Daily Archives: April 5, 2014

Blue-eyed Humans have a Common Ancestor

A team at the University of Copenhagen were able to track down a genetic mutation that took place 6 to 10,000 years ago in the OCA2 gene that was able to create a “switch” which turned off the ability to produce brown eyes, by limiting the action of the gene to produce melanin in the iris, and dilute brown eyes to blue. Further, there is limited genetic and phenotypic variation in the eyes of blue – eyed people. For example, variation in melanin causes the differences in brown and green eye color, but blue-eyed individuals exhibit very little variation in the amount of melanin in their eyes, and also have inherited the same mutation at the exact same locus on their DNA, lending to the theory that all blue-eyed individuals have a common ancestor and the mutation is found to be passed maternally. Mitochondrial DNA was examined from diverse countries such as Jordan, Denmark, and Turkey (1).

However, the question most people, at least when it comes to our class, have is what does this mean in the context of evolution and natural selection? The answer: depends on who you ask. Some articles (1) claim that the mutation of brown eyes is neither a positive or negative mutation. Just as other mutations (hair color, baldness, etc.) do not increase or decrease a human’s chance of survival; hence nature has attempted to merely switch up the genome in this cocktail theory. It is interesting from a student perspective, to remind ourselves that sometimes nature does not necessarily directly work in favor of increased fitness.

On the other hand, others assert (2) that the mutation arose through the mechanism of sex selection, which we in our previous class understood as “ornamental demonstration” where in an area of increased competition for reproduction, males and females will choose their mates due to one peculiarity or phenotypic variance (such as with seen in the demonstration of male peacocks) in an effort to diversify genes and subsequently increase fitness.

Though, I agree much additional research is needed regarding the mechanism and the common – ancestor theory itself, it is an interesting topic, and increased studies across multiple population – types may be helpful.