I read a long time ago an essay by Asimov that described what elements could support life as a building block and why most elements cannot. I didn’t fully understand that at the time but it was interesting to see why carbon based makes sense and some other random element does not work.
Similarly, I wonder if under different planetary conditions, smart alien life (so not single cell life) can be very tiny or very large, or if there are biological constraints that would restrict that size range regardless of basic setup.
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Brains are complex enough that you could easily have smaller *or* larger creatures with intelligence comparable to humans. There’s no biological reason why a creature the size of a small monkey or a creature the size of a whale couldn’t possess human intelligence.
That said, it’s unlikely for something the size of an insect to posses human intelligence because you can only make neurons *so* small and you need a certain number of them to create the necessary complexity for intelligence, because it’s not *just* about having a complex enough brain, it’s also about having the requisite organs and other support needed to furnish that brain with the nutrients and energy it needs. As a point of reference, your brain makes up about 20% of your daily calorie consumption, so it takes a lot of energy.
Intelligent life can vary in size, depending on the biological constraints of its environment
There are restrictions in the small direction. Cells could be smaller than ours but not arbitrarily small. Brains smaller than ours can be very smart, but there need to be billions of neurons or otherwise it will be limited in ability.
Those together mean there is some lower limit, but I can’t tell you where it is. Squids and birds on earth prove that with their comparably small brain and short lifespan that intelligence can work with very few ressources.
In the other direction there is no real limit. There are gigantic organisms even in earth, with tree colonies or gigantic mushroom networks that are basically just one organism that is connected. There is nothing that would rule out such a being evolving a form of intelligence
IF the biology was similar to Earth, intelligence would be linked to the number of connections in a “brain” this number of connections is easier in a larger brain.
While everyone else here is looking at earth-like biology, if we assume creatures could exist in all sorts of exotic forms throughout the universe there are still hard physics constraints on how much volume is required for a certain level of computational power
The [Bekenstein Bound](https://en.wikipedia.org/wiki/Bekenstein_bound) defines the maximum amount of information that can be stored in a given space
The [Bremermann’s Limit](https://en.wikipedia.org/wiki/Bremermann%27s_limit) defines the maximum processing speed in a given space
It may be possible for a human level intelligence to exist at bug size but as you get further down in size you’ll bump into those hard limits.
I sort of wonder if a eusocial species that is somewhat larger than ants, with highly differentiated castes, could develop into being a sort of sentient hive mind. Eusocial species are incredibly complex and intelligent on Earth, and I wonder if that social and intellectual structure could lead to a legitimately sentient species. I have no idea how that would work, but I imagine a highly ordered society, perhaps with innovation done by sepecific castes of the creature, or done by queens/kings of competing colonies. Something along the lines of the Formics in Enders Game, or the Trisolarans (who are the size of ants) from Three Body.
The short answer is that we really don’t know. If we imagine life to be similar to life on earth then there are limits. Limits on how small a neuron can be. Limits on how big an animal can be and still walk.
But we don’t know what we don’t know. If life on other planets is very different from life here. Maybe not even based on oxygen and carbon, then all bets are off on size limits.
What you are reading in this thread is based on what we understand today, based on our own examples.
The awesome thing about the unknown is that we can guess but there is no way to know. Could some microscopic critters on some distant planet have a different way to processing information that we cant even imagine today? Yes.
Could we be those microscopic critters to some other giant species that we cant even fathom? Also Yes.
Just as the dust mite (likely) cant imagine that humans put a robot on mars and gathered dust from a comet, we could be as equally small (or equally as dumb) to something else out there.
I just watched a kurgstaad video on why elephants can be shrunk or they would die, it actually is really relevant to this question.
Brains are complex things that need to have the cells within working at a relatively high rate of activity. The problem with that is that it generates a LOT of heat, heat you can only get rid of through the surface of an object. But as something gets bigger, the volume increases much faster than the surface area, so this heat exchange gets smaller and smaller as you get bigger and bigger.
Elephants deal with this by running their cells at a significantly reduced rate of activity, so they don’t generate as much heat. They also have more efficient heat dissipation systems than smaller animals, but that only can help so much. And with a brain, a huge brain that only works at a reduced rate of activity is no better than a much smaller brain that works at full capacity.
Of course, this assumes that a huge brain doesn’t evolve ways around this, through active cooling, modular processes, or something else. But given what we know, it seems reasonable to assume that the kind of cognitive functions we associate with humans can only come in a particular size of brain.
Probably a dumb question deserving of it’s own thread, but the body of this post had me thinking.
How would anyone *know* what elements or building blocks could support life? We know what those are here. But any alien life could have had completely different evolution. They could breathe chlorine and eat sulfuric acid soups for all we know. Or am I completely wrong?
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