A Mirror Neuron System might be responsible for understanding the behavior of others — these neurons fire both when the animals acts and when another animal acts. This allows for imitation and empathy.
Social Facilitation refers to the impact of human behavior on the presence of others.
Social behavior is influenced by the constant automatic reaction to and interpretation of our environment

Leadership

Leadership pertains to when someone tries to influence the group as a whole. Leadership is primarily determined by the functions the group needs a leader to fulfill.
A participative style, which attempts to involve all in decision-making, promotes high productivity with good relationships between group members.
A more authoritarian, directive style allows group members less say in decisions and produces equal productivity (provided the leader is present), but tends to lead to poorer relationships and less cooperation.
Laissez-faire leadership, which leaves the group to its own devices, results in lower productivity.

Conformity

Conformity is the act of matching attitudes, beliefs, and behaviors to perceived group norms.
The dissent of even one person reduces conformity in a group.
Compliance refers to a form of conformity wherein one goes along with the majority opinion even if they do not personally agree.
Internalization involves taking on board the opinion of another or of a group. This is strongest when the source is perceived to be an expert.

Obedience refers to complying with the demands of an authority figure
Ordinary people will go very far indeed when they are instructed to do so by someone perceived to be in a position of authority.
- People are more prepared to inflict pain if they can distance themselves from the victim.
- Believing the violence to be a means to an end in a worthy cause (i.e., any form of ideological justification), increases obedience.

Dividing people into ethnic groups, and stereotyping behavior according to group membership may have had evolutionary advantage
Prejudice is a global phenomenon and clearly situational influences contribute to its development
- Personality characteristics, such as being less flexible and more authoritarian, are associated with prejudice
- Prejudice can also arise from a general need to see oneself positively
- Prejudice can also be a form of scapegoating, in which aggression is directed towards an innocent third party
Group Conflict Theory offers an explanation for negative attitudes towards racial integration and efforts to promote diversity—the majority group perceives the minority group(s) to be in competition with the majority group
The absence of direct contact with another group leads to autistic hostility (ignorance of others) which produces a failure to understand the reasons for their actions and provides no opportunities to find out if negative interpretations of their behavior are incorrect.
- Contact between opposing groups is needed before prejudices can be reduced, provided the contact does not reinforce stereotypes or inequities

Coaction Effect - when people are asked not to compete, they work faster when they can see others working.
Audience Effect - people work faster when they are being observed by others.
The Werther Effect - a spike in copycat suicides after a widely publicized suicide. The copycats have similar demographics to the publicized person, and so more of these tend to get reported.
- It is effectively an Information Hazards.
- A manifestation of this — there is a correlation between when a suicide’s publication and the number of fatal accidents (i.e., the drivers were copycats)