In what two ways did John Garcia's research challenge the traditional principles of classical conditioning?

John Garcia was an American psychologist very well-known for his researches that focused on taste aversion in rats and for discovering conditioning taste aversion. Taste aversion is often developed after having a drink or food that causes nausea, vomiting or sickness afterwards. Garcia challenged the idea that:

- any association can be learned equally well.

- conditioning takes place in an even faster and stronger manner when the conditioned stimulus is ecologically relevant.

Therefore, the ability to develop a taste aversion works as a survival mechanism. And, regardless of the taste of the food, sights and sounds, ones can tricky themselves into not liking the taste simply because they relate sickness with it.