326 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
The problem of drought is being rapidly solved by the discovery 
or development of drought resistant races, not only insuring against 
loss from this cause, but also enormously increasing the possible area 
of cultivation. 
The problem of disease has been attacked in the same way, and 
disease resistant races of most of the important crops have been 
developed, much reducing loss from this source. As a result, food 
production is now beginning to overtake population, and we may 
thank the persistent study of evolution for the result. 
To summarize the present situation in reference to evolution, the 
following statements may be made. Biologists are testing the 
earlier conclusions by means of the multiplying facts. They are 
continually discovering factors which complicate the situation. 
They must learn the influence of factors by experimentation. As a 
result the problem of evolution has been discovered to be very com- 
plex, not to be explained so simply as had been supposed, and there- 
fore is still “in the melting pot,” as a distinguished scientist has 
remarked. All this means, however, that although this difficult 
problem has not been solved in all its details, it is still recognized 
by every biological investigator as a problem to be solved. It is 
not the fact of evolution that is being tested, but the explanation 
of evolution. 
