To answer some of the questions asked:
1. A few subspecies of Homo sapiens have been recognized-of which only one, Homo sapiens sapiens, seems to be left. Others, like Homo sapiens idaltu or balangodensis seemed to have gone extinct.
Additionally, one should not forget certain so-called "archaic" Homo sapiens whose precise phylogenetic status is often debated.
2. What makes a species a species and a subspecies a subspecies? Ernst Mayr's original concept of a species = "groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups" becomes more and more questionable, not just because of various examples of fertile interspecific hybrids. A very basic overview:
[ame=http://en.wikipedia.org/wiki/Species]Species - Wikipedia, the free encyclopedia[/ame]
Nowadays, gene sequence comparison is favoured to decide whether the differences are sufficient to categorize a new species or not. However, it is often questionable whether this is the wisest and ultimate of all solutions.
3. There exist differences in the morphology and genetics of, say, an Ainu, a San or a Basque. These differences can be more or less subtle; some "racial" features, like epicanthic folds, body size or the complexion of the skin are more obvious for the untrained eye than others. However, nowdays "race" classification systems for modern humans are no longer considered valid from a biological point of view, but still used in a social context/police profiling/forensic anthropology...
