It seems that any fool can write about evolution as I shall demonstrate:
Consider an entity that makes copies of itself.
Do we now have a population of identical replicators?
Some copies, of course, may meet the complex environment and quickly bite the dust. Some may escape damage and some may be altered. There may be incorrect copies.
The majority of the population may well be identical to the the parent but as waves of copies bounce against the world and are perhaps changed errors may survive and reproduce.
Assuming fairly constant circumstances the original parent and it's clones will churn out product over time with an average reproductive success rate of F, which stands for fitness. Higher F values mean more descendants.
Any variant can only have a value for F that is smaller, larger or the same as the parent.
When altered copies have a nonzero success rate then we should expect the population over time to be dominated by high F variants. This allows for a larger pool of possible variation.
A change in circumstances may favor a low F variant; smaller pools with fewer varieties may not survive a new environment at all.
An inconstant world drives a population with differing strategies.