ɪn sˈʌtʃ sˈɪstəmz, ðə kˌɑːmpətˈɪʃən bᵻtwˌiːn hˈoʊst ænd pˈæɹəsˌaɪt ɪz ˈɔfən kˈæɹɪktɚɹˌaɪzd æz ɐn ˌɛvəlˈuːʃənˌɛɹi "ˈɑːɹmz ɹˈeɪs", sˌoʊ ðə mˈoːɹ ɹˈæpɪdli wˈʌn ˈɔːɹɡənˌɪzəm kæn tʃˈeɪndʒ ɪts mˈɛθəd ʌv ɐtˈæk ɔːɹ dᵻfˈɛns, ðə bˈɛɾɚ.
In such systems, the competition between host and parasite is often characterized as an evolutionary "arms race", so the more rapidly one organism can change its method of attack or defense, the better.