Final answer:
Race cannot be scientifically defined by a set number of traits due to the complex genetic diversity and polygenic nature of human characteristics. Researchers agree that the concept of race is not a valid biological categorization but a social construct that does not capture the subtleties of human genetic variation.
Step-by-step explanation:
There is no set number of traits to define a human population into races because human traits vary greatly and do not conform to fixed categories. For instance, skin colour is a spectrum ranging from very light to very dark, rather than a few distinct colours. Genetic research has shown more variation within these arbitrary racial groups than between them. Moreover, traits like skin colour are influenced by polygenic inheritance, meaning they are controlled by multiple genes, which makes it difficult to categorize people into discrete racial groups based on a few characteristics. Due to this complex variation, biological anthropologists, geneticists, and statisticians agree that race is not a valid scientific classification, but rather a social construct that fails to accurately reflect the immense genetic diversity within the human species.