When people come in to contact with one another they tend notice differences they see in one another. These differences can be attributed to the genotype and phenotype variation between people. It tends to not be biologically significant to divide humans in to racial groups it is more of a social concept. The various characteristics such as skin color, shape of face, hair and eye color, nose shape and hair form are used in categorizing people in to specific races. Race is a powerful social concept that affects many aspects of our culture now and in our history.
In the past you would see much more endogamy due to breeding isolates. But now with more social acceptance and modern transportation we are seeing much more exogamy. This in turn has widened the gene pool and allowed much more genetic variation. With these changes come less of a chance and or preference for inbreeding like we have seen in our history. Inbreeding tends to increase the chances for the offspring to have genetic disorders there for is harmful to the population.
The problem with this social categorization system it tends to lead to certain races believing their traits are more favorable. Once it is believed that one race is better than other that type of thinking leads some to believe in