Question

Has there been any evidence that human life has ever lived on any other planet besides Earth?

Not that we know of. Given the fact that humans have only been on Earth for couple hundred thousand years (a blink of an eye compared to other species’ time on the planet), the likelihood that a subset of our species managed to develop the technology to escape it seems pretty incredible. The reverse scenario—that humans actually evolved elsewhere and colonized Earth—is not impossible, though fossil records suggest otherwise. Similar ideas to yours have been part of an ongoing interest in the SETI Institute (Search for Extraterrestrial Intelligence) for over a decade. For an overview of current thinking concerning intelligent life elsewhere in the universe, see the SETI website created for the scenario of contact via the detection of radio signals at http://www.seti.org/science/principles.html While this document has no legal status, it is endorsed by almost all groups engaged in serious ET searches. Similarly, there has also been some discussion about the desirability of replying to an extraterrestrial signal--if some day we detect one. A draft document on this topic can be found at http://www.seti.org/science/iaa.html Anna Lee Strachan, NASA Astrobiology Institute
May 1, 2002