Ok. you got the one thing. Species are mutable
Now, let us give a senerio.
You have a species that is mutable.. but seperated for some reason.
Each groups of those populations do not interbred with each other, for what ever reason. Each of those groups are mutable.. they change.. gradually.
Now, lets go from all those little tiny baby steps, and go and have many many thousands of little baby steps, but each of those two groups going into a different direction. Sooner or later, those two group can not interbreed. At that point.. guess what. They are different species.
That is what darwin was saying is the 'origin of species'. The fact that populations will be 'mutable' is evolution.
See how simple it is?
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