Life on instinct

To be different from an animal,a man has no stable instinct. In the different Era,people has another desire.One Japanese psychiatrist provided"Human is a broken instinct animal". In short, human desire is a culture itself.
Before the war, famous writer"Takeo,Arishima"proclaim "Life on instinct"He was influenced by Nietzsche's thinking. He ran to adultery.After all , he suicided with other's wife in Japanese way(Shinju心中）.What was his instinct? I can't understand at all.