sometimes asserted that old-estabUshed 

 characters are inherited, and that newly -begotten 

 ones are not, or are less constant, in their re- 

 appearance. This statement will not bear critical 

 examination. For, on one hand, it has been 

 conclusively shown by experimental breeding that 

 the newest characters may be inherited as con- 

 stantly as the most ancient, provided they are 

 possessed by both parents. 2 While, on the other 

 hand, few characters in plants can be older than 

 the green colour due to chlorophyll, yet it is suffi- 

 cient to cut oft' the fight from a germinating seed 

 for the greenness to fail to appear. Again, ever 

 since Devonian times vertebrates have inherited 

 paired eyes; yet, as Prof. Stockard has shown, 

 if a little magTiesium chloride is added to the sea- 

 water in which the eggs of the fish Fundulus are 

 developing, they will give, rise to embryos with 

 one median Cyclopean eye ! Nor is the suggestion 

 any happier that the, so to speak, more deep- 

 seated and fundamental characters are more con- 

 stantly inherited than the trivial or superficial. A 

 glance at organisms around us, or the slightest 

 experimental trial, soon convinces us that the 

 apparently least-important character may re- 

 appear as constantly as the most fundamental. 

 But while an organism may live without some 

 trivial character, it can rarely do so when a funda- 



^ Abridged from the presidenMal address delivered to Section D (Zoology) 

 of the British Association at Edinburgh on September 8. 



2 We purposely set aside complications due to hybridisation and Mendelian 

 segregation, which do not directly bear on the questions at issue, 



NO. 2717, VOL. 108] 



mental character is absent, hence such incomplete 

 individuals are seldom met in Nature. 



Yet undoubtedly some characters reappear with- 

 out fail and others do not. If it is neither age 

 nor importance, what is it that determines their 

 inheritance? Ihe answer is that for a character 

 to reappear in the offspring it is essential that the 

 germinal factors and the environmental conditions 

 which co-operated in its formation in the ancestor 

 should both be present. Inheritance depends on 

 this condition being fulfilled. For all characters 

 are of the nature of responses to environment ^ ;, 

 they are the products or results of the interaction 

 between the factors of inheritance (germinal 

 factors) and the surrounding conditions or stimuli. 

 This power of response or reaction is no mysteri- 

 ous property of organisms — it is the effect pro- 

 duced, the disturbance brought about by the 

 application of a stimulus. All the special 

 properties and activities of living organisms 

 utimately depend on their metaboUsm, of 

 which growth and reproduction are the 

 chief manifestations. The course of meta- 

 bolism, and, consequently, the development in the 

 individual of a character, is moulded or con- 

 ditioned by the environmental stimuli under which 

 it takes place. On the other hand, the living sub- 

 stance, protoplasm, which is undergoing meta- 

 bolism is the material basis of the organism. It 

 has a specific composition and structure peculiar 

 to the particular kind of organism concerned, and 

 this is handed on to the offspring in the germ- 

 cells from which starts the new generation. The 

 inheritance of a character is due, then, not only, 

 to the actual transmission or transference of this 

 specific "germ-plasm" containing the same 

 factors of inheritance (germinal factors) as those 

 from which the parent developed, but also to this 

 factorial complex developing under the same con- 

 ditions (environmental stimuli), as those under 

 which the parent developed. Any alteration either 

 in the effective environmental stimuli or in the^ 

 germinal factors will produce a new result, will| 

 give rise to a new character, will cause the oldl 

 character to appear no longer. 



Now what is actually transmitted from onel 

 generation to the next is the complex of germinalj 

 factors. Hence we should carefully distinguishj 

 between transmission and inheritance. Much of j 

 the endless confusion and interminable contro- 

 versies about the inheritance of so-calledl 

 "acquired characters" is due to the neglect of 

 this important distinction. For it is quite clear] 

 that whereas factors may be transmitted, char- 

 acters as such never are. The characters of the' 

 adult, being responses, are not present as such 



3 In a letter to Nature Sir Ray Lankester long ago directed attention to 

 the importance of ihis consiiieration when discussmg inheritance. He a so 

 pointed out that Lamarck's first law, that a new stimulus alters the charac- 

 ters of an organism, contradicts his second law, that the effects of previous 

 stimuli are fixed by inheritance. (Naturk, vol. 51, 7894.) 



