I’m not convinced it does. The best we can really say is that this is one possibility.
Talk about quoting out of context, why snip my sentence there when the next word is “unless”?
All of the scientific evidence shows that we are unique in the universe. That’s because we have so little evidence. We have scratched the surface of the Moon and Mars. We have brief glimpes of Venus below the atmosphere. That’s about it. Everything else is speculation.
The best scientific evidence would consist of actually going to another solar system and finding life there. Even if we detect really convincing life-signs on a distant planet using remote sensing, these life-signs might be a false positive caused by some natural physical process or other that we don’t anticipate.
Even then we might never be able to falsify the proposition that life exists on other worlds. If we examine a thousand planetary systems and fail to find life, we might find life in the thousand-and-first system, and so on.
The search for extraterrestrial life might be an indefinitely extended venture, and we might never be able to find definite disproof of the existence of such life. If we don’t find life elsewhere in the Milky Way it might be found in Andromeda, and so on.
Not completely, some scenarios are more likely than others. For example, it’s highly unlikely that life is uncommon, but on average quickly develops into complex and then intelligent life, as this would make the Earth a doubly atypical case. It’s also likely that the ratio of complex to bacterial life is low, but we have no idea how low.
But yes, what is needed more than anything else is evidence.
My reservation applies notwithstanding your “unless” clause.