That's never actually been proven to be true. It definitely doesn't occur in "every living thing," and it's even questionable to its extent of endogenous production in mammals - example, we're not sold on if it occurs in neural tissue naturally or not yet, and for that matter where specifically in the body that it'd be utilized.
Yes, there's a decent chance of it being an endogenous neurotransmitter, but that's far from set in stone.
Without growth, what's the point?
Avid gardener and Ethnobotany enthusiast