Coevolution

“Two lineages can each become part of the environment pushing the other to change.”

01 / PLAINLY

What it means, plainly

Coevolution occurs when evolutionary change in one species creates reciprocal selection on another, and vice versa.

02 / CONTEXT

A little more

Coevolution requires reciprocal evolutionary change, not mere coexistence. It may involve species pairs or entire networks and can produce cooperation, arms races, or different outcomes across regions.

03 / WHY IT MATTERS

Why it matters

It helps explain why defenses and attacks, flowers and pollinators, or hosts and parasites change in response to one another.

04 / EXAMPLE

A familiar example

A plant evolves a toxin; some herbivores evolve tolerance, which may then favor a different set of plant defenses.

05 / LIMIT

What it does not mean

Interaction does not prove coevolution: evidence must show that each species imposes selection on the other.

06 / NOTICE

Notice it in your day

Choose an ecological pair and draw two causal arrows. For each arrow, write what observation demonstrates actual selection.

FINAL NOTE

The idea worth keeping

Look for evolutionary reciprocity and rule out cases where only one species responds to a shared environment.

QUESTIONS / 02

Questions people still have

Does coevolution always benefit both species?

No. It includes mutualisms but also conflicts between predators and prey, parasites and hosts, or competitors.

Can coevolution differ between places?

Yes. Species, pressures, and outcomes can form a geographic mosaic rather than one uniform arms race.