▁sex ▁to ▁promote ▁group ▁coh es ion ▁in ▁social ▁animals . ▁C ement ing ▁social ▁bond age ▁is ▁one ▁of ▁the ▁most ▁prominent ▁the or ized ▁select ive ▁advantages ▁of ▁group ▁selection ▁theory . ▁Exper ts ▁in ▁the ▁evolution ▁of ▁sex ▁such ▁as ▁John ▁May n ard ▁Smith ▁advoc ate ▁for ▁the ▁idea ▁that ▁the ▁exchange ▁of ▁sexual ▁fav ors ▁helps ▁con ge al ▁and ▁local ize ▁the ▁ass ort ment ▁of ▁alle les ▁in ▁isolated ▁population ▁and ▁therefore ▁is ▁potentially ▁a ▁very ▁strong ▁force ▁in ▁evolution . ▁May n ard ▁Smith ▁has ▁also ▁written ▁extens ively ▁on ▁the ▁" sem inal ▁fluid ▁sw apping ▁theory " ▁log istic ▁application ▁of ▁the ▁ass ort ment ▁of ▁alle les ▁as ▁a ▁more ▁accurate ▁synth etic ▁dep iction ▁of ▁the ▁Hard y – We in berg ▁principle ▁in ▁cases ▁of ▁sever ely ▁inter bre eding ▁populations . ▁ ▁E volution ary ▁models ▁The ▁effect ▁of ▁sexual ▁response ▁is ▁thought ▁to ▁be ▁a ▁pl astic ▁positive ▁rein for cement ▁behavior ▁mod ifier ▁associated ▁with ▁the ▁Bald win ▁effect . ▁The ▁display ▁of ▁secondary ▁sex ▁characteristics ▁in ▁humans ▁such ▁as ▁a ▁pen is - like ▁en larg ed ▁cl itor is ▁in ▁females ▁during ▁ar ous al ▁and ▁gy ne com ast ia ▁in ▁males ▁are ▁thought ▁to ▁have ▁once ▁been ▁objects ▁of ▁mate ▁selection ▁in ▁human ▁evolution ▁because ▁of ▁the ▁pers istence ▁of ▁the ▁phenomen on ▁of ▁these ▁features ▁inv oking ▁sexual ▁ar ous al ▁for ▁potential ▁m ates ▁in ▁cross - c ult ural ▁studies