Carl Jung, a Swiss psychoanalyst, is a researcher who took an etic approach in his studies. Jung studied mythology, religion, ancient rituals, and dreams, leading him to believe that there are archetypes that can be identified and used to categorize people's behaviors. Archetypes are universal structures of the collective unconscious that refer to the inherent way people are predisposed to perceive and process information. The main archetypes that Jung studied were the persona (how people choose to present themselves to the world), the animus/anima (part of people experiencing the world in viewing the opposite sex, that guides how they select their romantic partner), and the shadow (dark side of personalities because people have a concept of evil; well-adjusted people must integrate both good and bad parts of themselves). Jung looked at the role of the mother and deduced that all people have mothers and see their mothers in a similar way; they offer nurture and comfort. His studies also suggest that "infants have evolved to suck milk from the breast, it is also the case that all children have inborn tendencies to react in certain ways." This way of looking at the mother is an etic way of applying a concept cross-culturally and universally.