The Scientific Revolution's enthusiasm to classify and ""order"" nature led to a new practice of grouping people by what?

Race.

Explanation:

Scientific Revolution is acknowledged as the chain of events that led to the evolution of modern science which metamorphosed the human views or thoughts on nature and its components.

As per the question, the Scientific Revolution passion to categorize and 'order' the nature as they believed in the proposition that every phenomenon or process existing on the Earth could be elucidated mechanically through the natural laws and standard principles led to the emergence of a new practice of categorizing/grouping people through 'race'. The humans being were demarcated into 'unequal and distinct groups' based on their race that eventually gave birth to the brutal practice of slavery in the U. S. and various other European countries. Thus, 'race' is the answer.