▁observed ▁in ▁Sp ong es , ▁the ▁most ▁primitive ▁group ▁in ▁the ▁animal ▁kingdom . ▁ ▁Sp ong es ▁develop ▁through ▁the ▁aggreg ation ▁of ▁individual ▁cells ▁into ▁larger ▁clusters . ▁ ▁Through ▁memb rane - binding ▁prote ins ▁and ▁secret ed ▁ ions , ▁individual ▁sp on ge ▁cells ▁are ▁able ▁to ▁coordinate ▁aggreg ation ▁while ▁prevent ing ▁fusion ▁between ▁different ▁species ▁or ▁even ▁different ▁individuals . ▁ ▁This ▁was ▁discovered ▁when ▁attempts ▁to ▁gra ft ▁sp on ge ▁cells ▁from ▁different ▁species ▁or ▁individuals ▁of ▁the ▁same ▁species ▁failed , ▁while ▁attempts ▁using ▁cells ▁from ▁the ▁same ▁individual ▁merged ▁successfully . ▁ ▁This ▁is ▁likely ▁due ▁to ▁distinct ▁cad her ins , ▁a ▁calci um - binding ▁memb rane ▁protein , ▁expressed ▁by ▁different ▁sp on ge ▁species ▁and ▁individuals . ▁ ▁Cad her ins ▁are ▁present ▁in ▁more ▁complex ▁organ isms ▁as ▁well . ▁ ▁In ▁mouse ▁emb ry os , ▁E - c ad her in ▁on ▁cell ▁memb ran es ▁is ▁responsible ▁for ▁the ▁ad hes ion ▁of ▁cells ▁needed ▁for ▁emb ry onic ▁comp action . ▁ ▁Cell ▁recognition ▁for ▁injury ▁response ▁ ▁When ▁a ▁large ▁multi - cell ular ▁organ ism ▁sust ains ▁an ▁injury , ▁cell - cell ▁recognition ▁is ▁often ▁involved ▁in ▁bringing ▁certain ▁types ▁of ▁cells ▁to ▁the ▁site ▁of ▁an ▁injury . ▁ ▁A ▁common ▁example ▁of ▁this ▁is ▁select in - express ing ▁cells ▁in ▁animals . ▁ ▁Select in ▁is ▁a ▁re ceptor ▁protein ▁found ▁on ▁the ▁memb ran es