In a new study researchers from the University of California-Santa Barbara show that parasitism independently evolved many more times than originally thought. To conduct their analysis, researchers examined how often parasitism evolved from non-parasitic ancestors. They concluded that it evolved at least 223 times, far more than the previous estimate of 60. As shown below, parasitism arose more times in certain phyla (e.g., arthropods, nematodes, flatworms, and mollusks) than in others. Parasitism evolved on at least 143 occasions in the arthropods, 18 times among the nematodes, with Platyhelminthes (flatworms) saw parasitism evolve 13 times. Counterintuitively, the authors’ analysis revealed that parasitism is not an evolutionary dead end, as many biologists suspected. Being a parasite requires a certain level of specialization, which is not always conducive to speciation. However, when compared to their non-parasitic cousins, parasites spawned new species at the same frequency. This also explains why roughly half of all animal species today qualify as parasites. http://acsh.org/news/2016/08/04/parasitism-evolved-at-least-223-times-among-animals/
