In North American culture people tend to believe in the term race and try to categorize it terms of skin color. The usual system is : White, Yellow, Red, and Black. It is also used in a hierarchy, yes the established social system in North America is indeed racist in social terms. How dare I call our culture racist?
Well lets see lets put you to the test, shall we? A white mother and black father have a child, what race is the child? Now that I called you a racist you'll be inclined to say "mixed", but the cultural reality of the matter is that the child would get the race of the lower ranking parent.
For instance in the case of Obama's parents: White + Black = Black
Tiger wood's parents: Black + Yellow = Black
This is the state of our cultural frame work, and how the mechanics of it are recognized and established. These are so deeply rooted into our history that they will not change for a long time. It is a purely social construct, and the hierarchy it is based upon is a mythology carried forward by racist ideas.
Even more interesting that the intersubjectivity of the idea of race changes from culture to culture. Many other countries and regions of the world have their own historical social constructs which race is depicted differently. Some include more than 300 races in total.
However back to the idea of hierarchy of race in North America. It was first established from the beliefs in Europe that Whites were the superior entity and much more "pure", "intelligent", and in some cases some peopled we were "God's last and best creation", these ideas were socially acceptable for the time because this is when major colonization was being undertaken across the world. When it cam to North America, these ideas were used to justify the killing of Natives(Reds), and slavery of Africans(Blacks).
This is a more familiar history to some, and a past which is often not discussed or brought up because of the implications of such wrong doing in today's culture. It makes many uncomfortable, but the reality of the matter is that these social constructs haven't changed much. The social hierarchy which is invisibly put in place but our cultural frame works are quite racist. Only acknowledging the biases before us will allow our culture to shift into a better ideas about race.
Science doesn't deal with race, because it is an intersubjective social idea rather than a scientific one. Science in stead views us as a single species with many variations, which is the reality of it. Genetically there is far more in common between these "races" than their is different, and the differences are merely a result of thousands of years of gene separation and environmental changes.
We are Homo sapiens. Nothing more.