You may have heard of the Fermi Paradox, but if you haven’t, here it is in short: Given the high probability of alien life in the universe, why hasn’t anyone contacted it? If there are so many civilizations out there, probably much more advanced than we are because of how long the universe has been around (no offense universe, but closer to the point), why aren’t they doing what we’re doing? Are you sending out probes and desperately searching for other signs of life?

One idea is the Great Filter. The hypothesis is that before alien civilizations begin to leave their solar systems and colonize their galaxies, something will happen to stop them from doing so, otherwise we will see evidence of this in our own Milky Way. We don’t know whether this is a step from multicellular life to tool-using animals or whether it’s a step from where we are now to exploring the galaxy.

What makes this so interesting is that we don’t know if we have passed the “great filter” or if this will happen in the future. Could we have passed this filter while most single-celled life has not? Or will we, like other alien civilizations, destroy ourselves at some point before leaving Earth, perhaps through war or by exhausting our resources before we can escape?

Somewhat worryingly, some philosophers and scientists have suggested that this means that if we found life on Mars, it would have suboptimal consequences for our position in relation to the Great Filter. Oxford University philosophy professor Nick Bostrom said he hoped the search for extraterrestrial life would be in vain. In a paper published in MIT Technology Review in 2008, Bostrom argued that if we found very simple life forms, we could conclude that the filter originated somewhere. after that this point in life. If we find multicellular life, we narrow down where the Great Filter could form.

Bostrom believes that to narrow down the filter, we need to look at life on Earth and see what steps are unlikely. “One of the criteria is that the transition must occur only once,” he wrote. “Flight, vision, photosynthesis, and limbs have all evolved many times here on Earth and have therefore been overlooked.”

He also argued that evolutionary features that emerged long after prerequisites were met, such as the primitive emergence of life, indicate that this evolutionary step was unlikely. The transition from animals to humans occurred in a relatively short period of time in geological terms, making it a poor candidate for the Great Filter event.

He believed that if we found evidence of vertebrates on Mars (highly unlikely, but we can dream!), this would be terrible news, because it would indicate that much of the Great Filter was still in our future and we would have to do it. We face the possibility of extinction before we reach the technological maturity to travel the galaxy.

“Such a discovery would be a devastating blow. It would be the worst news ever to hit the front page of a newspaper,” Bostrom wrote. “So I hope that our space probes will find dead rocks and dead sands on Mars, on Jupiter’s moon Europa, and everywhere our astronomers look. This will preserve hope for a great future for humanity.”

So while there are many other possible solutions to the Fermi Paradox that are worth looking at, if you’re interested in that sort of thing, if Bostrom is right, then finding evidence of advanced civilizations is good news, but finding that the false stages of life evolved independently is about as far as we can get in our own Solar System system. It would be bad news.