Brown eyes are predominant in humans and, in many populations, it is (with few exceptions) the only iris color present. It is less common in countries around the Baltic Sea and in Scandinavia.
In humans, brown eyes contain large amounts of melanin within the iris stroma, which serves to absorb light, particularly at the shorter wavelengths. Brown eyes are the most common eye color, with over half of the world population having them. They are also the most dominant eye color gene. Very dark brown irises may appear at a glance to be black.