Ontons
Ontons, also known as Reality Memes are a function of Darkness. When universes are adjacent (perhaps not physically but semantically or ontologically or symbolically), the function of Darkness is to project the strongest influences between realities.
As genes shape biological evolution and memes shape the evolution of cultural thought, the Onton shapes the development of a universe.
This is why the humanoid shape is so common across realities. It is an Onton which has spread to adjacent realities and the adoption is so common it serves to spread it further.