How did the blue eyes evolve in humans?|Curiousminds97

So the eye colour is determined by two distinct
factors: the pigmentation of the eye’s iris and the frequency-dependence of the scattering
of light by the turbid medium in your iris. In humans, the pigmentation of the iris varies
from light brown to black, depending on the concentration of melanin in the iris
The iris is a thin, circular structure , which controlls the diameter and size of the pupil
and thus the amount of light reaching the retina. The color of the iris gives the eye
its color So how did the blue eye’s evolve in humans?
There is no blue pigmentation either in the iris or the ocular fluid. Dissection reveals
that the iris pigment epithelium is brownish black due to the presence of melanin. Unlike
brown eyes, blue eyes have low concentrations of melanin in it.So the longer wavelengths
of light tend to get absorbed by the dark underlying epithelium that acts as a barrier
to protect the cornea,, while shorter wavelengths are reflected and undergo Rayleigh scattering
in the turbid medium of the stroma. So Rayleighs scattering is a phenomenon in which elastic
scattering takes place of light or other electromagnetic radiation due to particles which are even
smaller than the wavelength of the radiation itself.
So the same phenomenon accounts for the appearance to the sky to be blue. In 2008, new research tracked down a single
genetic mutation which gave us blue eyes.Originally, we all had brown eyes, a mutation in the HERC2
gene,subsequently resulted in the reduction of melanin production, As we learnt earlier
higher melanin concentration gives you brown colour and lower gives you blue. The authors
suggested that this mutation may have taken place in the northwestern part of the Black
Sea , In effect, this mutation turned brown eyes
to blue. If the gene had been completely shut down, our hair, eyes and skin would be melanin-less,
a condition known
as albinism.

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