How does coevolution differ from evolution?
the coevolution is the scenario where two species are evolving together.
Contrary to habitual evolution scenario where the pression of selection link to severale biotic and abiotic factor, the case of coevolution is strongly link and drive by an interaction between two species.
It could be due to an antagoniste relation ( predator / prey , parasite / host and even competition) where to thrive, each side have to develope better way to attack and defend itself. The best individuals are selected true natural selection wich lead to a stronger selective pressure on the other side and it goes on and on.
It is the same for positive relation like mutualism and symbiosis. The individuals that are most efficients collaborators are selected and the bonds grow more efficient along the history of coevolution. (One has to keep in mind that there is no altruism in those behavior and that those positive interaction can lead to parasitisme if one party can overtrow the other one. Those strategies still always aim to improve the fitness of one of the two participants at the time)