Schemas, social categorization, and such...
When looking at different sports, it seems like there is an obvious majority of one group over others. For instance, blacks dominate the populous of basketball and somewhat in football. There is a majority of whites in racing, golf, tennis, baseball, hockey, croquet, et cetera. When looking at different professions, there is a majority of whites in managerial or executive positions. The lack of a certain demographic would have to do more with social influences. For instance, it is fact that an average white male is more likely to come from a higher socio-economic status than an average minority. With this comes a different life-style (i.e. wealth, education, family structure, leisure activities).
Certain sports require money to get started, such as racing, golf and hockey. Obviously a person without money will be less likely to have the opportunity to take part in these sports. Certain professions require specific training and education. Generically, people are more likely to succeed at things they are able to do. Opportunities arise from exposure. Different demographics are going to have different tendencies. Another interesting aspect is the idea of self-fulfilling prophecy, demonstrated by the experiment known as "Pygmallion in the Classroom."
In the study, teachers were told of specific students that scored high on competency exams and such. They were also told of specific students who were problem students or scored poorly on equal exams. When compared at the end of the year, the "smart students" were found to do better than the "bad students." Keep in mind, the students were randomly assigned as being "smart" or "bad." The teacher thought that the smart students were really smart, even though this was not necessarily true and vice versa about the bad students. The success or failure of the students had more to do with the teachers attitude and resulting behaviors towards each student. Obviously, the teacher had a favored bias towards the "smart" students. Consequently, the teacher was likely to spend more time with those students, have more leniancy, et cetera. The point of the matter is, preconceived notions can affect the outcome and development of a person in certain situations.
Of course, there are always exceptions to the norms...
PS-Please don't debase my argument because it is "book talk." It is very relevant to this subject. And, I am sure many people on this board have experienced at least one of these ideas in their lifetime, therefore making them life experiences.