Interactions between species are as diverse as they are pervasive. The result is a continual process of adaptation and counteradaptation, where each species evolves continually to keep abreast of interacting species. ~ American evolutionary biologists Sarah Otto & Scott Nuismer
All organisms live in a web of relationships, from synergistic to antagonistic. Interdependencies evolve that range from mutualistic to parasitic.
Species can coevolve with more than one other species. Legumes have simultaneously evolved sophisticated coevolutionary relationships with their rhizobia and with their pollinators. Many parasites evolve adaptations to multiple hosts by partitioning their interactions into different life history stages. ~ John Thompson
Coevolution is adaptive intertwining among species that is inspired by their interaction. Biological self-interest drives the gyre of coevolution.
Coevolutionary arms races are a powerful force driving evolution, adaptation, and diversification. They can generate phenotypic polymorphisms that render it harder for a coevolving parasite or predator to exploit any one individual of a given species. ~ South African zoologist Claire Spottiswoode & Martin Stevens
African cuckoo finches lay their eggs into the nests of tawny-flanked prinias. Female prinias try to weed the fakes out. This can be perplexing, as parasitic eggs are strikingly selfsame. Egged on by parasitism, prinias epigenetically develop new shell hues to catch the cuckoos out. The cuckoo finches retaliate with new fakes. This adaptive cycling takes place within a few breeding seasons. Evolution moves at requisite pace.