Phylogeny—parasitic nesting to have evolved independently in at least seven lineages of birds.
Host parasite coevolution, where two species coevolve in an antagonistic fashion, has been shown to be a factor in the evolution of avian brood parasitism. There is an arms race of a sort between the host and parasite, where the host might evolve an adaptation to reject eggs that appear alien. However, then the parasite’s eggs could then begin to mimic the host species. It is believed that this process leads increasing specialization between host and parasite, and in the case of brood parasite this appears to no exception as there are some species such as the common cuckoo that are broad generalists and have been observed to lay their eggs in dozens of different hosts, while on the other end of the spectrum there are species that specialize in only a single host.