"Evolution Rate is proportional to the environmental change Rate".

WHY SOME SPECIES ARE MORE MODIFIED THAN OTHERS ?

The answer is simple ... because they are in different environments.
Environments change .... and all life that lives in these environments ... changes together.
All life co-evolves with the changing environments.
Some regions are more susceptible to climatic changes than others.
Some species change more than others, starting from a common ancestor.

"The evolution rate is proportional to the environmental change rate".