As new parents, there’s an endless array of incredible moments you’ll experience as your baby grows. One of the most mesmerising changes to witness is the transformation of their eye colour. Those initial weeks of gazing into your baby’s eyes might reveal shades like brown, blue or grey, but have you ever wondered why those initial hues often defy expectations and evolve into a completely different colour? In this article, we’re going to delve into the enchanting world of baby eye colour changes to unravel the science and magic behind this captivating phenomenon.
Eye Colour
For the purpose of this article, eye colour refers to the appearance of the iris, the coloured ring immediately surrounding the eye’s pupil. The iris is like a diaphragm that controls how much light can enter the eye at any given moment.
While pigmentation of the iris governs most of our perception of eye colour, phenomena known as the ‘Tyndall effect’ and ‘Rayleigh scattering’ also have some effect on eye colour. Without getting too technical, that’s all about how light is scattered. To keep things simple, think of it as akin to why the sky is blue.
Let’s Bust the Blue Eye Myth
While it may be true that a good proportion of babies in Northern Europe are born initially with blue or grey eyes, this is not the case worldwide. Indeed, estimates∞ suggest that brown eyes are by far the most common eye colour in infancy when looked at globally. Blue is, however, the next most common.
So, How Does Baby Eye Colour Work?
Generally, nature is often guided by the principle of adaptation in order to optimise survival. The evolution of eye colour is no exception. In regions with high levels of sunlight, such as near the equator, darker eye colours are more prevalent. This is due to the increased need for protection against the sun’s harmful ultraviolet rays —with dark irises like brown ones having more protection than lighter irises, like blue, grey, or green. As humans migrated across different environments back in ancient times, changes in eye colour are likely to have provided advantages in terms of UV protection as part of adaptation to new habitats. The pigmentation and UV protection are accomplished through something called melanin.
Pigmentation: The Melanin Effect
The gradual transformation of baby eyes is closely tied to the production of melanin, a protein that’s secreted by a particular type of cell, called a melanocyte. The visible result is a pigment that’s responsible for colouring various aspects of our bodies, including skin, hair and, as it turns out, eye colour. As babies grow and their exposure to light increases, the production of melanin begins to intensify. This pigment infusion leads to subtle changes to the hue, gradually steering the eyes toward other colour shades. For example, eyes that start off in the newborn child as grey or blue may indeed eventually become something quite different, for example, green, hazel, or brown, as more melanin pigmentation is formed. It’s quite magical to see in such a small infant.
The Role of Genetics
While the colour journey is strongly affected by the melanin effect, genetics also play a significant role in laying the groundwork. While predicting eye colour solely on the eye colour of parents offers a fair estimation, eye colour inheritance is really a much more complex thing. At a cellular level, it involves one specific chromosome that affects iris colour and multiple genes, which control aspects like the initial amount of melanin in a newborn’s eyes and how the melanocyte cells behave in respect to further melanin production. With genes being passed to the child from both parents as well as the parents’ ancestors, the child’s final eye colour is not easy to 100% predict based purely on parental eye colour. Indeed, eye colour can sometimes ‘skip’ generations and surprise us all!
Blue eyes are the result of a unique genetic makeup. It’s thought∞ that a mutation in a gene called OCA2 in a single common ancestor 6,000 to 10,000 years ago, is responsible for this striking trait in all humans with blue eyes today.
How Long Does it Take?
The most remarkable shifts in eye colour tend to take place between the ages of six to nine months. By this time, the iris possesses sufficient pigment to offer a clearer glimpse of what the final eye colour is likely to be. Irises of infants can change colour up to about the age of three years old before it is fairly permanent. However, they can continue to change subtly throughout adolescence and early adulthood due to ongoing melanin production.
Heterochromia
Heterochromia is a rare condition, affecting less than 1% of people, where an individual has two different coloured eyes or two different colours in one eye. It can be genetic or caused by injury, disease, or medications.
We’ve learnt that the evolution of eye colour in infants is a captivating story of genetics, adaptation, and heritage. As parents, we have a front-row seat to this intriguing transformation, gaining fascinating insights into elements of human evolution, survival and the broader narrative of life’s journey on the planet.
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