Before the French revolution... there were three main social classes outside of the Monarchy
When the revolution escalated, the poor and the middle class joined together to overthrow the rich, eliminating the powerful members of the upper class who opposed the revolution!
We're the poor. We're angry at the monarchy for not feeding our families.
We are the middle class. We live more comfortably, but we successfully start the revolution because we want change in our government.
LET THEM EAT CAKE!! We're upper class so the monarchy benefits us!!!! We don't care what those sad peasants or boring middle class has to say. We have power in the government!
The revolution acted as a selective pressure, targeting the upper class.
Unfortunately for the peasants...they did not have the social standing to gain more power after the revolution. Even with the upper class decreased, many of the poor were killed during the revolution because of the increased instability of the country. Thus, being neither poor nor rich was favorable .
I thought this revolution was going to make things better for us...
Our son still died of starvation!
However, the decline in the upper class allowed the middle class to gain more power, so they adapted and took control. Now, France had a democracy, and the prosperous middle class had changed France for the better! The "Natural selection" of the revolution eliminated the monarchy, and damaged the upper and lower class. This is an example of "stabilizing evolution" where the middle (average) group benefits the most!