If race refers to physiological qualities, what do sociologists mean when they say that race is socially constructed?

The reason why sociologists say that race is a social construction is because what it means to be "white", "black", "Latino", "Asian", etc., is defined according to culture, time and the place. The meanings of these categories are changed over time. However, what does not change is that the racial groups are placed in a hierarchy, with white people or with lighter skin in the upper part; people of non-indigenous color subjected to people with lighter skin; Black and indigenous people in the lower part of the racial system. race is an externally imposed social category. Unlike ethnicity, which describes both aspects of ancestry as well as culture and personal identification, race is ascribed by society.