▁the ▁group ▁was ▁free ▁to ▁have ▁sex , ▁usually ▁upon ▁the ▁man ' s ▁asking ▁the ▁woman , ▁and ▁this ▁was ▁the ▁common ▁practice ▁for ▁many ▁years . ▁The ▁group ▁began ▁to ▁fal ter ▁about ▁ 1 8 7 9 – 1 8 8 1 , ▁eventually ▁dis band ing ▁after ▁No yes ▁fled ▁arrest . ▁Several ▁dozen ▁pairs ▁of ▁One id ans ▁quickly ▁married ▁in ▁traditional ▁fashion . ▁▁ ▁The ▁Ker ista ▁Comm une ▁pract iced ▁group ▁marriage ▁in ▁San ▁Francisco ▁from ▁ 1 9 7 1 ▁to ▁ 1 9 9 1 , ▁calling ▁their ▁version ▁poly f idel ity . ▁ ▁It ▁is ▁difficult ▁to ▁estimate ▁the ▁number ▁of ▁people ▁who ▁actually ▁practice ▁group ▁marriage ▁in ▁modern ▁soci eties , ▁as ▁such ▁a ▁form ▁of ▁marriage ▁is ▁not ▁officially ▁recognized ▁or ▁permitted ▁in ▁any ▁juris diction ▁in ▁the ▁U . S ., ▁and ▁de ▁j ure ▁illegal ▁in ▁many . ▁It ▁is ▁also ▁not ▁always ▁visible ▁when ▁people ▁sharing ▁a ▁residence ▁consider ▁themselves ▁priv ately ▁to ▁be ▁a ▁group ▁marriage . ▁ ▁Port ray al ▁in ▁literature ▁ ▁Group ▁marriage ▁has ▁been ▁a ▁literary ▁theme , ▁particularly ▁in ▁science ▁fiction , ▁and ▁especially ▁in ▁the ▁later ▁nov els ▁of ▁Robert ▁A . ▁Hein lein ▁such ▁as ▁Str anger ▁in ▁a ▁Str ange ▁Land , ▁Friday , ▁Time ▁En ough ▁for ▁Love , ▁and ▁The ▁Moon ▁Is ▁a ▁Har sh ▁M ist ress . ▁ ▁Str anger ▁in ▁a ▁Str ange ▁Land ▁describes ▁a ▁commun al ▁group ▁much ▁like ▁the ▁One