384 BIOLOGY AND ITS MAKERS 



variation or heredity, they remain basal factors in any theory 

 of evolution. 



Time and Favorable Conditions. — Lamarck supposed a 

 very long time was necessary to bring about the changes which 

 have taken place in animals. The central thought of time 

 and favorable conditions occurs again and again in his 

 writings. The following quotation is interesting as coming 

 from the first announcement of his views in 1800: 



*' It appears, as I have already said, that time and favorable 

 conditions are the two principal means which nature has 

 employed in giving existence to all her productions. We 

 know that for her time has no limit, and that consequently 

 she has it always at her disposal. 



"As to the circumstances of which she has had need and 

 of which she makes use every day in order to cause her pro- 

 ductions to vary, we can say that in a manner they are 

 inexhaustible. 



"The essential ones arising from the influence and from 

 all the environing media, from the diversity of local causes, 

 of habits, of movements, of action, finally of means of living, 

 of preserving their lives, of defending themselves, of mul- 

 tiplying themselves, etc. Moreover, as the result of these 

 different influences, the faculties, developed and strengthened 

 by use, become diversified by the new habits maintained for 

 long ages, and by slow degrees the structure, the consistence — 

 in a word, the nature, the condition of the parts and of the 

 organs consequently participating in all these iniluences, 

 became preserved and were propagated by heredity (genera- 

 tion)." (Packard's translation.) 



Salient Points. — The salient points in Lamarck's theory 

 may be compacted into a single sentence: It is a theory of 

 the evolution of animal life, depending upon variations 

 brought about mainly through use and disuse of parts, 

 and also by responses to external stimuli, and the direct 



