Based on the observation of the newt in the coffee pot and because newts reveal their orange bellies when threatened, Butch hypothesized that poisonous newts evolved because they were favored by natural selection — since the poison helped defend them against predators. When it comes to natural selection, we tend to think of an organism becoming adapted to its physical surroundings (e.g., the climate, habitat, etc.) — and not necessarily to the organisms around it. For example, the white wintertime coat of the snowshoe hare is an adaptation that helps them blend in to the snowy landscape.
But in reality, both the biotic (living) and abiotic (non-living) environment can trigger evolution. For example, both turtles and snails have evolved hard shells that protect them from ravenous predators (part of the biotic environment). Butch wondered if newts had evolved their toxins in response to part of their biotic environment — in this case, to their predators.
Fighting between predators and prey characterizes some biotic interactions, but not all. In many cases, species have evolved in ways that help each other out. For example, many marine animals such as sea turtles, moray eels, and big fish cooperate with cleaner shrimp and wrasses (small fish). Like tiny marine janitors, the shrimp and wrasses clean the big predators by picking parasites off their mouths and bodies. The “janitors” get a free lunch, and the predators get a spring cleaning. Although the big predators usually eat small shrimp and fish, in this case, they have evolved to recognize these brightly colored helpers and cooperate with them instead.