EVOLUTION 509 
One of the weaknesses in Lamarck's hypothesis appears 
in his illustration of the snake. If we should grant that 
inheritance of the effects of disuse of the legs might possi- 
bly explain their absence in snakes, still it would not ex- 
plain the origin of the snake's desire to glide. That is, of 
course, as much a characteristic of the snake as the absence 
of legs. 
Other arguments against the validity of Lamarckism 
are : first, that no one has ever been able to prove, by ex- 
periment or otherwise, that the effects of use (the so-called 
FIG. 3880. Jean Baptiste Lamarck (1744-1829). 
" acquired characters") are inheritable, while innumerable 
facts indicate that they are not; second, the hypothesis 
could apply only to the animal kingdom, since plants in 
general have no nervous and muscular activities like those 
of animals. A hypothesis of organic evolution, to be valid, 
must apply equally to both plants and animals. 
3. Darwin's Hypothesis. This will be outlined in the 
next chapter. 
