Excessive alcohol consumption kills about 88,000 people in the U.S. 2 In 2012, approximately 11.2 million adult men, 5.7 million adult women and 855,000 persons aged 12– 17 had AUD in the U.S. In 2013, alcohol dependency was formally reclassified together with alcohol abuse as “alcohol use disorder (AUD).”Įxcessive alcohol use is the third leading modifiable cause of death in the United States. So the parts of the world where descendants of that founder individual are most common have the highest frequency of blue eyes where those descendants are rare, darker eye colors are the dominant eye color.Ĭontinued use despite knowledge of alcohol-related physical or psychological harm. 1 The evidence suggests that all people with blue eyes carry this same variant. About 6,000–10,000 years ago, probably in the area of the Black Sea, a single individual was born with a mutation that programs reduced OCA2 gene expression and blue eyes. As our ancestors migrated out of Africa, some found their way into Europe. The current genetic evidence suggests that the first humans had brown eyes. However, as many as seven other genes can impact melanin deposition, resulting in shades of blue and green and explaining why two blue-eyed parents can have green-eyed children.Įye colors other than brown only occur in individuals of European descent. 1 The more OCA2 activity in the iris melanocytes, the darker the eye color. The OCA2 gene on human chromosome 15 has a major impact on eye color by producing a protein that controls melanin formation and processing. Most Americans are taught that eye color is a single-gene trait - that a brown-eye gene variant is dominant over the blue-eye variant. Right: melanosomes (colored ovals) increase in number and melanin content in (top) blue eye melanocytes, (middle) hazel eye melanocytes and (bottom) brown melanocytes. Left : representations of the pupil (black) and surrounding iris color in (top) blue eyes, (middle) hazel eyes and (bottom) brown eyes. Eye color is determined by the number and melanin content of melanosomes within the melanocytes of the anterior iris stroma.