The five senses are specifically superior to those of animals in point of constitution and efficiency so as to endow him special merit thereby.
The eyes are set in the head as if a lamp set on a lamp post to enable him to see everything. They are not set in the lower parts of the feet to safeguard against injuries or accidents during work or movement, which would have ailed them and impaired their efficiency. Had they been set in the middle part of the body like the belly, the back or the breast etc., it would have been difficult to resolve them or to see things by sudden turning. The head is the cynosure the best place for these senses in suitability compared with any other organ.
The senses are five in number to respond to all kinds of stimuli and to leave no stimulus undetected.
The eyes are so constituted as to distinguish between colors. The colors would have been meaningless without such ocular proficiency, since these colors exist as a means whereby things maybe distinguished from one another, or the eyes may get recreation from them.
The ears are set in the head to detect sounds, which would have been meaningless without such auricular proficiency. Similar is the case with other senses – without proficiency of the sense of taste, all tasteful foods would have been dull; without the sense of touch the sensation of heat, cold, softness, hardness, would just as well have been non-existent; and without the sense of smell, all scents would have been inert.
Reference: Tradition of Mufaddal, Pearls of Wisdom from Imam Ja'far al- Sadiq ('a).