Cultural anthropologists, says Professor Edward Fischer of Vanderbilt University, like to think in terms of a peoples' mental models - ideas widely shared within a population that actually make up much of that population's culture. In the United States, for instance, people tend to share such ideas as "time is money," and the (obviously mythic for most) "American dream." Then there are such erroneous models as the idea held by many that weather causes colds. These "cognitive models" can change - not too long ago alcohol or drug addiction was a moral failing, hard-to-deal-with kids were naughty, and soldiers affected by shell shock were just weak. Now the culture has agreed that addiction is a disease, bratty kids can have attention deficit syndrome, and soldiers can suffer from Post Traumatic Stress Disorder.
But different cultures' cognitive models can vary widely: From the danger of the "evil eye" to whether menstruating women (or just women) can "pollute" males to what constitutes incest, cultures around the world have their own definitions of what constitutes "common sense." (For instance, some matrilineal cultures think marrying your mother's brother's daughter is incest, while marrying your father's sister's daughter is ideal.)
Mental cultural models are the sort of thing you don't think about. For instance, it is a common and uncontested American view that a mother and a newborn baby instantly bond. The idea is so pervasive that new mothers who don't feel that bond are shattered and become depressed. Yet studies show that in poverty-stricken regions of the world, where half of a woman's babies survive less than a year, mothers don't shed a tear when a baby dies. They invest no love in a baby until he or she begins to thrive. This shows, says anthropologist Nancy Scheper-Hughes, that instant mother-child bonding is nothing but a Western ideology we have wrongly assumed is universal.
Even such basic ideas as the two sexes - talk about common sense! - can vary with cultures. Take the Berdasche of the Northern Plains Indians, or the fa'fa'fine of Samoa - men who early on adopt women's dress and women's work. Samoans who choose that path really get pissed when they vacation in Australia and get accused of being gay or transvestites. Australians (and Americans) have no category for them. Samoans, meanwhile, value a person who can do both women's and men's work.
Anthropologists pride themselves on doing wide-open, subjective science. We could argue. But I think they are right when they suggest that while studying other cultures, we can learn something about ourselves.