340 



PRESENT PROBLEMS IN EVOLUTION AND HEREDITY. 



It will be seen at ouce that there are a number of distinct questions 

 involved. 



The matter of tirst importance in life is the repetition and preservation 

 of type, the principle which insures the unerring accuracy and precision 

 with which complex organs are built up from the germ cells; the force 

 of regression and the more remote forces of reversion all work in this 

 conservative direction ; the theory of the preservation of these forces in 

 a specific and continuous form of protoplasm is by far the most plausi- 

 ble we can offer at present. 



The matter of second importance, but equally vital to the preserva- 

 tion of races, in the long run, is the formation of new tyjjes adapted to 

 new circumstances of life. I shall now attemi)t to show that the facts 

 of evolution, while not inconsistent with the idea of continuity of the 

 germ plasm, are wholly at variance with the idea of its independence, 

 separation, or isolation from the functions of the body. This can be 

 done by proving, first, that the theory of evolution solely by natural 

 selection of chance favorable variations in the germ i)lasm is inade- 

 (juate; second, that the inheritance of definite changes in the somatic 

 cells is also necessary to explain evolution, and therefore there must 

 exist some form of force or matter which connects the activities of the 

 somatoplasm with those of the germ plasm. 



In the following table are placed some of the facts of human evolu- 

 tion which we have observed in the first lecture, and as they are i)art 

 of inheritance, they also constitute the main external phenomena of 

 heredity : 



Phenomena of heredity. 



Conservative (toward past type). 



Natural. 



a. Repetition of parental type. 



h. llegressiou (in many characters) to 

 contemporary race type. 



c. Reversion (mainly in single cliar;i< - 

 tera) to past race type. 



Progressive (toward future type). 



Fortuitous and in- 

 definite. 



I 

 \'arialiility. 



a. Definite variation in single cliarac- 

 \ ters, by accumulation ;=. 



j I b. Definite variation in many cliara(!- 

 I ters (from contemporary race 



1 1 type). 



What are causes of these various phenomena! 



Factors of evolution. — The term "kinetogenesis" has been applied 

 to the modern form of the Lamarckiau theory, fi)r it is an application of 

 kinetic or mechanical principles to the origin of all structures such as 

 teeth, bone, and muscle. It would be fatal to this theory if it could be 

 shown that the changes taking place in course of a normal individual 

 life, under the laws of use and disuse, are inadaptive, or do not corre- 

 spond to those observed in the evolution of the race. 



The relative growth of Organs. — Ball,* in his long argument 

 against Lamarckianism, claims that such is the case, and that use 



" Op. cit., p. 129. 



