XIX.1.3 Host to parasite selection pressure is stronger and more systematic than vice versa

Another reason why the speed of evolution of a parasitic species is generally greater than the speed of evolution of its host lies in the more intense and systematic active selection pressure to which the population of parasites is exposed compared to the population of its hosts.While, in each generation, only part of the host individuals are exposed to the action of the parasite, every individual of the parasitic species in every generation must interact with a host organism (Dawkins 1982).Thus, parasites are constantly exposed to selection pressure from the host, while the hosts are exposed to selection pressure from parasitesonly unsystematically and occasionally.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.