I don't know much about this topic, and I was asked a question that required more research, so I thought I'd share with you some research I found on African hair types.
Thanks to Isis/Diana for asking me about the research materials I used in the post on African hair! I've altered the post to reflect that I can't confirm the information about increased pH level in African hair (and couldn't find it on my notes in my hair chemistry notebook), and I've added a few things and some references. If you find something that doesn't make sense on the blog, write to me at email@example.com. (And here are some suggested ways to approach me if you think I'm wrong!)
Analysis of structural changes in bleached keratin fibers (black and white human hair) using Raman spectroscopy - To investigate the influence of bleaching treatments on keratin fibers...From these experiments, we concluded that the melanin granules including metal ions act as a decomposition accelerator for the oxidizing agent, thereby leading to a higher level of disulfide (–SS–) group cleavage in the black human hair compared with that of the white human hair.
Apparent fragility of African hair is unrelated to the cystine-rich protein distribution: a cytochemical electron microscopic study - A feature of black African hair is an apparent increased fragility of the hair shaft compared to other ethnic groups (as measured by the tensile force needed to break the hair fibre). [T]here is no abnormality in their distribution in black African hair shafts compared to the other ethnic groups. Therefore, the excessive structural damage observed in the African hair shafts is consistent with physical trauma (resulting from grooming) rather than an inherent weakness due to any structural abnormality.
Hair breakage (a PDF). Lots of good information in here!
African Hair Morphology: Macrostructure to Ultrastructure (PDF): Great information about how African hair grows and breaks.
Fragility of African hair (PDF). The conclusions? That the "excessive structural damage observed in African hair is consistent with physical trauma (resulting from grooming) rather than an inherent weakness due to any structural abnormality."
Here are the proceedings of a L'Oreal conference in Africa about hair and skin, and it's really interesting reading!