“It takes all the running you can do, to keep in the same place,” says the Red Queen in Lewis Carroll’s Through the Looking Glass. If I were an economist or sociologist and psychologist, I’d talk about the struggle of making ends meets in this economy. But I’m a biologist, so I apply her royal words to the natural world. I’m not the first to do so: the Red Queen Hypothesis, an evolutionary theory about how species that interact must adapt, was inspired by that very quote.
The Red Queen Hypothesis hinges on the idea that biotic parts of the environment (think living organisms, like plants, microbes, animals, etc.) play a role in the evolution of a specific species, not just the abiotic parts of the environment (think parts of the environment that are not alive, like soil type, temperature, amount of sunlight, etc.). It’s when cheetahs have to keep getting better at hunting gazelles, while gazelles have to keep getting better at avoiding getting eaten by cheetahs. This is called an “evolutionary arms race,” since the animals are in a loop, one continually developing a better defense (the gazelle) and one continually developing a better offense (the cheetah).
One note before I go further: evolution doesn’t have an end goal. The gazelles aren’t sitting around thinking, “Damn, getting eaten is painful and lethal, how can I avoid it?”; instead, gazelles that are better at not getting eaten (maybe by being faster) are the ones that survive and pass on their genes. It’s natural selection in action.
The Red Queen hypothesis is best explained with a concrete example: say hello to a primo case study, the newt and the garter snake. The newt is actually any species of newt that are in the genus Taricha. They are all armed with tetrodotoxin, or TTX. TTX is a highly potent neurotoxin that is found in a variety of animals, including the pufferfish. It works by blocking sodium channels, which in turn blocks nerve cells from firing. Ingestion of TTX leads to respiratory distress, paralysis, convolutions, cardiovascular collapse, and often death. It only takes 25 milligrams of the stuff to kill an adult human, and there is no antidote.
The newts carry the TTX in their skin, and one newt has enough TTX to kill anywhere from one to twenty adult humans, let alone a single snake. The garter snakes, on the other hand, have responded by developing immunity to TTX. The sodium channels that are affected by the TTX have adapted and changed so that the TTX no longer has the same, lethal effect.
And here’s where the Red Queen hypothesis really gets tested. For the Red Queen to be involved, the garter snakes can’t just have different sodium channels ““ those sodium channels must have come about as a response to the newts. Fortunately, the newts and the garter snakes are found along the western side of North America, but they’re not always found in the same place. In places where there are just garter snakes and no newts, the garter snakes are highly, highly susceptible to the TTX toxin: if a garter snake from one of these newt-free areas gets fed a newt, the TTX does its job and the snake dies. On the flip side, newts that are living in snake-free areas don’t have the same extremely high TTX levels in their skin as those newts that live with garter snakes. It takes both the snakes and the newts together to get that elevation of offense (TTX in newts) and defense (TTX immunity in snakes) ““ that’s the arms race.
But this isn’t the whole story ““ sometimes, the arms race ends. For the rest of the story, tune in next week!