Mankind has always wondered where he came from, and he has always looked at the night sky with wonder. Is there a reason for that other than its' beauty, and man's natural sense of curiosity and wonder? In the 1970s, popular writers such as Erik von Daniken, in books such as Chariots of the Gods, put forth the theory that mankind did not develop from a small mammal to the intelligent being he is today solely by natural selection, as Darwin maintained. According to von Daniken, and others like him, the Earth had been visited in the distant past by intelligent visitors from other worlds, and these visitors were responsible for the creation of such wonders as the Pyramids and Stonehenge, as well as for setting mankind on the path of evolution. In a sense, he maintained, these interstellar visitors were gods, and were probably responsible for the pantheon of gods in the ancient world, such as the ones on Mount Olympus. They may even have conducted genetic experiments, combining ancient humans with other animals living on earth to create totally new life forms. The half-man half-beast creatures depicted by the ancient Egyptians were therefore not just art, but depictions of actual living beings.
What are we to make of this? It is certainly possible that the Earth may have been visited in the distant past by intelligent beings from other worlds, and that these beings may have experimented with us, much as we are currently conducting genetic experiments to clone sheep and other animals, and to combine the DNA from different life forms to create totally new ones. It is certainly possible that these extra-planetary visitors, if any, may have looked upon our distant ancestors in a similar fashion. And it is certainly noteworthy that various ancient civilizations in different parts of the world seem to have had so many common histories and myths, such as that of a great flood, and indeed that of being visited by otherworldly beings. So there is nothing about the idea that we were visited by ancient astronauts in UFOs that is inherently impossible.
However, I believe that to attribute all, or nearly all, of human progress to the influence of extraterrestrial visitors, as von Daniken and others like him do, is to sell the human race short. It is entirely possible, and even likely, that humans of thousands of years ago may have been far more technologically advanced than we previously believed. There may have even been civilizations that were even more advanced than we are today, such as the myth of Atlantis, which may not have been just a myth. The Vedic civilization that existed in ancient India five or ten thousand years ago had knowledge that we still do not possess, such as the power to levitate, and the ability to use sound as a weapon. Probably as time goes by and we learn more about our ancient ancestors, there will probably be less need to ascribe their accomplishments to ancient astronauts.