system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 what is it about alcohol/fermentation that makes it almost universally make everything drunk?

Insects get drunk. Elephants get drunk and everything in between. Is it the only chemical that has this type of effect on everything that consumes it?
gpt
Ok I’m not sure how ELI5 this answer will be, but I’ll try and I’m happy to clarify anything. 

Alcohol acts as an intoxicant for a few reasons. First it can pass the blood brain barrier in humans and virtually all mammals, and for animals without such a barrier it’s even easier for them to become intoxicated. Second, alcohol binds to receptors in the central nervous system that would normally bind to a substance called GABA, which is the primary way these nerve cells are down regulated in all mammals (and quite a few other animals besides). That depressive action is what leads to most of what we call getting drunk. 

Humans, and in fact all animals, share a LOT of the same basic genetic information which codes for metabolism, basic functions of life, and neurotransmitters like GABA. The use of things like chloride channels is almost universal, unless there’s a specific selection pressure to alter it (such as an evolutionary arms race with a neurotoxin). 

Alcohol is by no means the only things that is universally intoxicating either, for the reasons mentioned above about conservation of genetic material coding for basic functions. Some animals such as humans, which have an evolutionary history of eating overripe fruits, have evolved metabolic means (in the liver) to rapidly break alcohol down using an enzymatic pathway. For animals like elephants, they lack that same robust response, so a much smaller amount of alcohol will be more intoxicating to them, and leave them incapacitated for a longer period of time.