“O, beware, my lord of jealousy,” Shakespeare’s Iago warns Othello, “it is the green-eyed monster, which doth mock the meat it feeds on.” This is not the only occasion in Shakespeare’s plays that jealousy is described as green-eyed – Portia in the Merchant of Venice does it too. But why green; dear Shakespeare?!
In Renaissance England it was not unusual to pair colours with emotions or personal qualities. This particular association – green eyes and jealousy – might however have originated in the Greek tale of Cupid and Psyche. In the myth, Cupid’s mother Aphrodite, jealous of the beauty of a mortal girl called Psyche, instructs her son to make Psyche fall in love with an ugly man. Cupid dallies, for he is in love with her himself, until he one day he misfires one of his arrows at Hercules who falls in love with Psyche. Psyche rather fancies him too (quite naturally perhaps!) and Cupid, overcome by jealousy, turns into a monster with green eyes and flies off with her.
In fact, there is no shortage of myths and stories in which green eyes carry a specific meaning. In ancient Egypt, green was considered the colour of good health, life and re-birth, and the Eye of Horus amulet – worn to protect one against illness – was most often made of green stone. In folktales around the world, witches, nymphs and water spirits often have green eyes: in English folklore we have Peg Powler and Jenny Greenteeth, in Russian and Slavic mythologies Rusalka, and in Japanese, Kappa – all spirits who inhabit shores and river trees – who were probably invented to warn children off dangerous waters.
But why did green eyes become considered as specifically mystical? One probable explanation is that they are so rare: less than two percent of the world’s population are estimated to have green eyes. They are most common among people from northern countries (particularly Iceland and Finland) and those with Celtic ancestry, and while green eyes can now occur in any part of the world as a result of migration over time, they are still extremely unusual on a global scale.
In migration across whole continents, big trade routes played a key role. In Northwest China, situated along the famous Silk Road, there is a village called Liqian in which two-thirds of the inhabitants have green or blue eyes and blonde hair. DNA tests conducted in 2005 showed that these residents had definite Caucasian ancestry – possibly Romans or Iranians who would use the Silk Road actively. Some have suggested the Liqians to be descendants of the legendary missing army of a Roman general Marcus Crassus, who disappeared in 36BC. However, since Liqian is situated along such a big trade route, the explanation might simply lie in the amount of people passing through it.
Another curious aspect of green eyes is that they really only appear to be green – that is, there is no actual green pigmentation in the eye. The human eye colour is determined by the concentration and distribution of melanin (pigmentation): the more eumelanin you have on the top layer of your iris, the darker your eyes appear. Green eyes tend to have low amounts of eumelanin, similarly to blue and grey eyes, but they also contain a much rarer yellowish pigment called pheomelanin. The appearance of green eyes is actually a sort of mirage caused by Rayleigh scattering (the dispersion of light off air molecules), the same phenomenon that makes the sky seem blue. Hence why your eye colour can seem slightly different depending on the light around you, or the colours you are wearing.
For a long time, eye colour was believed to be determined by certain dominating genes one receives from one’s parents. In 2007 however, a team of scientists from Queensland, Australia published a study in the American Journal of Human Genetics showing that up to sixteen genes contribute to eye colour. In practice, this means that a baby can inherit virtually any eye colour, regardless of the colour of its parents’ eyes. Things like radiation, disease, chemicals or medication can also affect and permanently change the pigmentation of the iris.
Coincidentally, The American Journal of Biological Psychology also in 2007 published a study in which there was a suggested connection between development of the iris and development of the personality. Researchers from Orebro University in Sweden discovered that the genes responsible for the development of the iris also play a role in shaping the frontal lobe – the very part of the brain that influences our personality. Using a person-oriented analysis, the team discovered that subjects with different iris configurations tend to develop along different personality trajectories. Not that a certain eye colour simply denotes a particular personality trait – having a pair of those rare green eyes does not automatically make you prone to jealousy (sorry Shakespeare!) Rather, what this research suggests is that the configuration of one’s iris is incredibly complex and unique, just as is one’s personality.
While the results of these studies are by no means conclusive, they are exciting in the sense that eyes have been long considered as a window to one’s soul – the part of your body that is most likely to reveal your thoughts and feelings. Long live mysterious green eyes!