Here's why:
* Genetics: Genes that code for darker hair (specifically, high levels of eumelanin) are dominant. This means that if you inherit even one gene for dark hair, you're more likely to have dark hair. In contrast, genes for lighter hair colors are recessive, requiring you to inherit them from both parents.
* Geographic Distribution: Dark hair is more prevalent in populations native to regions with higher levels of sun exposure. Melanin, the pigment that gives hair its color, also helps protect the skin and scalp from the harmful effects of ultraviolet radiation. Therefore, natural selection has favored darker hair in these regions. The majority of the world's population lives in Asia and Africa, where dark hair is most common.
While specific percentages can vary slightly depending on the study, the general trend is clear: dark hair colors are significantly more common than lighter hair colors like blonde or red.