Bongwadi Bja Go Rothotha Bobodu

Man has spend decades after decades studying the constitution of the human body from the early times of Andreas Vesalius to the modern times where robotic arms form part of the human functionality and extend its use.
But with all the knowledge in the world man has not figured out yet why he has nipples.
What is the function of nipples on a male human body?

It cannot be for esthetic reasons because some males have nipples that are barely visible and it not like people walk around showing their nipples off.

History, fiction, etc, they rarely touch the subject of nipples in males which leaves it to be the greatest mystery of all time! Wait... maybe not greatest but still a mystery nontheless.