Is social class or gender more important in shaping the life of an individual born in the United States today?
Social class, because it is so closely tied to economic class. Economic class determines where we live, how healthy we are, how educated we are, and how safe. These are key and salient details that determine the course of our lives and the shape of our daily lives, and economic/social class is no respecter of gender. Poor white men face the same issues as poor white women when they find themselves in the lower social and economic classes.
To draw an analogy, there is a greater difference between classes than there is between genders just as there is a greater difference between people from rural areas and those from urban areas than there is between people from the North or the South. As a previous poster has remarked, the inner workings of males and females of the same class is very similar, just as the experiences of rural people are more closely aligned to other rural people's, even if the people are from another entirely different region of the country than they are to urban people of their own geographic area.
For, in each case, there is an attitude about many facets of life as well as a value system that one acquires from those around whom one grows. Thus, the rural Kentuckian can understand another rural person from Vermont better than he can a person from an urban area in Kentucky. Likewise, the class in which a person lives affects his or her ethics and attitudes, dividing him or her from other classes that often often differing values.
Hopefully gender is less important in today's world. This is not to say that there is still quite a way to go in terms of achieving quality, but that I personally think that there have been more advances made in terms of gender equality than class equality, which is why I think the social class you are born into has the most impact on a person's life.
In my opinion, social class is more important in shaping the lives of Americans than gender is. I say that because I believe that men and women of a similar social class tend to have more in common with one another than they do with people of the same gender from a different class.
For example, you can argue that well-educated Americans share a set of values, whether they are men or women. They tend to believe in the equality of the sexes, for example, and in social tolerance of sexual or religious minorities. By contrast, there is a large difference between attitudes on these issues between highly educated men and men with only a high school education.
This is not to argue that gender does not matter. I am simply saying that I think class matters more.