Coevolution favoring mutualism Parasitism

the gram-negative bacterium wolbachia within insect cell

long-term coevolution leads relatively stable relationship tending commensalism or mutualism, as, else being equal, in evolutionary interest of parasite host thrives. parasite may evolve become less harmful host or host may evolve cope unavoidable presence of parasite—to point parasite s absence causes host harm. example, although animals infected parasitic worms harmed, , therefore parasitized, such infections may reduce prevalence , effects of autoimmune disorders in animal hosts, including humans. in more extreme example, nematode worms cannot reproduce, or survive, without infection wolbachia bacteria.

lynn margulis , others have argued, following peter kropotkin s 1902 mutual aid: factor of evolution, natural selection drives relationships parasitism mutualism when resources limited. process may have been involved in symbiogenesis formed eukaryotes intracellular relationship between archaea , bacteria, though sequence of events remains largely undefined.