there are a number of theories to explain why pygmies are so short. it has been proved that their height is hereditary, and is passed on from parents to children. it may have evolved because of the low ultraviolet light found in rainforests, where many pygmies live. this would mean that the pygmies would make less vitamin d in their skin. vitamin d helps the body absorb calcium, which is important for bones to grow. since the pygmies would get less calcium, they would have smaller bones and skeletons.