A new Mum recently came in for her annual eye test and brought her baby boy with her. He was absolutely adorable (and very well behaved!) with his pinch-worth chubby cheeks and gorgeous baby blues. His Mum asked whether his eyes would stay blue or change like lots of other babies eyes do. Then she asked, ‘Why do babies’ eyes change colour?’
This is an interesting question! Many newborns sport blue eyes for the first few months of their lives but end up with hazel or brown eyes when they get older. If a baby’s eye colour is determined by genetics, how can the colour change given that the child’s genetics remain the same?
It is true that it is our genetics that determine whether we have blue or brown eyes. So when a baby is born, genetics has already predetermined the eye colour. However, the amount of pigment required to achieve said colour doesn’t finish accumulating and depositing in the eye until after birth. Melanin, the pigment in the iris, is what gives the eye colour – less melanin equals blue eyes, more melanin equals brown eyes. Only once a baby is born does the body start producing the genetically predetermined amount of melanin to give the eye colour.
So can you guess what colour your baby’s eyes will end up? Well if your baby has two blue eyed parents, he or she will almost definitely be blue eyed too. However even if both parents are brown eyed, your baby may still have blue eyes if the parents have the genes for blue eyes in their DNA. Genetics is a wonderfully complicated and incredibly interesting field of study – not just in terms of iris colour, but also for risk of eye disease, myopia (short-sightedness) and other inherited eye conditions.
Brown, E.J. (1906). The Embryology Anatomy and Histology of the Eye. Chicago: Hazlitt & Walker. 1906
Snell, R.S., M.A. Lemp. (1998). Clinical Anatomy of the Eye. Oxford: John Wiley & Sons Ltd. 1998