response: I have no idea, but I can tell you that brown hair has more eumelanin and less pheomelanin.
original_response: Brown hair is this shade due to having high levels of the dark pigment eumelanin, and lower levels of the light pigment pheomelanin.
history: I have brown hair unlike my sister who is blonde Oh, interesting. Were you aware that brown hair is second only to black in commonality? yes.  it is strange - I wonder where red hair comes from
knowledge: It is characterized by higher levels of the dark pigment eumelanin and lower levels of the pale pigment pheomelanin.