This study has shown that it is possible to classify the various hair types found worldwide into eight main groups. The approach involves objective descriptors of hair shape, and is more reliable than traditional methods relying on categories such as curly, wavy, and kinky. Applied to worldwide human diversity, it avoids reference to the putative, unclear ethnic origin of subjects. Briefly, a straight hair type I is just that, and whether it originates from a Caucasian or an Asian subject is not at issue. The hair types defined here also more adequately reflect the large variation of hair shape diversity around the world, and may possibly help to trace past mixed origins amongst human subgroups.