Published June 2016

How Does Cooperation Evolve?


How does cooperation evolve?

Usually when we think of natural selection, we think of competition. Survival of the fittest! Competition is fierce in nature, but almost everywhere we look, we also see examples of cooperation.

When two or more different species cooperate to make a living, scientists call it mutualism.

One of the craziest examples of mutualism can be seen in lichen- those crusty things you often find growing on rocks and tree bark.

Lichen is a combination of fungus and algae—two completely unrelated organisms, working together as one. This cooperation is unexpected because many species of fungus eat and kill algae. They have special tentacles called haustoria that pierce the cell walls of their victims, acting like straws to slurp out a meal.

In lichen, however, the fungus uses its large body to collect moisture and vitamins from the environment which it gives to the algae. In return, the algae uses photosynthesis to produce food that the fungus slowly eats, being careful not to injure or take too much from the algae.

In hindsight, it’s easy to see that this relationship gives both creatures a survival advantage, allowing them to thrive in places they could never dream about living on their own, but how do relationships like this first get started? 

If we imagine an environment with plenty of algae to eat, it seems at first glance that natural selection can only favor fungi with mutations that allow them to eat fast and multiply quickly. Slower, gentler fungi will always lose the competition, making it impossible for cooperation to evolve.

By modeling natural selection mathematically however, scientists have discovered many situations that actually promote the evolution of cooperation.

For example, in environments with small patches of slow growing algae, fast eaters will still out-compete slow eaters if they happen to find themselves on a the same patch of food, but once the algae is gone, fast eaters starve.

When slow eaters happen to find patches that fast eaters haven’t yet found, the simple fact that they’re slow gives their food more time to reproduce, sometimes even forming bridges to new fresh patches of algae that nobody else has access to. In this scenario, natural selection actually favors the nice guy.

Survival of the slowest!

If a mutation crops up in a fungus making it so slow at feeding that individual algae can actually grow and reproduce while being eaten, this fungus will never run out of food.

Like a farmer that gets more fruit from her trees by tending to their needs, from this point on, any mutation in the fungus that helps serve the algae, allowing it to grow faster and stronger, will also help the fungus.

So to sum things up, even though natural selection often forces living things into brutal competition, scientists have discovered many situations in which nature favors cooperation. Even transforming savage parasites into gentle, caring hosts.

These relationships develop, not because individuals decide to work together, but because circumstances of the environment naturally select for cooperation.