DARWINISM 519 
factory answers to most of them, so that now practically 
no scientific man doubts the essential truth of evolution; 
it is the corner stone of all recent science, the foundation 
of all modern thought. 
444. The Modern Problem. But Darwinism left us 
with a very large and very fundamental problem unsolved. 
Upon what materials does natural selection act in the 
formation of species? Obviously the "fittest" survives, 
but what is the origin of the fittest? This problem Darwin- 
ism did not solve. The solution of it is one of the most 
fundamental and important tasks now being undertaken 
by biologists. The most effective attack is by the method 
of experimental evolution, which forms the subject of the 
next chapter. 
