Coevolution

In biology, coevolution occurs when changes in at least two species' genetic compositions reciprocally affect each other’s evolution.

There is evidence for coevolution at the level of populations and species. Charles Darwin briefly described the concept of coevolution in On the Origin of Species (1859) and developed it in detail in Fertilisation of Orchids (1862). It is likely that viruses and their hosts coevolve in various scenarios.

However, there is little evidence of coevolution driving large-scale changes in Earth's history, since abiotic factors such as mass extinction and expansion into ecospaces seem to guide the shifts in the abundance of major groups. One proposed specific example was the evolution of high-crowned teeth in grazers when grasslands spread through North America - long held up as an example of coevolution. We now know that these events happened independently.

Coevolution can occur at many biological levels: it can be as microscopic as correlated mutations between amino acids in a protein or as macroscopic as covarying traits between different species in an environment. Each party in a coevolutionary relationship exerts selective pressures on the other, thereby affecting each other's evolution. Coevolution of different species includes the evolution of a host species and its parasites (host–parasite coevolution), and examples of mutualism evolving through time. Evolution in response to abiotic factors, such as climate change, is not biological coevolution (since climate is not alive and does not undergo biological evolution).