Now isn't that interesting?
"How can sexual satiation drive mates apart? When scientists looked into the brains of mating rats, they discovered that a neurochemical called dopamine (the "I gotta have it!" substance) was behind the phenomenon of mate fatigue. As a rat copulates repeatedly with the same partner, less and less dopamine is released in the reward circuitry of its brain.
Yet when a novel potential mate shows up, dopamine surges again. It's the same mechanism that causes you to say "yes" to a sugary, fat-laden dessert even when you're full of turkey and mashed potatoes. Dopamine surging in your reward circuitry can override your feelings of satiety, regardless of what your rational brain may think about overeating or infidelity. Surging dopamine is a "yes!" while low dopamine is a "not so much." As we'll see in a future post, dopamine also naturally drops after orgasm, which plays right into this phenomenon. Our genes can be heartless puppeteers."