Honestly, I think it has to do with human biology and heat.
Heat escapes from our heads, hence why we wear caps in the winter, to contain the heat. Heat rises. Afro hair is tightly coiled because of evolutionary adjustment to hot weather in Africa. So, it makes sense, then, that if the heat is rising upward and our hair has the tendancy to coil tighter when encountering heat, the "looser" hair would be that in the back, since it misses this "heat passage"
My most tightly coiled patch it dead center in my head at the top. My hair gets looser and looser as you move away from that patch. Maybe thats the place my body heat travels upwards and escapes from?
