Theories about emotions stretch back at least as far as the Stoics of ancient Greece – but to date, no definitive taxonomy of emotions exists. Though many have been proposed. And many of the explanations about the apparent biological necessity for some of the emotions (e.g. 'boredom' or 'shyness or 'embarrassment') remain sketchy and controversial.

See :Wikipedia

A (partial) list of 'relatively brief conscious experiences characterized by intense mental activity and a high degree of pleasure or displeasure' (i.e. emotions) include:

• Affection • Anger • Angst • Anguish • Annoyance • Anticipation • Anxiety • Apathy • Arousal • Awe • Boredom • Confidence • Contempt • Contentment • Courage • Curiosity • Depression • Desire • Despair • Disappointment • Disgust • Distrust • Ecstasy • 'Elevation' • Embarrassment • Empathy • Envy • Euphoria • Fear • Frustration • Gratitude • Grief • Guilt • Happiness • Hatred • Hope • Horror • Hostility • Humiliation • Hysteria • Impatience • Jealousy • Loneliness • Love • Lust • Outrage • Panic • Passion • Pity • Pleasure • Pride • Rage • Regret • Remorse • Resentment • Sadness • Saudade • Schadenfreude • Self-confidence • Shame • Shock • Shyness • Sorrow • Suffering • Surprise • Trust • Wonder • Worry.

And there are still more suggestions. A proposal to include 'Interest' was published in the academic journal dedicated to the subject, titled Emotion (published by the American Psychological Association.)

Further, the evolutionary pressures which presumably led to the development and maintenance of emotions, remain unclear. Especially as some would seem only to have negative consequences for the individuals concerned - and for society as a whole.

The neurological and physiological processes for many emotions are completely unknown, and the brain regions which have been identified as playing a role in some (e.g. anger) appear do so by mechanisms (e.g. hormonal) which are only partially explained.