4,5 milyar y\u0131ll\u0131k d\u00fcnya tarihinde, g\u00f6reli olarak ge\u00e7 sahneye \u00e7\u0131kan insanl\u0131k, ba\u015frol\u00fc kapm\u0131\u015f durumda. Son iki y\u00fcz y\u0131ld\u0131r roller de\u011fi\u015fmi\u015f gibi g\u00f6z\u00fckse de, iklim belki de insan evrimindeki ba\u015f akt\u00f6rd\u00fc.<\/p>\n
Atalar\u0131m\u0131za ait en eski fosil kan\u0131tlar\u0131n b\u00fcy\u00fck bir k\u0131sm\u0131 Afrika\u2019dan geldi\u011fi i\u00e7in, antropologlar\u0131n \u00e7o\u011fu insanlar\u0131n Afrika\u2019da evrimle\u015fti\u011fi konusunda hemfikir. Afrika\u2019daki fosillerin \u00e7o\u011fu ise Kuzeydo\u011fu\u2019da Kenya ve Etiyopya ba\u015fta olmak \u00fczere, Do\u011fu ve G\u00fcney Afrika\u2019da bulunmu\u015ftur. Bu b\u00f6lgede milyonlarca y\u0131ld\u0131r faal olan volkanizma sayesinde, fosillerin bulundu\u011fu katmanlar, ya\u015flar\u0131 radyometrik y\u00f6ntemlerle olduk\u00e7a do\u011fru olarak \u00f6l\u00e7\u00fclebilen volkanik kaya\u00e7larla adeta b\u00f6lmelere ayr\u0131lm\u0131\u015ft\u0131r. B\u00f6ylelikle g\u00fcn y\u00fcz\u00fcne \u00e7\u0131kar\u0131lan fosilleri, ait olduklar\u0131 katmanlara, dolay\u0131s\u0131yla ait olduklar\u0131 d\u00f6nemlere g\u00f6re s\u0131ralayarak insan evrimini anlamaya \u00e7al\u0131\u015fmak m\u00fcmk\u00fcn.<\/p>\n
\u0130nsan evrimini a\u00e7\u0131klamak i\u00e7in pek \u00e7ok hipotez ortaya at\u0131lm\u0131\u015ft\u0131r. Bu hipotezlerden baz\u0131lar\u0131 uzun y\u0131llar boyunca korumaya muhta\u00e7 yavrular\u0131n korunmas\u0131 ve beslenmesi i\u00e7in geli\u015ftirilen stratejiler gibi sosyal etmenlere odaklan\u0131rken, baz\u0131lar\u0131 da yiyecek toplama, savunma, avlanma amac\u0131yla alet kullan\u0131m\u0131 gibi yeni teknolojilere odaklan\u0131yor. Son zamanlarda geli\u015fmekte olan iklimsel hipotezler ise, Afrika\u2019n\u0131n floras\u0131 ve atalar\u0131m\u0131z\u0131n da dahil oldu\u011fu faunas\u0131n\u0131n iklimsel de\u011fi\u015fimler taraf\u0131ndan \u015fekillendirilmi\u015f olabilece\u011fini \u00f6ne s\u00fcr\u00fcyor.<\/p>\n
\u0130klim de\u011fi\u015fiminin insan evrimini \u015fekillendirip \u015fekillendirmedi\u011fi sorusu Darwin\u2019in T\u00fcrlerin K\u00f6keni<\/em>\u2019nden beri sorulan bir soru olsa da ancak son 20-30 y\u0131ld\u0131r, artan insans\u0131 fosili say\u0131s\u0131 ve geli\u015fen paleoiklim (ge\u00e7mi\u015f iklim) \u00e7al\u0131\u015fmalar\u0131 sayesinde yan\u0131tlar \u00fcretilmeye ba\u015fland\u0131. \u0130klimsel insan evrimi hipotezlerine g\u00f6re, iklimdeki de\u011fi\u015fimler ekolojik yap\u0131y\u0131 de\u011fi\u015ftirerek se\u00e7ilim bask\u0131lar\u0131 yarat\u0131yor. Ger\u00e7ekten de, d\u00fcnya tarihindeki en b\u00fcy\u00fck \u00e7apl\u0131 iklim de\u011fi\u015fikliklerine y\u00fcksek h\u0131zda yok olma, t\u00fcrle\u015fme ve uyarlanma olaylar\u0131n\u0131n e\u015flik etti\u011fi g\u00f6r\u00fcl\u00fcyor. \u00d6rne\u011fin, 34 milyon y\u0131l \u00f6nce g\u00f6rece h\u0131zl\u0131 bir \u015fekilde so\u011fuyan iklim ve Antarktika\u2019ya ula\u015fan buzullar sonras\u0131nda yeni ortamlara uyum sa\u011flayan pek \u00e7ok taksonun ortaya \u00e7\u0131kt\u0131\u011f\u0131 fosil kay\u0131tlar\u0131ndan anla\u015f\u0131labiliyor. Benzer \u015fekilde atalar\u0131m\u0131zda g\u00f6r\u00fclen yok olu\u015f, t\u00fcrle\u015fme ve davran\u0131\u015fsal de\u011fi\u015fimlerin ge\u00e7mi\u015f Afrika iklimindeki de\u011fi\u015fimlerle ili\u015fkili olmas\u0131 m\u00fcmk\u00fcn.<\/p>\n \u0130lk insans\u0131lar\u0131n ortaya \u00e7\u0131k\u0131\u015flar\u0131 ve yok olu\u015flar\u0131, bipedalism (iki ayak \u00fczerinde y\u00fcr\u00fcme), di\u015f yap\u0131s\u0131n\u0131n farkl\u0131la\u015fmas\u0131, alet kullan\u0131m\u0131, beynin b\u00fcy\u00fcmesi ve Afrika d\u0131\u015f\u0131na g\u00f6\u00e7 gibi \u00f6nemli evrimsel olaylar, ekolojik yap\u0131n\u0131n de\u011fi\u015fmesi, yani dolayl\u0131 olarak iklim de\u011fi\u015fimiyle ili\u015fkilendiriliyor. Ancak \u00e7e\u015fitli nedenlerle, herhangi bir d\u00f6neme ait bulunan insans\u0131 fosillerinin say\u0131s\u0131 ve \u00e7e\u015fitlili\u011fi di\u011fer taksonlara oranla daha az oldu\u011fundan, paleontolojistler (fosil bilimciler) atalar\u0131m\u0131za ayn\u0131 ekosistemde e\u015flik etmi\u015f olan bovidae, yani antilop, ceylan, ke\u00e7i gibi boynuzlugillerin fosillerinden, iklimin etkilerine dair ipu\u00e7lar\u0131 toplamaya \u00e7al\u0131\u015f\u0131yorlar. Bu gevi\u015f getiren memeli topluluklar\u0131 Afrika fosillerinin \u00fc\u00e7te birini olu\u015ftururken, insans\u0131 fosilleri y\u00fczde 1\u2019inden az bir k\u0131sm\u0131n\u0131 te\u015fkil ediyor. Son 6 milyon y\u0131l\u0131n bovidae fosillerine bak\u0131ld\u0131\u011f\u0131nda, normal seyrine g\u00f6re daha h\u0131zl\u0131 ger\u00e7ekle\u015fen t\u00fcrle\u015fme ve yok olu\u015f d\u00f6nemlerinin oldu\u011fu g\u00f6r\u00fcl\u00fcyor.<\/p>\n Afrika\u2019n\u0131n ge\u00e7mi\u015f iklim de\u011fi\u015fikliklerine iki farkl\u0131 zaman \u00f6l\u00e7e\u011finden bakmak m\u00fcmk\u00fcn. Jeolojik zaman \u00f6l\u00e7e\u011finde, yani milyon y\u0131llar olarak bak\u0131ld\u0131\u011f\u0131nda, Afrika\u2019n\u0131n son 5 milyon y\u0131ld\u0131r devam etmekte olan bir kurakla\u015fma s\u00fcrecinde oldu\u011fu g\u00f6r\u00fcl\u00fcyor. Buna ba\u011fl\u0131 olarak de\u011fi\u015fen bitki \u00f6rt\u00fcs\u00fc ve di\u011fer kaynaklar\u0131n, ortamdaki canl\u0131lar\u0131n evrimsel de\u011fi\u015fimlerini etkilemi\u015f olmas\u0131 bekleniyor. Toprakta bulunan karbon miktarlar\u0131, fosil polen ve bitki \u00e7al\u0131\u015fmalar\u0131 ve di\u011fer paleoiklim kay\u0131tlar\u0131 (\u00f6rne\u011fin, okyanus taban\u0131ndan elde edilen sahra tozu kay\u0131tlar\u0131); Afrika\u2019da gittik\u00e7e seyrelen ve yap\u0131sal olarak da de\u011fi\u015fen bir bitki \u00f6rt\u00fcs\u00fcne i\u015faret ediyor.<\/p>\n Ancak daha y\u00fcksek \u00e7\u00f6z\u00fcn\u00fcrl\u00fckte, yani onbin-y\u00fczbin y\u0131llar aras\u0131ndaki orbital zaman \u00f6l\u00e7e\u011finde bak\u0131ld\u0131\u011f\u0131nda, bu genel kurakla\u015fma s\u00fcrecinin i\u00e7inde pek \u00e7ok, kurak-ya\u011f\u0131\u015fl\u0131-kurak-ya\u011f\u0131\u015fl\u0131 d\u00f6ng\u00fclerin ger\u00e7ekle\u015fti\u011fi g\u00f6r\u00fcl\u00fcyor. Farkl\u0131 paleoiklim kay\u0131tlar\u0131n\u0131n (\u00f6rne\u011fin, mevcut g\u00f6llerin ya da eskiden g\u00f6l olan b\u00f6lgelerdeki katmanlardan elde edilen kay\u0131tlar\u0131n) de\u011ferlendirmeye al\u0131nmas\u0131 ve \u00f6nceki verilerin yeniden analizleriyle in\u015fa edilen kurak-ya\u011f\u0131\u015fl\u0131 d\u00f6ng\u00fcler gittik\u00e7e belirginle\u015fiyor. Yeni bulgular Afrika insans\u0131lar\u0131n\u0131n, b\u00f6lgesel muson de\u011fi\u015fimlerinin kontrol\u00fcndeki bir iklimde evrimle\u015ftiklerini s\u00f6yl\u00fcyor. G\u00f6zlemlerin, paleoiklim kay\u0131tlar\u0131n\u0131n ve fosil say\u0131s\u0131n\u0131n art\u0131r\u0131lmas\u0131 ile iklim hipotezlerinin test edilmesi m\u00fcmk\u00fcn olabilecek.<\/p>\n <\/p>\n Kaynaklar<\/strong><\/p>\n 1) W. Ruddiman, Earth\u2019s Climate: Past and Future<\/em>, 2000.<\/p>\n 2) W. Ruddiman, EOS Vol. 89 No.18, Nisan 2008.<\/p>\n 3) P. deMenocal, Climate and Human Evolution, Science<\/em>, Vol. 331 No. 6017, 2011.<\/p>\n 4) M. Trauth, et al.,<\/em> Human evolution in a variable environment: the amplifier lakes of Eastern Africa, Quaternary Science Reviews<\/em>, Vol. 29 2010.<\/p>\n","protected":false},"excerpt":{"rendered":" 4,5 milyar y\u0131ll\u0131k d\u00fcnya tarihinde, g\u00f6reli olarak ge\u00e7 sahneye \u00e7\u0131kan insanl\u0131k, ba\u015frol\u00fc kapm\u0131\u015f durumda. Son iki y\u00fcz y\u0131ld\u0131r roller de\u011fi\u015fmi\u015f gibi g\u00f6z\u00fckse de, iklim belki de insan evrimindeki ba\u015f akt\u00f6rd\u00fc. Atalar\u0131m\u0131za ait en eski fosil kan\u0131tlar\u0131n b\u00fcy\u00fck bir k\u0131sm\u0131 Afrika\u2019dan geldi\u011fi i\u00e7in, antropologlar\u0131n \u00e7o\u011fu insanlar\u0131n Afrika\u2019da evrimle\u015fti\u011fi konusunda hemfikir. Afrika\u2019daki fosillerin \u00e7o\u011fu ise Kuzeydo\u011fu\u2019da Kenya […]<\/p>\n","protected":false},"author":800,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[122,19],"tags":[200,308,230],"class_list":["post-9799","post","type-post","status-publish","format-standard","hentry","category-85-sayi","category-bilim-gundemi","tag-evrim","tag-iklim","tag-insanlik-tarihi"],"acf":[],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t