its not really a matter of who "discovered" the instinct theory but who PROPOSED the instinct theory is what i think your question is asking in which case i believe the answer--if my memory serves me right-- is William McDougall
Instinct theory is a theory that looks at motivation of people and animals. In instinct theory, behavior is motivated by instinct, which is ingrained in animals to help them survive.
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.
Purpose
Instinct Theory - 2004 was released on: USA: 18 June 2004 (Triggerstreet.com Online Film Festival)
The cast of Instinct Theory - 2004 includes: LeeAnne Hutchison as Woman Adam Rothenberg as Man
Instinct theory
Albert Einstein discovered the theory of relativity
Albert Einstein discovered the theory of relativity
instinct theory
keep oneself safe
The theory of ghosts was discovered on the 6/6/6 of your mother.
Sigmund Freud