Cultural Supremacy has been proven to exist in many countries. For example, in US and Oceania, Asians tend to perform better on tests than their white counterparts. In places like Mexico, white men tend to be wealthier tend ethnic Mexicans. Also, very few people still follow Greek Mythology. Period. -
All cultures have the ability to create their own customs, rituals, belief systems, etc. These cultures are all equally important and supreme within their own bounds. It is irrelevant how many people prefer one culture over another simply because cultures were entirely created by groups of people, and people have the same amount of intrinsic value derived from their existence as human beings. Therefore, all cultures are also equal, because they are just a direct culmination of the experiences and beliefs of those individuals.
@General-Z: Yes, these differences do exist, but they do not exist because one culture is superior to another, but because of the mere exposure effect (and peer pressure). For example, standardized tests were designed within the confines of a particular culture (regardless of what those testing communities may claim) and there will be an inherent bias toward people of a particular culture, since the tests have that particular culture's bias (i.E. The SAT emphasizes rationalism, mathematics, and English skills. These skills are especially derived from what the American and European cultures deemed important since the Scientific and Industrial Revolutions). This culture-bias is what determines who does well on those types of tests, not any inherent supremacy.
It is a similar case with wealth and power. The way societies determine prestige and wealth is also directly tied back to what most European countries and America determine is the correct way to distribute wealth/power (those who work the hardest, fight to the top, etc.).
With religion it is a bit different, but still is directly influenced by the same cause as before (mere exposure and peer pressure). Greek Mythology, for example, was subscribed to by the ancient Greek culture. Then the Roman culture, with superior military power, came along and altered Greek Mythology. Later the Romans picked up Christianity because of pressure from Christians to support it. Then the European "barbarians" came and ravaged the Roman Empire, imposing their culture on the Romans.
In conclusion, this concept of "cultural supremacy" has arisen (as it always has) from certain cultures who are the current military powers. Their sphere of culture-influence and militaristic-influence are very closely tied together and are comparatively extremely large, so they believe that their culture is somehow inherently supreme. In reality, people subscribe to their culture because of mere exposure effect (from the nation's military might spreading that nation's agenda across the known world) and from peer pressure (due to the nation imposing certain things, be it explicitly or implicitly, on every other culture they meet in order to conform other cultures to the nation's culture standard). It happened with Rome. It happened with France. It happened with Britain. It's currently happening with the United States.
Yet most people don't look at the trends on a macro scale and figure out what is actually going on, so they just assume that whatever culture is being pushed is automatically the best.