It's highly probable that life exists outside of Earth. However, that probability alone is not enough to say definitively that aliens do or don't exist. There is no evidence that I'm aware of that proves we've been visited by aliens. It's possible that the organic materials which developed into lifeforms on Earth were seeded by asteroids and comets. It's really all just speculation. If aliens do exist, they would probably come with a wide range of intelligences...From amoeba to superhuman. If some have been capable of visiting us, they would most certainly be smarter than us. We haven't even figured out how to send manned missions to some of the planets within our own solar system. If we are ever discovered by extraterrestrial beings before we discover them, let's just hope they are benign.
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