Race Without Color (Diamond)

In this article, the author says that anything can be a criterion of race
through trying to categorize humans by 4 biological factors.
Also, he advocates that animal traits are for 3 reasons
(natural selection, sexual selection, and no function).
His main opinion is that humans should not use racial classifications because it is arbitrary.
The content of the article is interesting and the example of 4 factors are persuasive, but lack of referenced sources and citations makes his opinion look subjective.

He introduced the example of warblers to explain the division of species and subspecies (race), and he says it is impossible to classify humans like them because of social context and emotions.
I believe that if scientists study humans purely for solving biological mysteries and the data will never affect social theories, humans can somewhat be grouped by one criterion.
However, it never be possible, so people should not use the concept of classifying humans into some groups.

If I have to define the word "race", I would say that race is one of cultural concepts or stereotyping  to group people caused by the difference of appearances.