Earlier quoted context omitted.
A group of people that have lived long enough in relative isolation that they became unique, distinguished and separate from other races.
"long enough"? " relative isolation"? "unique" how: genetically? culturally? phenotypically?
Shortly:
- Unique how? Optimally genetically, but this has practical problems that the field of paleogenetics is trying to work on. Until then must use: classical morphological features, odontology, dermatoglyphics, biochemical characteristics.
- How long enough? Depends on the type of group. There are different levels of human group classification, both above the traditionally understood "races" and a lot below that.