But doing what is in one's best interest isn't necessarily the more intelligent decision. In a rat society, the more "intelligent" rats can possibly be better at acquiring resources to survive if selective pressure is put upon those with such talents but can just as well be early signifiers of 'behavioral sinks'[0]. Not to mention, certain illnesses, mental and otherwise can change motive regardless of IQ.

Actions don't necessarily dictate intelligence. The goal of life has to be defined to make such arguments. For example, using a maze as an analog you could argue the more intelligent person can arrive to the end faster and more elegantly but with life, it has no such defined and agreed on ends. If we're arguing that selfishness is a sign of intelligence then that view is quite myopic.

[0]: https://en.wikipedia.org/wiki/Behavioral_sink