That's interesting. But not surprising. I'm commenting on the study which talks about altruistic behaviour based on a fellow rat's smell. That shows not so much compassion, as it shows kin-selection. Your sources show how evolution has favoured rats that are somewhat universally altruistic, i.e. plays a forgiving role in the prisoner's dilemma, and therefore is the prominent behaviour in these rats. While evolution has preferred rats with more altruistic tendencies, and these rats probably have some fairly autonomic emotions that guide them to these behaviours, a rat doesn't process a situation and use its moral compass or show 'compassion' as a human would. That's what I wanted to say.