The eyes have it

Indeed, we all have 99.9% of exactly the same DNA – which is what makes us human. The other 0.1% is what makes us unique. This may sound very little but it does, in fact, represent 3’000’000 differences on the molecular level!

Blue is unique

Among these 3’000’000 differences, there is one which makes our eyes blue. The fact was discovered in 2008 while scientists were carrying out research on a large Danish family; the father’s eyes were brown, the mother’s blue, and they had 17 children and 20 grand-children. A simple change of one nucleotide in the HERC2 gene was enough to explain the blue colour that ran in the family. Even more surprising: this same difference is shared by the great majority of individuals with blue eyes of European origin.

Find the difference

Bioinformatics can compare the sequence of the HERC2 gene between many individuals. Swapping this particular adenine (A) for guanine (G) is what makes eyes blue.

Blue in the past

This astonishing change of eye colour seems to have appeared in Europe during the neolithic period, 6’000 to 10’000 years ago, when many farmers left the Black Sea to migrate to Northern Europe. Blue eyes have therefore survived time and crossed the millennia. For what reason? Any change in our DNA which is preserved must be beneficial to our species; but why keep our eyes blue? No one has found an answer yet…