530 



SCIENCE 



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



wbich may be observed and described, regard- 

 less of any tbeory as to its cause. Our ques- 

 tion, tben, is : " Why do some cbaracters re- 

 appear in the offspring and otbers not ? " 



It is sometimes asserted that old-established 

 characters are inherited, and that newly be- 

 gotten ones are not, or are less constant, in 

 their reappearance. This statement will not 

 bear critical examination. For, on the one 

 hand, it has been conclusively shown by ex- 

 perimental breeding that the newest charac- 

 ters may be inherited as constantly as the 

 most ancient, provided they are possessed by 

 both parents.^ While, on the other band, few 

 'characters in plants can be older than the 

 green color due to chlorophyll, yet it is sufE- 

 •cient to cut off the light from a germinating 

 seed for the greenness to fail to appear. 

 Again, ever since Devonian times vertebrates 

 have inherited paired eyes; yet, as Professor 

 Stockard has shown, if a little magnesium 

 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 

 constantly inherited than the trivial or super- 

 ficial. A glance at organisms around us, or 

 the slightest experimental trial, soon con- 

 vinces us that the apparently least-important 

 character may reappear as constantly as the 

 most fundamental. But while an organism 

 may live without some trivial character, it can 

 rarely do so when a fundamental character 

 is absent, hence such incomplete individuals 

 are seldom met in Nature. 



Yet undoubtedly some characters reappear 

 without fail and others do not. If it is neither 

 age nor importance, what is it that deter- 

 mines their inheritance? The answer is that 

 for a character to reappear in the offspring 

 it is essential that the germinal factors and 

 the environmental conditions which cooperated 

 in its formation in the ancestor should both 

 be present. Inheritance depends on this con- 



2 We purposely set aside complications due to 

 hybridization and Mendelian segregation, which do 

 not directly bear on the questions at issue. 



dition being fulfilled. For all characters are 

 of the nature of responses to environment,' 

 they are the products or results of the inter- 

 action between the factors of inheritance (ger- 

 minal factors) and the surrounding conditions 

 or stimuli. This power of response or reac- 

 tion is no mysterious property of organisms — 

 it is the effect produced, the disturbance 

 brought about by the application of a stimu- 

 lus. All the special properties and activities 

 of living organisms ultimately depend on their 

 metabolism, of which growth and reproduction 

 are the chief manifestations. The course of 

 metabolism, and, consequently, the develop- 

 ment in the individual of a character, is 

 molded or conditioned by the environmental 

 stimuli under which it takes place. On the 

 other hand, the living substance, protoplasm, 

 which is undergoing metabolism, is the ma- 

 terial 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, tben, 

 not only to the actual transmission or trans- 

 ference of this specific " germ-plasm " con- 

 taining the same factors of inheritance (ger- 

 minal factors) as those from which the parent 

 developed, but also to this factorial complex 

 developing under the same conditions (en- 

 vironmental stimuli), as those under whicli 

 the parent developed. Any alteration either 

 in the effective environmental stimuli or in 

 the germinal factors will produce a new re- 

 sult, will give rise to a new character, will 

 cause the old character to api>ear no longer. 

 Now what is actually transmitted from one 

 generation to the next is the complex of ger- 

 minal factors. Hence we should carefully dis- 

 tinguish between transmission and inheritance. 



3 In a letter to Nature Sir Bay Lankester long 

 ago drew attention to the importance of this con- 

 sideration when discussing inheritance. He also 

 pointed out that Lamarck's first law, that a new 

 stimulus alters the characters of an organism, con- 

 tradicts his second law, that the effects of previous 

 stimuli are fixed by inheritance. {Nature, VoL 

 LI., 1894.) 



