Here's one of those curiosities I've never been able to get out of my brain. This is more a question about the root mythology than D&D.
In D&D, you have this elemental assignation of the Genies - Djinn for Air, Efreet for Fire, Marid for Water. The 'Earth Genie' is much less consistently defined - Pathfinder uses Shaitan, older editions use the Dao.
This obviously stems from the vague Elemental connections mythology gives to the Genies - Marids are associated with the open sea and ships. All Genies are made of 'Smokeless fire', so that explains the connection that the Djinn and Efreet have with Air/Fire. (as Fire tends to be associated with evil in Western thought).
The Earth Genies seem to have the least connection to Arabic mythology - Shaitan is a specific Ifrit analogous to the Christian devil, made out of air and fire like all other Djinn. I can't find any Arabic source for the word 'Dao.'
In the Quran, no race of Djinn is associated with the Earth, but Humans are made out of clay.
In Arabic Mythology, are Humans intended to be the "Earth Genies?" And why has this been universally ignored in D&D?