African Fossil Record Contributions African Fossil Record

African Fossil Record Contributions

African Fossil Record

African Fossil Record Contributions to the 'Out of Africa' Theory

The African fossil record represents the foundation upon which modern archeologists base many of their theories concerning the evolutionary history of modern humans (Klein, 2008). When combined with DNA sequencing, the African fossil record shows that modern humans probably emerged about 200-150 ka (thousand years ago) and expanded into Eurasia as recently as 50 ka. This 'Out of Africa' theory would therefore not exist without the African fossil record.

The human fossil record reveals that humans split into three morphologically distinct species approximately 500,000 years ago; Homo sapiens, H. neanderthalensis, and H. erectus, in Africa, Europe, and Asia, respectively (Klein, 2008). The African fossil record contains no evidence that Neanderthals were ever in Africa, therefore it is assumed that modern humans emerged in Africa in the absence of a Neanderthal contribution (Klein, 2011). The emergence of modern morphological features is estimated to have occurred in Africa between 250-50 ka. If the evolutionary clock is rolled back still further, H. heidelbergensis probably represents the common ancestor for the H. sapiens and H. neanderthalensis. H. heidelbergensis fossils date to 600-400 ka and this species is suspected of having carried artifacts out of Africa to Europe around 600 ka and of being the only hominin species in existence at the time.

While the African fossil record has provided an intriguing insight into human evolution, in the absence of independent confirmation, its validity was suspect. This changed when two decades ago biologists began sequencing mitochondrial DNA from both modern humans and hominid fossils (Klein, 2008). The results of these studies, which are still ongoing, are that they largely agree with the fossil record. The combination of these two lines of evidence has given archeologists increased confidence in the fossil record for both Neanderthals and H. sapiens fossils found in Africa. The validity of the African fossil record has thus been increased substantially.

The most controversial issues about the fossil record remaining is whether Neanderthals and H. sapiens interacted and interbred at any point in their history (Klein, 2008). So far, both the fossil and DNA evidence suggests this rarely happened and any interbreeding events were so rare that Neanderthal DNA was extinguished before making a detectable contribution to the modern human gene pool.

There is also substantial controversy over when modern behavioral traits emerged. Klein (2008) adheres to the theory that behavioral traits continued to evolve long after H. Sapiens had appeared in Africa 200 ka. This theory is based on the emergence of unique morphological traits in the skulls of H. sapiens during the past 200 ka, thereby correlating skull features with behavioral sophistication. Klein further explains that the absence of Neanderthal DNA in modern humans is probably due to a wide behavioral gap between the two species.