In bird reproduction, parasitism and cooperation coevolve

Science “How Cooperation Defeats Cheats”

Science “Brood Parasitism and the Evolution of Cooperative Breeding in Birds”

Live Science “How Birds Cooperate to Defeat Cuckoos”

It is fascinating that being a cooperative breeder is both attractive to parasites (because they can achieve better reproductive success by successfully parasitizing the nest of cooperative breeders) and the best way to repel brood parasites. The success of cooperation makes it a bigger target for parasites, whose attempts to exploit lead to even tighter cooperation. So it is not entirely accurate to say that the threat of parasitism leads to cooperation, as this is truly coevolution.

I would suggest that this might be a bigger theme in evolution: that the opportunity for parasitism arises when cooperation fosters biological success and therefore a viable potential host. Clearly the biggest cooperative venture in evolution — the transition from unicellularity to multicellularity — opened up a myriad of opportunities for parasites, whose threat also tightly fine-tuned the cooperation of those multiple cells.