J-Shaped Spine Upper Back Curvature - How Many Degrees?

Hello,

I originally posted this message under "back conditions," but now realize that this question probably should have been posted under "General questions." 

In the West today doctors define a "normal" posture as having a kyphotic upper back curve of 30 - 35 degrees (below 15 degrees is considered flat-back, and above 50 is considered kyphosis).  As Esther Gokhale has reported, people who live in nature and squat have a straighter posture, with a more J-shaped spine overall.  Does anyone know what those people's normal kyphotic upper back curve is (ideally the mean and range)?  

Best,

Charles431