Social psychology focuses on social psychologists' interaction with each other and argues that humans are social creatures who are born into families and cultures. Particular areas of interest for social psychologists include studies on conformity and obedience, as well as looking at how a minority group can persuade the majority to change their minds or behaviour. This area of psychology also explores group behaviour, interpersonal attraction, leadership, and explanations of aggression and altruism. Social influence can be defined as "the process whereby attitudes and behaviour are influenced by the real or implied presence of others". Minorities can and do influence majorities as social and scientific innovations clearly demonstrate. Research into social influence raises questions about experimental validity. Psychologists distinguish between internal validity and external validity. Social psychologists face a dilemma when investigating social influence. Preventing psychologists from undertaking any research that might involve stress or conflict would necessarily result in a somewhat "lopsided" view of psychology.