Human beings are aliens -

A top Blighty Boffin  claims that life was not born on this planet but travelled here on a giant comet and evolved when we could not get off it.

Prof. Chandra Wickramasinghe, astrobiologist at Cardiff University, which is famous for its temporal rift activity wrote in Cambridge University's international journal of space biology that everything on earth came from another planet.

"We are all aliens. We share a cosmic ancestry. "

He wrote the first "seeds of life" were deposited on Earth 3.8 billion years ago by comets These then multiplied and seeded other planets. We are thus part of a connected chain that extends over a large volume of the cosmos.

While this explains Celine Dion and why everyone in a Sci-Fi movie looks human, it does not tackle the problem of where the seeds of life came from, how they got on a comet, survived the freezing cold of deep space, and then built New York.  We think falling through a rift in space and time is a much better bet, although that theory means that all life started in Cardiff.