colleagues hypothesized this was because the most educated conservatives tend to be more invested in the hierarchical structure of society and in maintaining the inequality of the status quo in society in order to safeguard their status. SDO levels can also shift in response to threats to political party identity, with conservatives responding to party identity threat by increasing SDO levels and liberals responding by lowering them. Culture SDO is typically measured as an individual personality construct. However, cultural forms of SDO have been discovered on the macro level of society. Discrimination, prejudice and stereotyping can occur at various levels of institutions in society, such as transnational corporations, government agencies, schools and criminal justice systems. The basis of this theory of societal level SDO is rooted in evolutionary psychology, which states that humans have an evolved predisposition to express social dominance that is heightened under certain social conditions (such as group status) and is also mediated by factors such as individual personality and temperament. Democratic societies are lower in SDO measures The more that a society encourages citizens to cooperate with others and feel concern for the welfare of others, the lower the SDO in that culture. High levels of national income and empowerment of women are also associated with low national SDO, whereas more traditional societies with lower income, male domination and more closed institutional systems are associated with a higher SDO. Individuals who are socialized within these traditional societies are more likely to internalize gender hierarchies and are less likely to challenge them. Biology and sexual differences The biology of SDO is unknown. Plenty of evidence suggests that men tend to score higher on SDO than women, and this is true across different countries, cultures, age-groups, classes, religions and educational levels, with the difference generally being an average of half a point on the scale.Researchers argue for an 'invariance' in the difference between men and women's SDO; suggesting that even if all other factors were to be controlled for, the difference between men and women's SDO would still remain – this however in some cases has been challenged, although exceptions may be due to complex and highly dependent factors. From an evolutionary and biological perspective SDO facilitates men to be successful in their reproductive strategy through achieving social power and control over other males and becoming desired mating partners for the opposite sex. Males are observed to be