Depending on your political viewpoints, the recent passing of Prop 8 in California is either a huge disappointment or sigh of relief. With debate about same-sex marriages fresh in people's minds, I thought I'd discuss some social science research findings that attempt to explain people's support or opposition towards gay rights.
From a very early age, all of us to learn how to relate to other people by placing them into social categories. For example, we put our parents and our siblings into the category of "family." Moms go into the category of "women" and fathers into the category of "men" (as you can probably tell from reading this blog, I am biased towards thinking that gender is the most fundamental social category we use to make sense of the world!). Cognitive scientists have studied extensively the processes that influence our categorizing behavior. However, only recently have psychologists begun to study how people think about categories themselves. The tendency to see categories as very fixed and stable is referred to as psychological essentialism. Psychologists have found that essentialist thinking can often lead to prejudice, as is this case with both gender and race. For example, the more that somebody thinks that women and men are essentially different from one another, the more likely they are to endorse traditional gender roles. They are also more likely to stereotype people based on their gender. The same is true for race: beliefs in biological differences between races have been found to increase stereotyping.
Homosexuality is a strong exception to the rule that essentialist thinking by itself automatically leads to more prejudice. 
Instead, researchers have found that different types of essentialist thinking underlie people's views about homosexuality. Social psychologists Nick Haslam and Sheri Levy found that people who think about the category "homosexual" as discrete, fundamental, and informative are more likely to hold prejudiced views against gays. Specifically, this type of thinking includes seeing the category of homosexual as clearly defined (e.g. you are either homosexual you are not), fundamental (e.g. all homosexuals are fundamentally like), and informative (e.g., it is possible to make important inferences about anyone who belongs under the category ‘homosexual'). In contrast, people with the essentialist beliefs that homosexuality is biologically-based, immutable (i.e. can't be changed), and is universally-occurring are actually more tolerant and accepting towards gay people.
Therefore, the study of psychological essentialism - and more broadly, how people make sense of social categories - can help us understand the roots of seemingly prejudiced behavior. People who believe that homosexuality is a choice rather than biologically determined may not see themselves as discriminatory by wanting to eliminate same-sex marriage. On the flip side, if you believe that homosexuality is rooted in biology and cannot be chosen, measures such as Proposition 8 seem incredibly unfair. Therefore, arguments between people holding different essentialist beliefs about a social category are unlikely to lead to fruitful discussion. In a way, debates about same-sex marriage run far deeper than political disagreement-they may actually point towards important differences in the way that people make sense of their social worlds.
