orph ological ▁st asis ". ▁For ▁example , ▁the ▁Amazon ian ▁f rog ▁Pr ist im ant is ▁o ck enden i ▁is ▁actually ▁at ▁least ▁three ▁different ▁species ▁that ▁diver ged ▁over ▁ 5 ▁million ▁years ▁ago . ▁ ▁St abil izing ▁selection ▁has ▁been ▁invoked ▁as ▁a ▁force ▁maintain ing ▁similarity ▁in ▁species ▁complex es , ▁especially ▁they ▁adapt at ▁to ▁special ▁environments , ▁such ▁as ▁a ▁host ▁in ▁the ▁case ▁of ▁sym b ion ts ▁or ▁extreme ▁environments , ▁const ra ins ▁possible ▁directions ▁of ▁evolution : ▁in ▁such ▁cases , ▁strongly ▁diver gent ▁selection ▁is ▁not ▁to ▁be ▁expected . ▁Also , ▁a sex ual ▁reprodu ction , ▁such ▁as ▁through ▁ap om ix is ▁in ▁plants , ▁may ▁separate ▁line ages ▁without ▁producing ▁a ▁great ▁degree ▁of ▁morph ological ▁different iation . ▁ ▁A ▁species ▁complex ▁is ▁usually ▁a ▁group ▁that ▁has ▁one ▁common ▁ancest or ▁( a ▁mon oph y let ic ▁group ), ▁but ▁closer ▁exam ination ▁can ▁sometimes ▁dis pro ve ▁that . ▁For ▁example , ▁yellow - sp otted ▁" fire ▁sal am and ers " ▁in ▁the ▁genus ▁Sal am andra , ▁formerly ▁all ▁class ified ▁as ▁one ▁species ▁S . ▁sal am andra , ▁are ▁not ▁mon oph y let ic : ▁the ▁C ors ican ▁fire ▁sal am ander ' s ▁closest ▁relative ▁has ▁been ▁shown ▁to ▁be ▁the ▁entirely - black ▁Al pine ▁sal am ander . ▁In ▁such ▁cases , ▁similarity ▁has ▁ar isen ▁from ▁conver gent ▁evolution .