Can't we use the argument that with 8.7 million species, what are the odds, that we are number #1? Why do we assume we are #1, and not some lowly species with not even the slightest idea of what apex is above us.
Sentience/consciousness is a hard thing to define/study, but that doesn't stop people from trying.
Outside science, it's a fun idea to think about. For example, the obligatory Hitchhiker's Guide to the Galaxy quote: "For instance, on the planet Earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much—the wheel, New York, wars and so on—whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man—for precisely the same reasons."
Apes, monkeys, octopuses and crows have been observed making use of tools, or even making tools with which to make tools. Measured neural activity in crows suggests self-reflection and high level cognition [1]. Lots of species (including elephants, dolphins, and even pigeons) can pass the mirror test, suggesting an awareness of self.
There's controversy about how to measure or interpret animals' subjective experience, but I think it's pretty clear at this point that human intelligence compared to animal intelligence is a difference of degree, not of type.
[1]https://www.smithsonianmag.com/smart-news/do-crows-possess-f...
Over time, domesticated wolves figured out that humans were more advanced because they consistently had access to food and shelter while wolves had to hunt for it. By adapting their own behavior to fit in with the superior species, we wound up with today's dogs who largely choose to be servile because it's advantageous to them. Isn't that an example of recognizing a higher species and submitting to it?
The "how they know, how we know" question is clear, too. Dogs knew we were smarter because of what we were able to accomplish and provide. If a "superior" alien race showed up and could do stuff we couldn't, we'd think they were smarter, too.
Language and adaptability play a big part, too. Cetacean language certainly helps them survive, and so does primate language. But human language went far beyond any other species and allowed man to cooperate and coordinate adaptations, like creating a building and heating it to survive the cold. Or inventing transportation to move to a more desirable living space. No other animals have pulled that off at that level.
I personally believe that if we assume humans experience some form of high-level consciousness, we must assume that all/most species do too. They have different neural networks, different sensory organs, different communication mechanisms, but they do not LACK these things. An octopus or a bat will experience the world in a vastly different way to ours, not higher or lower. I'd like to see the burden of proof go the other way - what evidence do we have that humans' neurobiology is uniquely suited to consciousness while every other species' is not?
Of course we are superior in many aspects, but we're not "higher" in the general sense. We _are_ animals, we're next to each other.
> why do we assume humans could consciously conceive of whatever life-form is above us?
Can we conceive how to be a "lower" form of consciousness? Or even a different human? For example, we have no idea if everyone perceives colors the same way. We know that butterflies can detect UV light, but is it "mapped" to the same color range that we perceive, or can they perceive colors that we can't even imagine?
Minor changes in neural regulation can provide substantial differences in perception. That's saying nothing about trying to understand the perspective of a completely different species, which the differences are even greater
On top of this, all of our definitions are generally based on human experience
I think part of consciousness is being constrained by a certain perspective, and so all animals like us see the world from that anthropomorphic (or catomorphic) lens. I mean we communicate with animals using human language and vice-versa.
Animals have brains and nervous systems, form communities and social relationships. And a lot of them use tools as well. This is taught in middle-school biology.
Get a pet, you will quickly realize how similar we all are.