Think of it as a tune.


You have shown the simple ABABAB progression - when in reality it is far more of an improvisational music jam where you have:

A
B1
B2
B3
B4
A
B1
B3
B5
B2
B5
A
B1 through B99
A


where the "B" portions are - simple life forms eat the planet farts and proliferate and speciate and have almost uncotrolled growth to the limits of the food supply.