Mine is probably the most boring: There are many intelligent species in the universe. Faster-than-light travel, however, really is simply impossible, meaning that there cannot exist a truly interstellar civilization. So while some species have probably settled solar systems other than their own through generation ships, suspended animation, time dilation, or whatever, their range of expansion is limited. This means that encounters between species of different planets are rare. Humans will most likely never contact any intelligent alien species, at most one or two. We might, however, discover evidence of their existence through telescopes or something.
Yeah, that’s kind of more like it. We can’t really estimate the intelligence of extinct species that well aside from looking at brain size and other physical circumstantial evidence, but I’m extrapolating from our current and growing understanding of intelligence in non-human animals like dolphins and corvids. We’re increasingly realizing that these species are much smarter than we had previously thought, and the toolmaking, memory, and self-recognition displayed specifically by magpies (I think) means that these traits can evolve outside of mammals.
I’m of the opinion that ‘being human-level smart’ is not something that’s only popped up in humans, but merely that our hominid ancestors were the first to combine that with other relatively rare features like opposable thumbs to allow for unprecedented tool use, and then things just happened from there.
