I think the most likely explanation for similar cultural practices is cultural diffusion.
Multiple origins of cultural ideas are possible, of course. I would yield to every well-documented case.
Still, after years of being impressed with similar practices in many places, I have been drawn to the ultimate lumper idea: cultural diffusion is the most likely explanation of similar cultural practices.
[RE: Lumper - There are two kinds of people: lumpers, and splitters. I am a lumper. I am interested in connections among people and cultures.]