The Mystery of Melanin: Why Our Skin Is Brown and Our Eyes and Hair Can Be Any Color

Have you ever stopped to wonder why the melanin in our skin only comes in various shades of brown, yet the melanin in our hair and irises can come in a multitude of colors? This fascinating inquiry delves into the fascinating world of melanin and the genetic and chemical processes that govern these differences.

Understanding the Three Types of Melanin

There are at least three types of naturally occurring melanins: eumelanin, pheomelanin, and neuromelanin. Each type has its unique chemical composition and physical properties.

Eumelanin is responsible for black and brown pigmentation in the skin, hair, and eyes. It absorbs most visible light due to its high degree of conjugation, which makes it effective in protecting the body from ultraviolet (UV) radiation.

Pheomelanin, on the other hand, is responsible for the lighter red and yellow pigmentation. It contains sulfur-containing amino acids, which give it a more reddish hue compared to eumelanin. However, pheomelanin is less effective at protecting against UV radiation than eumelanin.

Neuromelanin is found predominantly in the brain and is not associated with pigmentation. Its purpose is more related to the function of nerve cells.

The Role of Genetics and Proportions

The proportions of these different types of melanins in the skin, hair, and irises are genetically determined. The genetic factors that influence melanin production and distribution are significantly complex, involving multiple genes.

For example, the OCA2 gene is responsible for the distribution of eumelanin in the skin and irises. Mutations in this gene can lead to variations in skin and eye color.

Moreover, the production and distribution of melanin are influenced by various factors, including the interaction of environmental factors with genetic predispositions. Prolonged exposure to sunlight can lead to an increase in eumelanin production, resulting in an “olive” or darker skin tone.

Neurodegeneration and the Connection to Melanin

Recent research has also shown that neuromelanin, while not primarily associated with pigmentation, plays a crucial role in the brain. High levels of neuromelanin are found in areas of the brain involved in movement, specifically in the substantia nigra and pars compacta of the midbrain. The accumulation of neuromelanin is associated with neurodegenerative diseases, such as Parkinson's disease, suggesting a link between melanin and neurological function.

Colors and Perception: Beyond Objective Reality

Colors are not objective things. There is no inherent “brown” or “black” other than the reflected light of the energy spectrum that our brains interpret and label. Our irises, like any other surface, are not a single, uniform solid, but rather a complex layer of cells that reflect and absorb light in various ways.

Interestingly, the perceived color of the irises can change due to environmental factors such as lighting conditions. This means that the same eye can appear different colors in different lighting situations.

Historical Changes in Human Appearance

Historically, it is believed that the shades of brown in our skin used to be more varied, similar to the colors of our irises. However, through the manipulation of humanity and nature over the centuries, the genetic diversity that once existed has been reduced. This phenomenon is particularly evident in certain populations around the world.

Today, there are few to none who recognize and understand the true historical diversity in skin color, a testament to the homogenizing effects of modernity.

Conclusion

The mystery of why our skin is brown and our eyes and hair can be any color lies in the intricate interplay of genetics, chemistry, and environment. By understanding the different types of melanin and how they interact, we can gain a deeper appreciation of the complex beauty of human diversity.