Sure! First, let's take a look at the importance of the work as a whole. The essay you mention, by James A. Snead, is found within a book called Racist Traces and Other Writings. There are some really interesting things about this collection. First, it was published after Snead's death. Second, it contains no less than nine essays followed by five short stories, all by Snead.
The essay called "European Pedigrees" is the eighth of the nine essays. In "European Pedigrees" as well as the other essays, Snead focuses on European and African connections, especially in regard to culture.
In "European Pedigrees" Snead presents a new concept that he calls "contagion," which is the tendency for people with any African descent to claim the huge variety of African cultures as one identity. Snead's point is that this erroneous "compression" into one identity makes any critic into a racist or, at the very least, a nationalist. Therefore, Snead condemns these "contagions" as "flattened perspectives." There is also something very important to note about the existence of such contagions:
Perhaps the most important aspect of cultural contagion is that by the time one is aware of it, it has already happened.
Far from being "flat," any kind of modern thought on this subject has to submit to the overlapping ideas of a growing world, knowledgeable about the different cultures within it and within the continent of Africa. Any "contagion" that turns one of these different cultures into only "African" polarizes the identity as against all others. Boundaries, then, can never be traversed unless countries and continents can understand their interdependence.