CONCLUSION 321 
from time to time, each at a single step, from pre- 
existing species. Upon the material thus supplied 
natural selection operates ; the weaker go to the wall, 
the stronger survive. This is also, in all probability, 
the way in which adaptations have arisen. Creatures 
which came into existence displaying a particular new 
structure, which happened to be fitted for a particular 
new function or suited to a particular niche in Nature, 
survived and flourished exceedingly. Those in which 
undesirable organs appeared perished and were no 
more seen. To take Aristotle’s example. If a man 
were to be born with molars in front and incisors at 
the back of his jaw he would die—at least, in the days 
before dentistry. Having his teeth in the positions 
in which they actually stand (although not for this 
reason only), he survives and rules the world. 
After all, the difference between the point of view 
thus briefly indicated, and that of Darwin as expressed 
in the -‘ Origin of Species,’ is only one of detail—of 
detail as to the particular sort of variations by which 
evolution chiefly proceeds. Darwin’s analogy between 
the origin of species in Nature and the origin of races 
under cultivation may be repeated with emphasis, 
although Huxley’s famous criticism, to the effect that 
races which are sterile together have not arisen in 
cultivation, is not yet completely answered. But 
this renders the discontinuous origin of such sterility 
only the more likely ; and when we recall the Mendelian 
behaviour of such characters as long and short style in 
the primrose, or sterility of the anthers in the sweet- 
pea, the solution of the problem does not seem very 
far to seek. 
21 
