In humans, brown eyes result from a relatively high concentration of melanin in the stroma of the iris, which causes light of both shorter and longer wavelengths to be absorbed.
Dark pigment of brown eyes is most common in East Asia, Southeast Asia, South Asia, West Asia, Oceania, Africa, Americas, etc. as well as parts of Eastern Europe and Southern Europe. The majority of people in the world overall have dark brown eyes.
Light or medium-pigmented brown eyes are common in South Europe and parts of Asia (Afghanistan, India, Middle East, and Pakistan). Light-pigmented brown eyes are sometimes referred to as "honey eyes".