▁advance ▁that ▁allowed ▁forest ▁clear ance ▁on ▁a ▁large ▁scale ▁to ▁create ▁far ms . ▁This ▁use ▁of ▁pol ished ▁stone ▁axes ▁increased ▁greatly ▁in ▁the ▁Ne ol ith ic , ▁but ▁were ▁originally ▁used ▁in ▁the ▁preceding ▁Mes ol ith ic ▁in ▁some ▁areas ▁such ▁as ▁Ireland . ▁Agricult ure ▁fed ▁larger ▁populations , ▁and ▁the ▁transition ▁to ▁sed ent ism ▁allowed ▁simultaneously ▁raising ▁more ▁children , ▁as ▁inf ants ▁no ▁longer ▁needed ▁to ▁be ▁carried , ▁as ▁nom adic ▁ones ▁must . ▁Additionally , ▁children ▁could ▁contribute ▁labor ▁to ▁the ▁raising ▁of ▁cro ps ▁more ▁readily ▁than ▁they ▁could ▁to ▁the ▁h unter - g ather er ▁economy . ▁ ▁With ▁this ▁increase ▁in ▁population ▁and ▁avail ability ▁of ▁labor ▁came ▁an ▁increase ▁in ▁labor ▁special ization . ▁What ▁triggered ▁the ▁pro gression ▁from ▁early ▁Ne ol ith ic ▁villages ▁to ▁the ▁first ▁cities , ▁such ▁as ▁U ru k , ▁and ▁the ▁first ▁civil izations , ▁such ▁as ▁S umer , ▁is ▁not ▁specifically ▁known ; ▁however , ▁the ▁emer gence ▁of ▁increasing ly ▁hier arch ical ▁social ▁structures ▁and ▁special ized ▁labor , ▁of ▁trade ▁and ▁war ▁amongst ▁adjacent ▁cult ures , ▁and ▁the ▁need ▁for ▁collect ive ▁action ▁to ▁overcome ▁environmental ▁challeng es ▁such ▁as ▁ir rig ation , ▁are ▁all ▁thought ▁to ▁have ▁played ▁a ▁role . ▁ ▁Metal ▁tools ▁Cont inu ing ▁improvements ▁led ▁to ▁the ▁furn ace ▁and ▁bell ows ▁and ▁provided , ▁for ▁the ▁first ▁time , ▁the ▁ability ▁to ▁sm elt ▁and ▁for