Genetic Variation Accounts for Infant's Altered Hair and Eye Color
In the journey of human evolution, one of the most intriguing aspects is the development of eye colour. From sun-rich Africa to sun-scarce northern regions, our ancestors' migration led to changes in eye and hair colour, particularly in melanin pigmentation and its use.
Newborns often exhibit light eye colours, such as blue or gray, due to low levels of melanin in the iris. As melanocytes, the pigment-producing cells in the iris, ramp up production over the first few months, the eyes can darken and change colour. This transformation is influenced by the amount of melanin deposited, which in turn determines the final eye colour spectrum. More melanin results in darker brown eyes, while less leads to lighter blue or green eyes.
By the age of 9 to 12 months, eye colour typically stabilises as melanin production reaches a steady state, and the melanocytes' activity levels off. Sunlight exposure during infancy can stimulate melanin production, influencing the darkening process, but this stabilising effect ensures the eye colour remains relatively fixed after about one year.
Genetics and environmental factors play a role in the exact timing and final colour of a baby's eyes. For instance, individuals born with blue or gray eyes may later develop green, hazel, or brown eyes, reflecting their genetically programmed melanin levels and environmental influences during infancy.
The evolution into a bipedal species has brought about other side effects. One such effect is the continued production of melanin in the eyes even after birth. In newborns, the distribution of pigment in the iris is not yet complete, and the level of melanin production is genetically determined.
Interestingly, the amount of light can affect the contraction and dilation of the eye muscles in newborns, which in turn impacts the distribution of melanin pigment in the eye and can cause changes in eye colour. This early birth has meant that humans have not fully adapted to the post-birth production of melanin, which prevents them from reaching their intended final form.
In conclusion, the colour of a human's eye is originally determined by a chemical called melanin. Understanding the evolution of eye colour provides a fascinating insight into our past and offers a glimpse into the complex interplay between genetics, environment, and development.
For a deeper exploration of the link between human migration patterns and changes in eye and hair colour, you can read the article here. Additionally, while one can estimate the eye colour of individuals in a family tree based on the known eye colours of the parents, this is not always straightforward.
- The development of eye color in humans, such as blue, gray, green, hazel, or brown, is primarily influenced by the amount of melanin, a chemical, in the iris.
- In the realm of health and wellness, understanding medical-conditions like changes in eye color during infancy can offer valuable insights into a baby's genetic predisposition and environmental factors that might influence their eye-health and overall development.
