While there's no single gene that controls hair texture, research suggests that genes like TCHH, EDAR, FGFR2, and WNT10A play a significant role. These genes influence the production of proteins that affect the shape and structure of the hair follicle. A flatter, more elliptical follicle tends to produce curlier hair, while a round follicle usually results in straighter hair.
The distribution of different hair textures across various populations is the result of complex evolutionary processes, including adaptation to different climates and environments. For example, curly hair may have provided an advantage in hotter climates by creating an insulating layer that protects the scalp from the sun.