How does evolution explain mutual symbiosis?

Mutual symbiosis (or just symbiosis, as it's usually called), is a HUGE factor in evolution. Before multi-cellular organisms developed, the boundaries between individual organisms were blurred. Bacteria often exchanged genetic material. read more

I believe there are parasites that release chemicals that influence the behaviour of their host but they are parasites and not necessarily simbiotic; Simbiosis implies a mutual benefit between the two, whereas parasitical organisms purpose is for their own gain. read more

As to the question of what evolution has to say about symbiosis, the general observation is that a long period of mutual co-evolution is required in some cases to form the symbiotic relationship. Some scientists claim that such co-evolution is a major force in shaping the natural world. read more