人们认为最早的人类祖先来自非洲大陆。当灵长类动物适应并分支成生命树上的许多不同物种时，最终成为我们现代人类的血统出现了。由于赤道直接穿过非洲大陆，那里的国家全年都会受到几乎直射的阳光。这种直射阳光，紫外线和温暖的温度，为自然选择深色皮肤带来压力。颜料，如皮肤中的黑色素，可以抵御这些有害的太阳光线。这使得皮肤较黑的个体活得更长，并且它们会繁殖并将深色皮肤的基因传递给它们的后代。控制眼睛颜色的主要基因与导致肤色的基因密切相关。据信，古代人类祖先都有深褐色或近黑色的眼睛和非常黑的头发（这也是由眼睛颜色和肤色的相关基因控制）。尽管棕色眼睛仍然被认为是主要的整体眼睛颜色，但现在在全球人口中很容易看到几种不同的眼睛颜色。所有这些眼睛的颜色来自哪里？虽然仍在收集证据，但大多数科学家都认为，较浅眼睛颜色的自然选择与较暗肤色的选择放松有关。随着人类祖先开始迁移到世界各地，选择深色肤色的压力并不那么强烈。特别是对于现在是西欧国家的人类祖先来说，选择黑皮肤和黑眼圈不再是生存所必需的。这些高纬度地区提供了不同的季节，没有像非洲大陆赤道附近的直射阳光。由于选择压力不再那么强烈，基因更容易发生变异。在谈论遗传学时，眼睛颜色有点复杂。人眼的颜色不像许多其他特征那样由单个基因决定。相反，它被认为是多基因性状，这意味着在各种染色体上有几个不同的基因携带有关个体应该拥有的眼睛颜色的信息。这些基因在表达时，然后混合在一起，形成不同颜色的各种色调。对深色眼睛颜色的轻松选择也允许更多的突变。这创造了更多的等位基因，可以在基因库中组合在一起，创造出不同的眼睛颜色。
新加坡国立大学Essay代写：人类的血统
It is believed that the earliest human ancestors came from the African continent. When primates adapt and branch into many different species on the tree of life, they eventually become the lineage of our modern humans. As the equator passes directly through the African continent, the country there receives almost direct sunlight throughout the year. This direct sunlight, ultraviolet light and warm temperatures put pressure on the natural selection of dark skin. Pigments, such as melanin in the skin, protect against these harmful sun rays. This allows individuals with darker skin to live longer, and they will multiply and pass on the genes of dark skin to their offspring. The major genes that control eye color are closely related to genes that cause skin color. It is believed that ancient human ancestors had dark brown or near-black eyes and very dark hair (this is also controlled by genes related to eye color and skin color). Although brown eyes are still considered to be the main overall eye color, it is now easy to see several different eye colors in the global population. Where are the colors of all these eyes coming from? Although evidence is still being collected, most scientists believe that the natural choice of lighter eye color is associated with a looser choice of darker skin tone. As human ancestors begin to migrate around the world, the pressure to choose darker skin is not as strong. Especially for the human ancestors who are now Western European countries, choosing black skin and dark circles is no longer necessary for survival. These high latitudes offer different seasons, with no direct sunlight near the equator of the African continent. Because the selection pressure is no longer so strong, the genes are more susceptible to mutation. When talking about genetics, the color of the eyes is a bit complicated. The color of the human eye is not determined by a single gene like many other features. Instead, it is considered a polygenic trait, which means that there are several different genes on various chromosomes that carry information about the color of the eye that the individual should have. These genes, when expressed, are then mixed together to form various shades of different colors. Easy selection of dark eye colors also allows for more mutations. This creates more alleles that can be combined in a gene pool to create different eye colors.