Only largely among most vertebrate animals (not all), and among some groupings of invertebrate animals (not all). But not all animals have brains.
The following animals have no brains, and they are all marine invertebrates:
- Jellyfish
- Oyster
- Clam
- Sea urchin
- Sea anemone
- Starfish
- Sea squirt
- Sea lilie
- Coral
- Sponge
These are the only ones that I can remember right now, creatures that have no brain. However, except for the last one in that list above - the sponges, the rest have some sorts of set of connective neurons, not nerve tissues, but what biologists called NERVE NET.
The sponges are the only ones that don’t even have nerve net.
It far too complicated for me to explain what a “nerve net”, so you would have to either ask someone else, or look it up, read & learn it yourself.
Plus, intelligence are largely learning processes, therefore not the trait that can be passed on genetically.
Plus you are ignoring the rest of the eukaryotic kingdoms, like plants, fungi and protists, and domains of prokaryotic microorganisms, such as the bacteria and archaea. None of these non-animals have brains too. So intelligence isn’t a trait for these organisms, therefore intelligence isn’t really imperative among prokaryotes and among the majority of eukaryotes.
why are you ignoring other these non-animal organisms?
lastly, I have mentioned central nervous system and nerve net before, so clearly you have ignored my earlier reply on the subject intelligence and consciousness.