The application of evolutionary principles to the study of human variation: a. replace earlier views based solely on observed phenotypes. b. allowed scientists to divide the human species precisely into well-defined races. c. reinforced traditional views of races as fixed biological entities that do not change. d. has been of little value for understanding human variation. e. allowed scientists to ignore the adaptive significance of most traits.

Helped replace earlier views based solely on observed phenotypes.

Explanation:  Historically, physical differences such as skin color were used as the basis of racial classification due to differences in skin pigment being so noticeable.

This thinking can be traced back to before World War II, where most studies of human variation were solely based on the visual phenotypic variations. It was only in the second half of the twentieth century that we started looking at genetics and realized that we could not trace human evolution based on visual phenotypes observed,  but rather genetic heritages.