n African-American couple, a Latino couple and a white couple, all with the same income levels, apply for housing loans, yet the minority couples are 82 percent more likely to be rejected than the white couple.

In Britain, a black man and a white man are arrested for committing the same crime. The black man, however, is more likely to be found guilty and to receive a longer prison sentence.

These and many other examples of oppression and discrimination can be explained by a theory called social dominance, say Felicia Pratto, an associate professor of psychology, and co-author Jim Sidanius, in a recent book, Social Dominance: An Intergroup Theory of Social Hierarchy and Oppression (Cambridge University Press, 1999).

Pratto and Sidanius base their theory on the observation that all human societies with surplus wealth are group-based social hierarchies, in which there is a dominant group at the top and one or more subordinate groups at the bottom. The dominant group is characterized by possession and control over a disproportionat ely large share of the material and symbolic goods people desire.

Most forms of group conflict and oppression - from racism to sexism - are manifestations of humans' predisposition toward these social hierarchies, they say.

According to social dominance theory, there are three forms of group-based systems: an age system, a gender system and an empty-set system that consists of arbitrary, socially constructed group distinctions contingent upon situational and historical factors. Examples of empty-set systems are those based on race, ethnicity or social class.

Social dominance theory, which integrates components of psychology, sociology and political science, explores the way psychological, intergroup and institutional processes interact with one another to produce and maintain these group-based, hierarchical social structures.

The theory has examined, for example, how both men's and women's gender roles in the family and in the workplace contribute to male dominance in the political sphere, to warfare, to ethnic oppression and racism, and to gender inequality both inside and outside the home.

"Existing research had provided good clues for understanding inequality, but no analysis was really adequate," says Pratto.

"For example, there's lots of evidence that people who want status and power support discriminatory practices and politicians who enact discriminatory policies. But when group inequality is institutionalized, as it was in South Africa and in many other countries, including our own, individual prejudice can't explain group inequality," she says.

"Working on this theory has been like assembling a giant puzzle, using psychology, cultural ideologies, institutional discrimination, gender, and evolutionary theory and how they fit together to explain persistent group inequality," Pratto says.

In their book, Pratto and Sidanius analyze findings from academic studies of discrimination in North America, Europe, Asia and Africa. They conclude that institutional racism exists in cultures worldwide, in forms such as housing discrimination and longer prison sentences for minority men.

The authors also say that racism is more severely targeted toward subordinate men, whom dominant men may see as potential threats and reproductive rivals. Discrimination against women of any group is endemic to all societies, they argue, and is driven by a desire to control them rather than to harm or destroy them.

Pratto hopes the book will be a step in society's journey toward understanding and eventually overcoming forms of discrimination.

"Inequality is one of the signature characteristics of our species and affects how everybody lives, yet it was largely invisible in the research in my field of social psychology," she says. "If this book on social dominance theory makes people think harder about the fact that they do live in unequal societies and why, it could help them recognize the processes that contribute to inequality, and how they participate in those practices.

"We're going to be better equipped to do something about inequality if we understand how it works than if we pretend it only happens to other people," Pratto says.

Pratto began teaching at UConn in 1998. She previously taught at Stanford University, and received her doctorate in psychology from New York University. Sidanius is on the faculty at the University of California-Los Angeles.

Allison Thompson