People regardless of biological sex may exhibit masculine traits and behavior. This has sparked investigation of the intersection of masculinity with concepts from other fields, such as the social construction of gender difference (prevalent in a number of philosophical and sociological theories). The academic study of masculinity received increased attention during the late 1980s and early 1990s, with the number of courses on the subject in the United States rising from 30 to over 300.
When women’s labor participation increased, there were men who felt less comfortable in their masculinity because it was increasingly difficult for them to reconfirm their status as the breadwinner. Traits traditionally viewed as masculine in Western society include strength, courage, independence, leadership, and assertiveness. Standards of manliness or masculinity vary across different cultures, subcultures, ethnic groups and historical periods. Masculine qualities and roles are considered typical of, appropriate for, and expected of boys and men. Lewis Hine's photo of a power house mechanic working on a steam pump
