According to the evolutionary theory, more advanced civilizations develop from primitive. However, archaeologists have been puzzled by civilizations that have appeared "full bloom" - very advanced, with no precursor civilizations. This includes even the first known civilization!

Intelligent extraterrestrial beings have visited Earth and made contact with humans in antiquity and prehistory. Proponents suggest that this contact influenced the development of human cultures, technologies, and religions. A common claim is that deities from most, if not all, religions are actually extraterrestrial in nature, and that such visitors' advanced technologies were wrongly understood by primitive humans as evidence of divine status.