Ruling out Thinking

How important would you think just brain activity for instance was for the evolution of mammals? In regards to life I think it would be staggering. If this behavior was being selected for down to a molecular/cellular level regularly which I think shows then how it played out in phenotypes is very interesting. Just how you as a human may think with a brain, what is the behavior like for say a population of rodents in a forest, if by chance thought is actually occurring in some form pertaining to the rats neurobiology down to a molecular/cellular level.

Basically from a multicellular tone I think I could view say neurons in any particular species as a type of cell working in concert with many others using say genes for instance to spawn phenotypes. So I could view possibly say its evolution in that sense parallel to say a specie? Such as in the evolution of bats, would brain function as modeled by selective pressures continue to hold impact in bat evolution, or could there be radical shifts in the animals behavior in relation to faster changing variables. Such as say some species you find heteropatric speciation occurring, could that entire change in possible evolutionary history pertain mainly to say brain activity in some species as more a phenotype lean or how well can evolutionary genetics in a population sense rule out brain behavior?