just my opinion:
even among animals they are no true race:
what is relevant is the specie: the faculty to reproduce with the help of an opposite sex mate -
what we find is raciation, a natural phenomenon based on genetic mutations and the selection of these mutations under certain conditions: this selection can have a higher or lower degree according to environmental pressure, isolation or at the contrary contacts maintained (and the population size) producing more or less differentiated groups (between them) AND more or less homogenous (within them) -
so human beings "suffered" the same conditions as the animals at first stages (raciation) but our present human stock seams being extracted for the most from a small enough population '"race" then? why not?) that evolved at different times on the way to raciation too, but keep having some contacts between its differents subsets, that led to less differentiated "branches" compared to the animals world. saying there are or there are not different races among mankind is a unanswerable question I believe...
I should say human beings are grouped or WAS grouped in "imparfect races" (different from the notion of "specy") - even plants could by classed as "races" or not "races"...
concerning mankind, we can see some great enough processes of differentiation leading to some concept of 'caucasoid', 'negroid' or 'mongoloid' types, even if the frontiers are very less clear than among animals "races"...
the objection that some "white" man could be closer to a "black" or "yellow" man that to another "white man" concerning some gene (HLA: blood, body tissu) is not a very available one: we share a lot of genes with other species from the pig to the fly, why not some fishes, but e are not pigs nor flies... some autosomals mutations on some loci can be very old and lead to a heterogneous population concerning these loci even if ONE and UNIQUE "race" for other aspects -
let's say locus A >> mutation >> A1, A2
a small subset of population go away with these alleles A1, A2
with time other mutations occur on B,C,D,E [...]X, Y, Z alleles with selection giving way to a new "race" (group) concerning these last alleles, but the heterogeneity of A could remain even if the percentages could vary - the members of the different subsets of the previous population can evolve very far one from another concerning other genes and keep nevertheless the A1 and A2 variants - if the A gene is not submitted to strong selection, it can keep is variants in a sufficient size population: but as a whole we see that with time, the human groups tend to homogenize themselves slowly, loosing some of the old genes they shared between them, at different speeds - but some heterozygotic conditions for some genes can (it seams almost proved) provide some advantage for health and help ot conserve variance (diversity?) -
all the way, human groups seam having crossed one together often enough when it was possible, exchanging genes that from a ONE group statute got a SEVERAL groups statute, more when they was positive under pressure, either in an homozygotic or in an heterozygotic position -
saying that there are several species among human beings is stupid - saying it is not possible to see more or less distance between big human groups and even between some subgroups is as stupid, but sure there is no barreer at all -
in short: we surely undewent strong processes of raciation but after that we took the way of DEraciation -