I believe race to be more of a concept created by society rather than true classifications based on important biological terms. "Races" are really just groups of people placed into different categories based on their physical characteristics such as skin color, hair texture, and facial features (such as nose, lip or eye size and shape) or region of birth. The concept of race seems to be an easy way of grouping people together for means of trying to emphasize unimportant differences or to make oppression and discrimination seem more justified (almost like a racial caste system).
Differences between races are cultural as opposed to biological; they are learned or adaptive differences and not scientifically proven differences in genes. Most of the noticeable physical variation among peoples of different races can be explained in ways other than biological variation. Natural selection plays a large role in the appearance of these dissimilarities.
The theory of natural selection states that those who are adapted in the necessary ways will be the ones who will survive and thrive, creating more similar offspring. Region of birth often dictates physical characteristics. People who live in regions of the world with more intense sunlight will most likely have more melanin present in their skin and have darker skin pigmentation. This will be because melanin is a naturally produced skin protectant, more of this substance results in darker skin. People living in this area with darker, better-protected skin will most likely be the ones able to survive and reproduce there (creating a "race"). The only difference between darker skinned and lighter skinned people is the amount of melanin in their skin. Is region of birth and melanin amounts important and obvious biological variation? I think not.