▁effect ▁on ▁function ▁than ▁non - con serv ative ▁rep lac ements . ▁The ▁reduced ▁effect ▁of ▁conserv ative ▁rep lac ements ▁on ▁function ▁can ▁also ▁be ▁seen ▁in ▁the ▁occurrence ▁of ▁different ▁rep lac ements ▁in ▁nature . ▁Non - con serv ative ▁rep lac ements ▁between ▁prote ins ▁are ▁far ▁more ▁likely ▁to ▁be ▁removed ▁by ▁natural ▁selection ▁due ▁to ▁their ▁de le ter ious ▁effects . ▁ ▁See ▁also ▁▁▁ ▁Seg reg ating ▁site ▁ ▁Ult ra - con ser ved ▁element ▁ ▁Se quence ▁alignment ▁ ▁Se quence ▁alignment ▁software ▁ ▁References ▁▁ ▁Category : B io chem istry ▁Category : A min o ▁ac ids <0x0A> </s> ▁David ▁Low ▁H ack ett ▁( Nov ember ▁ 1 2 , ▁ 1 9 2 6 ▁– ▁April ▁ 2 3 , ▁ 2 0 1 1 ) ▁was ▁an ▁American ▁official . ▁ ▁Born ▁in ▁D ed ham , ▁Massachusetts , ▁H ack ett ▁was ▁appointed ▁by ▁President ▁John ▁F . ▁Kennedy ▁to ▁head ▁the ▁President ' s ▁Committee ▁on ▁Ju ven ile ▁Del in quency ▁and ▁Youth ▁Crime . ▁Later , ▁H ack ett ▁head ed ▁a ▁study ▁group ▁for ▁the ▁establishment ▁of ▁a ▁domestic ▁peace ▁corps ▁group ▁which ▁later ▁became ▁Amer i Cor ps ▁V ista . ▁A ▁friend ▁of ▁Robert ▁F . ▁Kennedy , ▁H ack ett ▁helped ▁with ▁Kennedy ' s ▁president ial ▁campaign ▁in ▁ 1 9 6 8 . ▁He ▁served ▁in ▁the ▁United ▁States ▁Army ▁in ▁Europe ▁during ▁World ▁War ▁II ▁and