332 PRESENT PROBLEMS IN EVOLUTION AND HEREDITY. 



establislied by use and disuse u])on })aiticular structures in the ])areut 

 are in some degree transinitted to the offspring ;iiid thus guide tlu' 

 nuiiu course of variation and adaptation. 



The secoud is that all iiarts of the body are variable, and tliat wher- 

 ever \/ariations take a direction favorabh^ (that is, adaptive) to the sur- 

 vival of the ])ar(Mit they tend to be preserved; where they take the op- 

 posite direction they tend to be eliminated. Thus, in the long run, 

 adaptive variations are accuuiulated and a new type is evolved. 



It is evident at once, from a glance over the facts brought forward 

 in tliis lecture, that the first theory is the sim]dest explanation of these 

 facts ; that us(^ and disuse characterizes all the centers of evolution ; that 

 changesof structure are slowly following our changes of function or habit. 



But Avhile the first explanation is the simplest it by no means fol- 

 lows that it is the true one. In fact, it lauds us in many difticnlties, 

 so that I shall reserve the ])ros aiul cons for my second lecture npon 

 heredity. Tlie Lamarckiaii theory is a sus])iciously simple explana 

 tiou of such complex processes. 



LECTURE II. — THE DIFFICULTIES IN THE HEREDITARY THEORY. 



Nur luuss icli uochmals betonen, (lass uacli lueiuer Auffassuug der Aiifaiig eiiier 

 iieuen KeiliB orbliclier Abweichungen, also audi der Eintritt oiner ueneii Art ohne 

 eiue voTansge.si;m,<ir'ue crwovbeiie Abweichuiig nndpiikbar ist. — VincHow. 



State of opinion . — The above quotation from one of the most eminent 

 autliorities of our times represents the unshaken conviction of a very 

 large class upon one side of the question of transmission of acquired 

 characters, which is met by equally firm conviction upon the other side. 



Herbert Spencer, whose entire system of biology, psychology, and 

 ethics is based upon such transmission, says: "I will only add that, 

 considering the width and depth of the effects which acceptance of one 

 or other of these hypotheses must have on our views of life, mind, morals, 

 and politics, the question Avhich of them is true demands, beyond all 

 other questions whatever, the attention of scientific nuMi." * This shows 

 that Spencer considers the matter still suhjndice, and lest you may think 

 I am bringhig before you an issue in which learning and experience 

 are ranged against ignorance and prejudice, I have taken some i)ains 

 by correspondence with a number of friends abroad to learn tlse pres- 

 ent state of opinion. The two leading English and French authorities 

 ni>on this subject express themselves doubtfully. 



(xalton's mind is still wavering, as in his work of 1S81> he says: 



"I am unprepared to say more than a few words on the obscure, 

 unsettled, and much-discussed subject of the possibility of transmitting 

 acquired faculties. - - - There is very little direct evidence of its 

 infiuence in the course of a single generation, if the i)hrase of 'acquired 

 faculties' is used in perfect strictness and all inheritance is excluded 

 that could be I'eferred to some form of natural selection, or of infection 

 before birth, or of peculiarities of nurture and rearing." t 



*Nin€tecnih Ceniury, 18S9. 



\ Naiural Inheritance, 1889, p. 14. • 



