And because physical traits are inherited independently of one another, knowing the range of one trait does not predict the presence of others. For example, skin color varies largely from light in the temperate areas in the north to dark in the tropical areas in the south; its intensity is not related to nose shape or hair texture.
This reminds me of the theory that human life itself originated in africa and as people migrated to different places with colder or hotter temperatures, they adjusted and generation after generation became lighter