18 THE MEANING OF EVOLUTION 
ing which he wrote several books describing them, he 
finally published the great work on which his fame 
depends. This was the “Philosophie Zodlogique.”’ 
In this treatise he taught that the animal kingdom is 
a unit and that all its members are blood relations; 
that the members vary with varying conditions; that 
this variation results in continued advance. In all of 
these points Lamarck is at one with modern thought. 
His idea of the method by which the variation comes 
about has been accepted and rejected; modified, re- 
accepted, and again rejected. 
Lamarck’s conception of the cause of progress was 
somewhat as follows: The desire for any action 
on the part of an animal leads to efforts to accom- 
plish that desire. From these efforts came gradually 
the organ and its accompanying powers. With every 
exercise of these powers the organ and its correspond- 
ing function became better developed. Every gain 
either in function or in organ was transmitted to 
those of the next generation, who were thus enabled 
to start where their parents left off. The general 
environment constantly gave the stimuli that led to 
the adaptive changes. 
American zodlogists have been especially inclined 
toward Lamarck’s ideas. Until Weismann startled 
the scientific world with his sharp denial of the pos- 
sibility of transmitting to offspring any growth ac- 
