Despite extensive efforts, no one has ever devised a satisfactory scientific system of race classification.
nor can they because:
A race classification system is discrete (you're either this or that), but race traits are continuous.
Next: The independence of racial traits
It is worthwhile noting that in the United States extraordinary efforts were made to devise systems of racial classification and to prove white superiority. One critical source of American scientific racism was the work of Samuel G. Morton (1799-1851). Morton rejected the biblical origin story and argued that different races had different creations (a theory called polygenesis) and thus, human beings were members of several different species. He backed his work with measurements of the skull sizes of different people and claimed to find that Black people had smaller skulls than white people and were therefore less intelligent. His claim that Black and white people had different brain sizes was widely accepted as scientifically valid until the middle of the 20th century. It has since been disproved and today is considered nonsense. Numerous scholars followed Morton. The anthropology we've been focused on follows Boas and his descendants and these were strongly anti-racist. However, anthropology, particularly "physical anthropology" had more than its share of racists. In the 20th century, the most famous of these were the anthropologists Earnest Hooton (1887-1954) and his student Carleton Coon (1904-1981), both of whom taught at Harvard (Coon moved to the University of Pennsylvania in 1948). Hooton and Coon attempted and failed to produce scientifically acceptable racial classification systems. "Physical anthropology" is now usually called Biological Anthropology and is firmly anti-racist. In fact, one reason for the name change is probably to put some distance between current day biological anthropologists and people like Hooton and Coon.