▁cross - c ousin " ▁and ▁" bro ther - in - law " ▁are ▁the ▁same , ▁as ▁are ▁the ▁terms ▁for ▁" f em ale ▁cross - c ousin " ▁and ▁" s ister - in - law ". ▁ ▁The ▁remaining ▁types ▁of ▁kin ship ▁termin ology ▁( the ▁" H aw ai ian ", ▁" E sk imo " ▁and ▁" S ud an ese ") ▁do ▁not ▁group ▁parallel ▁c ous ins ▁together ▁in ▁opposition ▁to ▁cross - c ous ins . ▁ ▁Tab o os ▁▁ ▁John ▁May n ard ▁Smith , ▁in ▁The ▁E volution ▁of ▁Sex   ( 1 9 7 8 ) ▁notes ▁that ▁Richard ▁D . ▁Alexander ▁suggested ▁that ▁uncertainty ▁regarding ▁pat ern ity ▁may ▁help ▁account ▁for ▁the ▁inter mar riage ▁tab oo ▁on ▁parallel , ▁but ▁not ▁on ▁cross - c ous ins . ▁F athers ▁who ▁are ▁also ▁brothers ▁may ▁over t ly ▁or ▁cover t ly ▁share ▁sexual ▁relations ▁with ▁the ▁wife ▁of ▁one ▁or ▁the ▁other , ▁raising ▁the ▁possibility ▁that ▁apparent ▁parallel ▁c ous ins ▁are ▁in ▁fact ▁half - s ib lings , ▁s ired ▁by ▁the ▁same ▁father . ▁Like wise , ▁moth ers ▁who ▁are ▁also ▁sister s ▁may ▁over t ly ▁or ▁cover t ly ▁share ▁sexual ▁access ▁to ▁the ▁husband ▁of ▁one ▁or ▁the ▁other , ▁raising ▁the ▁possibility ▁that ▁apparent ▁parallel ▁c ous ins ▁are ▁in ▁fact ▁half - s ib lings , ▁s ired ▁by ▁the ▁same ▁father . ▁Note