It's not 'socially constructed', some groups of people from different parts of the world (ie: races) have generally different physical characteristics due to the different environment and this is visually evident.
For instance, a black has black skin because it better suited to the type of hot sun of the African climate etc.
and another difference that exists between races is than asians have longer torsos and shorter limbs than whites and blacks of the same height
take a 6 foot asain man and a 6 foot black man and the asian man will heve a long torso and shorter legs than the black man of the same height as he
and another difference has to do with the storage of bodyfat, blacks store more fat in their limbs than do whites, and whites store more fat in than torsos than do blacks