Answer:
Instinct theory is a belief in psychology that instinct provides humans with the motivation to do certain actions and behave in a specific manner. Instinct theory was good at explaining why, for example, babies root onto their mother's nipple for milk. However, it didn't have much credence when it came to explaining our other behaviors. Instinct theory has been supplemented by drive-reduction theory, and arousal theory, both of which also try to explain motivation.