Murder Theory (The Naturalist, #3)

by Andrew Mayne

don’t know if the craving is coming from my brain or the trillions of bacteria in my stomach that have learned to trip my nervous system by producing their own dopamine triggers. They’re really that clever. There’s frightening research that some cases of obesity could be caused not by a fault in your genes, but by your gut microbes clamoring for the kinds of foods you shouldn’t be eating.

We humans have genes free-riding in our genome that were left behind by viruses that somehow managed to get their code written into the master program.