378 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: 
“Tt appears, as I have already said, that tine 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 influences, 
became preserved and were propagated by heredity (généra- 
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 
