Postulated entities beyond Earth with a level of intelligence and comprehension at least equal to that of humans at the present time. While extraterrestrial intelligence is usually envisioned as an advanced civilization, populated by creatures that have evolved via Darwinian evolution on a planet vaguely similar to Earth, it could conceivably be artificial intelligence initially created by biological beings. Extraterrestrial intelligence is a subset of astrobiology, which encompasses all aspects of the existence of, and search for, extraterrestrial life. Astrobiology is sometimes referred to as exobiology or bioastronomy.