Taricha newts are one of the most poisonous animals in world, containing enough of the potent neurotoxin tetrodotoxin (TTX) to kill most predators that would dare to try to eat it. Their primary predator, Thamnophis garter snakes, have evolved resistance to TTX, and are in some cases able to ingest more toxin than a newt could ever produce. Extreme toxicity and extreme resistance have been shown to be the product of an ongoing coevolutionary arms race, with newts evolving ever higher levels of toxicity and snakes becoming more and more resistant. The origins of this arms race, however, have been mysterious. In my talk, I will explore the evolutionary reasons why snakes and newts first became coevolutionary combatants. By tracing the evolution of a single gene family, voltage gated sodium channels, which are the target of TTX, I will show how the current coevolutionary arms race builds upon over 100 million years of evolutionary changes in the ancestors of garter snakes and newts.