228 



SCIENCE. 



[N. S. Vol. XXIV, No. 608. 



An important light is thrown on some 

 facts which seem at first sight to favor the 

 Lamarckian hypothesis by the considera- 

 tion that, though an 'acquired' character 

 is not transmitted to offspring as the con- 

 sequence of the action of external agencies 

 determining the 'acquirement/ yet the 

 tendency to react exhibited by the parent 

 is transmitted, and if the tendency is ex- 

 ceptionally great a false suggestion of a 

 Lamarckian inheritance can readily result. 

 This inheritance of 'variation in tendencies 

 to react' has a wide application, and has 

 led me to coin the word 'educability' as 

 mentioned in the section of this address 

 on psychology. 



The principle of physiological selection 

 advocated by Dr. Romanes does not seem 

 to have caused much discussion, and has 

 been unduly neglected by subsequent 

 writers. It was ingenious, and was based 

 on some interesting observations, but has 

 failed to gain support. 



The observations of de Vries— showing 

 that in cultivated varieties of plants a new 

 form will sometimes assert itself suddenly 

 and attain a certain period of dominance, 

 though not having been gradually brought 

 into existence by a slow process of selection 

 — have been considered by him, and by a 

 good many naturalists, as indicating the 

 way in which new species arise in nature. 

 The suggestion is a valuable one if not 

 very novel, but a great deal of observation 

 will -have to be made before it can be ad- 

 mitted as really having a wide bearing 

 upon the origin of species. The same is 

 true of those interesting observations which 

 were first made by Mendel, and have been 

 resuscitated and extended with great labor 

 and ingenuity by recent workers, especially 

 in this country by Bateson and his pupils. 

 If it should prove to be true that varieties 

 when crossed do not, in the course of 

 eventual interbreeding, produce interme- 

 diate forms as hybrids, but that characters 



are either dominant or recessive, and that 

 breeds result having pure unmixed char- 

 acters—we should, in proportion as the 

 Mendelian law is shown to apply to all 

 tissues and organs and to a majority of 

 organisms, have before us a very important 

 and determining principle in all that re- 

 lates to heredity and variation. It remains, 

 however, to be shown how far the Men- 

 delian phenomenon is general. And it is, 

 of course, admitted on all sides that, even 

 w^ere the Mendelian phenomenon general 

 and raised to the rank of a law of heredity, 

 it would not be subversive of Mr. Darwin's 

 generalizations, but probably tend to the 

 more ready application of them to the ex- 

 planation of many difficult cases of the 

 structure and distribution of organisms. 



Two general principles which Mr. Dar- 

 win fully recognized appear to me to de- 

 serve more consideration and more general 

 application to the history of species than 

 he had time to give to them, or than his 

 followers have accorded to them. The first 

 is the great principle of 'correlation of 

 variation,' from which it follows that, 

 while natural selection may be favoring 

 some small and obscure change in an un- 

 seen group of cells— such as digestive, pig- 

 mentary or nervous cells, and that change 

 a change of selective value— there may be, 

 indeed often is, as we know, a correlated 

 or accompanying change in a physiolog- 

 ically related part of far greater magnitude 

 and prominence to the eye of the human 

 onlooker. This accompanying or correlated 

 character has no selective value, is not an 

 adaptation— is, in fact, a necessary but use- 

 less by-product. A list of a few cases of 

 this kind was given by Darwin, but it is 

 most desirable that more should be estab- 

 lished. For they enable us to understand 

 how it is that specific characters, those seen 

 and noted on the surface by systematists, 

 are not in most cases adaptations of select- 

 ive value. They also open a wide vista of 



