Often, one hears idioms like "the human race" or claims like "human races are merely a social construct". Such expressions are not scientific. The biological truth regarding humans is as follows:
Humans are the genus Homo, which resorts under the family of Hominidae, which belongs to the order of Primates. A genus is sometimes subdivided into species; in the case of Homo, a number of known species are Homo habilis, Homo erectus, Homo ergaster, Homo heidelbergensis, Homo neanderthalensis, and Homo sapiens. These are all humans, and most of them are extinct. Although species are breeding populations, related species can sometimes interbreed, and their offspring is sometimes fertile, hence the proportions of Neanderthal and Denisovan D.N.A. in current Homo sapiens, which would otherwise be impossible.
Notice that humans are not a race, not even a species, but a genus comprising a number of different species, which in turn may each comprise many races.
Species may be subdivided into subspecies, also called races. A subspecies is a population living in relative reproductive isolation from the other subspecies that make up its species, and having developed visible and behavioural characteristics that enable it to be distinguished from those other subspecies. By any biological definition or understanding, Homo sapiens has a number of subspecies that can be readily distinguished, such as Negroids, Caucasoids, Mongoloids, Australian Aboriginals, Native Americans, and some more. Despite the current possibilities of intercontinental travel and contact, the largest subspecies retain a strong tendency to procreate within-race, with only a marginal amount of mixing, the result of which is mostly not bred back into the large top-level subspecies, hence the formation of new mixed-race groups and the gradual disappearance of some of the smaller, older racial groups. A large and more or less homogeneous mixed-race group may come to be seen as a newly formed subspecies. Such groups tend to form in the subtropical regions. It is possible that, in the course of human evolution, new species have sometimes evolved from such successful mixed-race groups.
The claim, sometimes expressed, that humans are now blending together into one global race, is unfounded, and also not consistent with what one tends to see with competing subspecial populations of non-human animals. Races do not generally blend together into one homogeneous population; what happens is rather that the least reproductively successful group disappears in favour of the other, or, sometimes, that they develop into separate species. Both of these options are plausible in the case of humans. In fact, if no political sensitivities existed and humans were considered with the same degree of objectivity as are non-human organisms, it would not be obvious to classify all currently living forms of Homo under the same species.