Social identity theory was developed by British social psychologists Henri Tajfel and John Turner in the 1970s. They proposed that individuals define their self-concept based on their identification with social groups.

Social identity theory helps us understand how group membership shapes our behavior, attitudes, and perception of self. It also explains how group identities can create a sense of belonging, boost self-esteem, and foster social cohesion. Additionally, this theory is valuable in explaining intergroup conflict and discrimination.

The four theories of self-identity are self-discrepancy theory, self-complexity theory, self-evaluation maintenance theory, and social identity theory. These theories focus on different aspects of how individuals perceive themselves in relation to others, their own ideals, and the roles they play in social groups.

1. Social identity theory suggests that individuals conform to peer pressure to maintain a positive social identity within a group.
2. Social learning theory proposes that individuals are more likely to adopt behaviors they see being rewarded by their peers.
3. The self-categorization theory suggests that individuals conform to peer pressure to enhance their sense of belonging and similarity to the group.

Social developmental theory is a psychological perspective that explores how social interactions and experiences shape an individual's development over their lifespan. It emphasizes the importance of relationships, culture, and societal influences in shaping an individual's identity, beliefs, and behavior. The theory highlights the impact of social environments on cognitive, emotional, and social development.