What constitutes a “race”, a “species”, a “breed” and other such abstract divisions of living organisms? I.e what are the definitions for these various terms?
For one thing, I understand there is no such thing as races in the human speices, other than “the human race”. The argument I’ve read is that there is so little genetical variation between various ethnic groups that the variation within a group can be greater. Does this mean that the only scientifically valid term is “ethnic groups” - and that this term is more of a cultural label than biological?
The term “Species” is generally used to denote that group of animals that can breed with one another and produce fertile or virile offspring.
However, that definition isn’t universally relevant (for instance, at the microbiological level) or used (populations that are separated from mating - for instance, two populations of ants that are morphologically different and live on different continents that might actually be able to mate, but never do.) It’s also a relatively recent usage of the word “Species” - in Darwin’s time, “species” was a largely subjective call based on observed differences.
As you allude yo, “Breed” and “Race” are wholly subjective.
Currently, the most generally used definition of species is that of the Biological Species concept. Simply put, species are those populations which do not regularly produce fertile hybrids in nature. (This definition can be difficult to apply if two populations do not come into contact in nature; in this case decisions are basically rather arbitrary.) There are other species definitions besides the BSC; the more recent Phylogenetic Species Concept is popular in some circles.
“Race” as used by biologists is basically equivalent to “subspecies.” There is no clear definition of subspecies, and many biologists regard them with disfavor these days (the PSC would eliminate them entirely). In general, they are recognizable regional variations within a species. Some originated when various populations were separated in the past, but now have come together again and hybridize extensively in areas of contact.
In some cases, morphological features vary in a gradual fashion across a species’ range. This is known as clinal variation. In the past, subspecies were often defined on such clinal characters, but this is now disfavored. Since human “racial” differences are mainly clinal in nature, they would not be recognized as having validity as subspecies under modern taxonomic concepts.
“Breed” refers to a variant of a domestic species established through artificial selection.