«It’s not much of an overstatement to say that your gut bacteria are a large part of what makes you you, psychologically. Transfer gut biota from one animal to another, and you transfer personality traits as well.

Think about that. You can literally transplant personality traits via feces. To that extent, we all have shitty personalities.

How does it work? For starters, your gut has a mind of its own: a standalone neural net with the computational complexity of a cat brain (no surprise there—cats are basically stomachs sheathed in fur anyway). Your gut microbes pull its strings by feeding it a complex cocktail of hormones and neurotransmitters; gutnet, in turn, tugs at the brain along the Vagus nerve. (Gut bacteria also have a more direct pipe into the brain via the endocrine system. Most of your brain’s neurotransmitters—half the dopamine, most of the serotonin—are actually produced in the gut.)
Via such avenues, your gut bacteria influence the formation of memories, especially those with strong emotional components. They affect aggression and anxiety responses by influencing neuroinhibitors in the prefrontal cortex and amygdala (which is responsible for fear, aggression, and the intensity   of one’s response to personal-space violations). You can make rats more or less aggressive by tweaking their gut biota.»
— Peter Watts is an angry sentient tumor
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