Evolution is defined by rapid innovation, followed by steep decline, followed 
by a period of stagnation. There is a purpose to this; it is not arbitrary.

The periods of innovation serve to enhance humanity so that they may better
 survive and prosper in the future.

The periods of decline are in place to slowly prepare the species for the long 
dark age ahead, so that their collective consciousness may recall evolutionary 
lessons learned in previous ages.

The stagnation period may not seem to provide much of a purpose, but it does. 
Just as sleep rejuvenates and restores an individual's mental state so that he 
or she may enter the new dawn refreshed, so does each new period of stagnation 
provide a refreshment for our race's collective consciousness.

Through it all, the evolutionary cycles are reassuring; we can be assured that 
no race will ever be completely destroyed: only paused for a brief time, and 
then renewed.