Why do people have different colors
Why do people have different hair colors?
People invest a lot of time and money into the look of their hair. Although we know chemically why hair is colored the way it is, much remains to be learned about the genetics behind hair color.
And the question of why people exhibit the variety of natural hair colors we see, from blonde to black to brown to red, could be key to part of our evolutionary history.
According to geneticist Luigi L. Cavalli-Sforza, the variety of hair colors we see in people today may be the result of a force known as sexual selection. Like natural selection, sexual selection is a force that shapes evolutionary trajectories. In contrast to natural selection, however, sexual selection specifically focuses on traits related to partner acquisition.
According to this theory, the dissimilarity of hair color may be the result of randomly more noticeable hair colors, and these rare colors give their owners an edge when it comes to attracting a mate. Better success in finding a mate would have meant better success in producing offspring who would then carry the genes for new hair colors and pass them on to their own offspring.
Hair color is determined by two types of pigments, eumelanins and pheomelanins, which together create all of human hair colors. (“Melanin” is the basic term for any pigment or coloring in hair or skin.) Phaeomelanins produce the color red, and eumelanins can produce either black or brown pigments.
Eumelanins determine how dark or light the hair will be. A person who produces very little brown eumelanin has blond hair. Low levels of black eumelanin lead to gray hair. Lots of black or brown eumelanin will result in darker hair.
Everyone also has some pheomelanin (reddish) coloring in their hair. A person with real red hair produces high levels of pheomelanins.
Phenotypes are the physical expressions of a person's genotype or the unique sequence of DNA that determines a person's makeup. However, it is not always easy to map physical features directly onto the genes that produce them because genes often interact in complex ways. Genetic complexity is the case with hair color, the underlying basis of which is not clearly understood. Theories of genetic control of hair color include a multigene location of control and a dominant / recessive gene relationship.
Dominant / recessive gene relationship
In a dominant / recessive gene relationship, a child must inherit two copies of the recessive allele for the gene (one from each parent) in order to express that trait (such as hair color) in their phenotype (or appearance). A dominant / recessive model would help explain how two dark-haired parents could produce a blonde child, but this model cannot fully explain all of the variations in human hair color seen today.
Hair and aging
Simply put, the hair is gray when the hair follicles stop producing melanin, especially the eumelanins and pheomelanins discussed above. Each of us is born with a limited number of pigment cells in our follicles. The exact number is genetically determined. With age, pigment production decreases and then stops, resulting in gray hair. Poor diet, smoking and certain diseases can accelerate pigment loss and lead to premature graying.
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