In Oregon, populations of newts just 10-15 miles apart are on opposite ends of the extreme: one population of newts has just trace levels of TTX, but in the other population one newt has enough TTX on average to kill up to 30 people! The evolutionary arms race is chugging ahead full steam in one population, but cruising at a snail’s pace in the other. Can one evolutionary battle influence others close by? If gene flow occurs between populations engaged in these two different battles, it could result in a mismatch of newt toxicity and snake resistance. For example, imagine populations of very toxic newts and very resistant snakes living in one creek (creek 1), while across a ridge lies another creek housing populations of not-very-toxic newts and not-very-resistant snakes (creek 2). The newts cannot easily cross the ridge separating the two creeks — but very occasionally, they do. If a very toxic newt journeys to creek 2, home of the not-very-toxic newts, it could stay and start a family. Some of the toxic newt’s offspring might be more toxic than any of the not-very-resistant snakes could handle. Those newts would survive to have more offspring and the genes for extreme toxicity would spread.

You might think that the not-very resistant snakes in creek 2 would develop resistance, that the arms race in creek 2 would intensify, and the races in the two creeks would become more similar. This might happen, or it might not. It depends on the amount of variation in TTX resistance in the snakes at creek 2. If snakes have only low levels of resistance, no snake would have enough resistance to eat the now super-toxic newts and survive to pass genes on to its offspring. The less resistant snakes in creek 2 simply wouldn’t have enough variation to eat any of the more toxic newts and low resistance genes would be to no advantage to the snakes. In this case, those genes would not be favored by natural selection and the arms race would pause (or even backtrack) because of a power imbalance: highly toxic newts paired with low resistance snakes.