According to wikipedia:
Since there are easily defined groups of humans which share a particular phenotype, I don't see how any of those three could apply. There are clear dividing lines among separate groups. These groups do not fade imperceptibly into one another. There is gene flow between groups, but it is not substantial. The variation within the species is not random, nor is it individual, nor is it unrelated to genetic transmission.A monotypic species has no distinct population or races, or rather one race comprising the whole species. Monotypic species can occur in several ways:[citation needed]
- All members of the species are very similar and cannot be sensibly divided into biologically significant subcategories.
- The individuals vary considerably but the variation is essentially random and largely meaningless so far as genetic transmission of these variations is concerned.
- The variation among individuals is noticeable and follows a pattern, but there are no clear dividing lines among separate groups: they fade imperceptibly into one another. Such clinal variation always indicates substantial gene flow among the apparently separate groups that make up the population(s). Populations that have a steady, substantial gene flow among them are likely to represent a monotypic species even when a fair degree of genetic variation is obvious.
On the other hand, a polytypic species, which we are, is defined by wikipedia as:
Interracial breeding is something of a new thing in the human species so, while possible, until recently (and even now it is comparatively rare) subspecies (or 'races') did not generally interbreed, but certainly could if given the chance. As we determine the taxonomy of other species based largely on differences in phenotype, so we can with humans. Phenotype being an expression of genotype, or heritable traits and morphology if you prefer, it makes sense to classify humans into subspecies. Especially so as modern medicine has made numerous discoveries regarding the susceptibility and proper treatment to and of diseases linked to particular subspecies.A polytypic species has two or more subspecies, races or more generally speaking, populations that need a separate description.[4] These are separate groups that are clearly distinct from one another and do not generally interbreed (although there may be a relatively narrow hybridization zone), but which would interbreed freely if given the chance to do so. Note that groups which would not interbreed freely, even if brought together such that they had the opportunity to do so, are not subspecies: they are separate species
There really is no argument to be had on a scientific basis. The 'no subspecies' 'no races' (the terms are interchangeable, or would be if it weren't for PC trash) debate is purely social. We all want to be equal. We want the old racial biases and stereotypes to just go away so we can live in peace and harmony and all that. Very nice, but it has nothing to do with science.