Evolution of a parasite
A parasite plays the role of an attacker in the evolutionary battle between a parasite and its host. This gives it a certain advantage – it can “choose the weapon”. Its second advantage is generally provided by its life strategy and its biodemographic (life history) parameters. Parasites leave provision of a major part of vegetative functions to their host organisms, so that they can invest a large portion of their resources into the production of progeny. Consequently, very many of them produce a great many progeny during their lifetimes (Combes 2001). For example, the hookworm (Necator) produces 15,000 eggs per day, some nematode worms (Ascaris) produce 200,000 and tapeworms produce (Taenia saginata) 720,000. This fact can have a fundamental impact on the progress and result of the evolutionary battle between the parasite and the host. If a species produces a great many progeny, of which only a small portion survive to reproductive age, then natural selection can act very effectively and evolution of adaptive traits can occur extremely rapidly. In addition, the fact that the generation period of a parasite is generally many time shorter than that of the host contributes to the fact that the evolution of a parasite occurs much faster than the evolution of its host.