I'm not sure if you are aware of this or not: www.artmarcovici.com/rat-traders
Also, I believe it's implicit in parent's post that evolution would produce more rats whose behaviour increases their likelihood of survival. The rats don't need to understand how their behaviour ensures their survival, or that it can be modelled with game theory, etc.
I am well aware that rats don't have to "understand" these processes. There is a shift in perspective underlying this argument though that doesn't help when discussing whether a rat is capable of recognizing another rat's distress (i.e., empathy) or how it perceives the situation from a subjective point of view.
Do you really think this is the simpler explanation?