What is Co-Evolution?
Let’s start with a real world example: Far back in evolutionary history in the place that would eventually become Oregon, there was a population of garter snakes that preyed on a population of newts. The newts were mildly toxic, so only garter snakes that were tolerant enough to withstand the toxin would survive to pass on their genes.
Over time this led to the snakes evolving greater and greater tolerance to the toxin, which meant that only newts that still produced enough toxin to ward off the increasingly tolerant snakes would survive to reproduce.
Eventually, after roughly 170 million years of evolution, we are left with populations of rough skinned newts that are some of the most toxic animals in the planet. Swallowing one of these newts can kill an adult human within hours, yet the common garter snakes that evolved in the same area are still able to eat them without dying.
(The High Finned Sperm Whale, 2010)
This back and forth of evolutionary pressure is sometimes known as an “evolutionary arms race”, in which each side is trying to one-up the other to get a survival advantage. It’s also a great example of coevolution. Coevolution is a process where two species in close contact exert alternating selection pressure on each other over evolutionary time.
Coevolution can be between predator and prey species, as in this example, but it can also be between species that help one another instead of competing. The relationship between plants and their pollinators is an example of mutualistic (or mutually beneficial) coevolution; the plants benefit from pollination and the pollinators benefit by obtaining pollen and nectar.
While some plants can be pollinated by many different pollinator species, some have specifically coevolved to only be pollinated by one species. For example, there are some plants that will only release their pollen in response to the vibrations from the buzzing frequency of a specific species of bumblebee.
Other examples of mutualistic coevolution include the coevolution between clownfish and anemones or between humans and the beneficial bacteria that live in our guts to help us digest food.
Non-mutualistic coevolution, like the garter snake and newt example, can also occur between a parasite species and its chosen host or between a plant species and the herbivorous animal that eats it. For example, acacia trees grow longer and sharper thorns to avoid being eaten by herbivores, and in response giraffes develop tougher and longer tongues to tolerate and avoid the thorns.
The High Fin Sperm Whale (photographer). (2010). A rough skinned newt [photography]. Retrieved from https://en.wikipedia.org/wiki/Rough-skinned newt#/media/File:Taricha granulosa (Rough-skinned newt).JPG