ナショナルジオグラフィックのインスタグラム(natgeo) - 10月28日 12時31分

A photo for a book project in evolution...the beautiful eyes of Bella. The earliest human ancestors came from the continent of Africa, as #primates adapted and then branched off into many different species that eventually became our modern day human beings appeared.
Since the equator cuts directly through the continent of Africa, the countries there receive almost direct sunlight, with ultraviolet rays, and the warm temperatures it brings pressured for the natural selection of dark skin color.
Pigments, like melanin in the skin, protect against these harmful rays of the sun. Individuals with darker skin live longer and they would reproduce and pass down the dark skinned genes to their offspring.
#Naturalselection for the lighter eye colors are linked to the relaxation of selection for darker skin tones. As human ancestors began to migrate to various places around the world, the pressure for selection of dark skin color was not as intense.
These much higher latitudes afforded different seasons with much less direct sunlight , like near the equator, the selection pressure was no longer as intense, genes were more likely to #mutate.
The color of human #eyes is not dictated by a single gen many it of the other traits. It is instead considered a polygenic trait, meaning there are several different genes on various chromosomes that carry information about what eye color an individual should possess. These genes, when expressed, then blend together to make various shades of different colors. Relaxed selection for dark eye color also allowed more mutations to take hold. This created even more alleles available to combine together in the gene pool to create different eye colors.
#Sexualselection may also explain some of the different eye colors that have popped up over time. Mating, in humans, tends to be non-random and as a species, we are able to choose our mates based on desirable characteristics. Some individuals may find one eye color much more appealing over another and choose a mate with that color of eyes. Then, those genes are passed down to their offspring and continue to be available in the gene pool. @Robert Clark @thephotosociety

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