▁Other ▁generation ▁schemes ▁were ▁made ▁through ▁random ▁selection ▁in ▁a ▁determin istic ▁fashion , ▁followed ▁by ▁tun ing ▁to ▁create ▁a ▁real istic ▁result . ▁Cre atures ▁were ▁often ▁generated ▁by ▁mixing ▁and ▁matching ▁random ▁parts ▁from ▁a ▁library , ▁and ▁then ▁adjust ing ▁the ▁underlying ▁ske leton ▁so ▁that ▁the ▁creature ▁appeared ▁real istic ; ▁a ▁creature ▁with ▁a ▁tiny ▁body ▁could ▁not ▁support ▁a ▁giant ▁head , ▁for ▁example . ▁To ▁create ▁behaviour ▁for ▁the ▁cre atures ▁generated ▁by ▁the ▁proced ural ▁generation ▁system , ▁the ▁system ▁tags ▁objects ▁that ▁it ▁creates , ▁and ▁then ▁assign s ▁cre atures ▁various ▁aff inity ▁levels ▁based ▁on ▁these ▁tags ; ▁cre atures ▁are ▁then ▁driven ▁to ▁find ▁objects ▁they ▁like ▁and ▁avoid ▁those ▁they ▁dis like , ▁and ▁allows ▁the ▁artificial ▁intelligence ▁aspects ▁of ▁cre atures ▁to ▁communicate ▁directly ▁to ▁coordinate ▁their ▁respective ▁movements . ▁Dun can ▁describes ▁this ▁as ▁generating ▁complex ▁patterns ▁on ▁relatively ▁simple ▁rules ▁that ▁create ▁surprising ▁results ; ▁he ▁describes ▁being ▁surprised ▁when , ▁after ▁hunting ▁av ian ▁cre atures ▁over ▁a ▁body ▁of ▁water ▁to ▁have ▁one ▁of ▁the ▁k ills ▁e aten ▁by ▁the ▁sudden ▁appearance ▁of ▁a ▁sh ark - like ▁creature . ▁ ▁The ▁generation ▁system ▁can ▁create ▁a ▁variety ▁of ▁planet ▁e cos ystem s , ▁including ▁differ ing ▁rot ational ▁periods , ▁the ▁end - effect s ▁of ▁natural ▁er os ion , ▁and ▁behaviour al ▁cycles ▁for ▁the ▁cre atures . ▁The ▁amount ▁of ▁life ▁on ▁plan ets ▁are ▁fact ored ▁based