Species: Biology. the major subdivision of a genus or subgenus, regarded as the basic category of biological classification, composed of related individuals that resemble one another, are able to breed among themselves, but are not able to breed with members of another species.
Race: 1. An interbreeding, usually geographically isolated population of organisms differing from other populations of the same species in the frequency of hereditary traits. A race that has been given formal taxonomic recognition is known as a subspecies.
2. A breed or strain, as of domestic animals.
Now if we say Human Race, that means that there must be another "race" that we can breed with, in a different geographic location.
However, if we talk about the Human Species, made up of various races, it makes much more sense. Humans cannot breed with any other organism (such as a monkey or any other humanoid).
Now the races that make up the Human Species are classified by geography, and heredetary traits. Skin color, type of hair, eye color, etc are all heredetary traits. IE. Two black people cannot have a white child (except in the case of an albino, but even so, that albino is still "black".). Before massive migration, most of these traits were isolated in their own geographic area.
Blacks in Africa, Asians in Asia, Whites in Europe, and "Browns" in America.