Are they in they in heavy tree'd areas though? I thought of that and other equatorial areas often have tree canopies, so human heads aren't necessarily getting bombarded with sunrays as often or as direct.

I think there is something to the combination of dry climates (resulting in less vegetation), lots of sun, and kinky / curly hair.
High Density, High Porosity, Medium Texture, 3B with some kink

Lo-Poo: No Preference
Co-wash: CJ Smoothing Conditioner
RO: CJ Strengthening Conditioner - HG
LI: CK Satin Roots
Styler: CK Coil Jam
Other Likes: Castor Oil; CK Twist Whip, MD CSC
Dislikes: Wheat Protein; Aloe LIs or Stylers