Be careful, the shortcut you take between biological evolution and brain mechanism is a bit short.
The way you put "we actively select certain thoughts and feeling to focus on" is a bit awkward... For example, do you "actively select" certain thoughts while you dream? Actually, the brain does not work this way, the simple fact is a thought is not like an organism, it does not die.
You can influence a pattern and create a habit, and make it back and forth... not like biological evolution!
In any case, very interesting post.