Hmmm... This thread just keeps on giving! 😀
Aliens - animal, plant or something totally different?
Multicellular bacteria??? Don't know if you guys know much about cellular biology but on the off-chance you don't, I'd like to give you a crash course ( 😉 ) to present a point that I think is relevant here. Please excuse me if you're already familiar with most / all of what follows though...
Cells contain a 'soup' - cytoplasm. In the cytoplasm, there are various structures - organelles - that perform key roles in allowing the cell to live. You have in this world two types of cell, prokaryotic (bacteria and their ilk, real basic stuff) and eukaryotic (complex life forms).
Now, in complex life you have 2 organelles that could be of great interest here: chloroplasts (used by plants to convert light, carbon dioxide and water into sugar and oxygen) and mitochondria (used by ALL complex life to burn sugar to produce energy).
The incredible thing about these two organelles is how they came to be present in eukaryotic cells but not in prokaryotic cells. Last I heard on the subject (20+ years ago), the most popular theory on the evolution of these organelles involved them both starting out as bacteria that were at some point engulfed by other bacteria-like cells (/ bacteria) and, with time / generations, incorporated into them.
This enabled eukaryotic cells to further evolve and evolve quite spectacularly into most of the life forms visible to the naked eye.
Life also went from unicellular to multicellular (but I'm pretty sure some prokaryotes managed to achieve this also, so we won't go there, I think...)
Now the point of all this:
Can complex life (ie. 'intelligent life' that could feasibly exist extra-terrestrially) arise without mitochondria? 'Mitochondria' that came from somewhere other than bacteria? These questions make me want to bang my head against the nearest wall. 🙂
The ultimate point:
Everyone is familiar with plants, animals, fungi and bacteria (we won't go near viruses as they're pretty alien themselves!!!). But then there are others (if I recall correctly) that have been reclassified over the years including protista and protozoa (again, iirc).
So, if there are aliens and on the off-chance they're lightyears ahead of us in every sense of the word, could they be something other than animal that maybe would make them totally benign like plants (other than the relatively few carnivorous ones of course) or relatively benign like fungi.
There could be symbiosis (different life forms living together as one to their mutual benefit, to the point where the division lines get very blurred indeed) too.
Can a non-terrestrial plant-like life-form have a brain??? Maybe, I'd say (hypothetically).
We know there's at least one route to intelligence, the path unicellular organisms followed all the way to us. But there could be so many worlds teaming with life so basic that only a microbiologist could find anything of interest to play with. And I do worry that's a circular argument (first sentence, this paragraph).
In these worlds, in no way could we take the evolution of intelligence for granted. I reckon. And I do think that some form of carnivorous lifestyle would be a pre-requisite. But no way can i be certain.
Sorry for all the long reads 😉 I was going to discuss dentition and diet regards vegetarianism in particular but I'll save that for another forum maybe? 😉