Much of the time we explain behavior using the nature of the people in question: someone has a ‘bad personality’, or is ‘has a good heart’, is ‘evil’, etc. However, accounts that rely solely on a person’s disposition fail to take into consideration of impact of the social environment…
One of the most famous studies in social psychology investigated the impact of the social situation on prison behavior, testing the dispositional hypothesis: That the supposed nature of the people who populate prisons (both inmates and guards) creates the awful conditions. In the study, participants were *randomly assigned* to the role of either prisoners or guards. The effect of this role over powered the effect of participants’ individual personalities in determining resultant behavior: “Despite the fact that guards and prisoners were free to engage in any form of interaction (positive or negative, supportive or affrontive, etc.), the characteristic nature of their encounters tended to be negative, hostile, affrontive, and dehumanizing” (Haney, Banks, & Zimbardo, 1973, p. 80). This effect was so strong that the study had to be halted prematurely due to ethical considerations.
Zimbardo is still active in pursuing the implications of this line of work, especially as an aid in understanding the scandal involving behavior at Abu Graib in Iraq. You can read a lot more about his work and view a slide show and other media presentations at this website.
Reference
Haney, C., Banks, C., & Zimbardo, P. (1973). Interpersonal dynamics in a simulated prison. International Journal of Criminology and Penology, 1, 69-97.