OK, we agree. Human behavior is regulated by neurotransmitters that were designed by a billion years of evolution. It is tyrosine, a common amino acid found in many foodstuffs, with a few little changes at one end. Dopamine alone is not enough to give us a rush.
Dopamine is a key that opens a lock.
The lock is called a receptor, a large protein that sits on the surface of brain cells. The receptor is recognized by dopamine but by no other chemical, just like a lock can only be opened by the correct key. When the dopamine snuggles into the waiting receptor, the tumblers turn. Inside the brain begins a series of chemical reactions. When you cut through all the jargon, evolution theory is simple and elegant.