There has long been a debate surrounding how our earliest ancestors came to be and how they eventually evolved into humans as we know them today. Although we do not know the exact answer, scientists now subscribe to one of two major theories. These two theories are referred to as the Out-of-Africa Theory and the Multiregional Theory.
The Out-of-Africa Theory and the Multiregional Theory actually have one thing in common: They both state that "Homo Erectus originated in Africa and expanded to Eurasia about one million years ago" (Jin, L. , 2000), but from here forward, the two theories differ greatly. The Out-of-Africa Theory asserts that following Homo Erectus' migration out of Africa, "modern humans evolved in Africa, migrated to Eurasia and replaced all populations which had descended from Homo Erectus" (Johanson, D. , 2001). This theory also states that the different "populations [of Homo Erectus] became reproductively isolated, [and] began to evolve independently" (Johanson, D. , 2001), making modern human variation a relatively recent phenomenon.
The Multiregional Theory "holds that modern humans emerged [directly] from populations of archaic hominids," which has led to this hypothesis being referred to as the "single origin model" (Balter, M. , 2007). In this model, "the emergence of Homo Sapiensoccurred throughout the entire geographic range where humans lived," and "natural selection in regional populations is responsible for the regional variants" (Johanson, D. , 2001).
Each theory has its share of evidence. Genetic studies in support of the Multiregional Theory show that "the genetic diversity of today's human populations is greatest in Africa and decreases steadily with distance from that continent"- a genetic bottleneck being created as "each group of migrants founded a new population" (Balter, M. 2007). Scientists in support of this model also sought evidence through the osteology of fossils. Research showed that "archaic human skulls resemble modern skulls from the same region to the extent that appeared to be incompatible with the [Out-of-Africa] theory" (Salter, F. K. , 2007). Lastly, researchers from the University of Cambridge "analyzed 4666 male skulls from 105 worldwide populations. Based on 37 measurements team reports that the diversity of cranial shape within a population falls off the further it is from Africa, as might be predicted by the Multiregional model" (Balter, M. , 2007). Unfortunately however, the "majority opinion among specialists favors the Out-of-Africa Theory" (Salter, F. K. , 2007).
Basic evidence for the Out-of-Africa theory goes off hominid fossils found in South Africa "that possess all or nearly all of the diagnostic skull [characteristics] of [Homo Sapiens]". These fossils are quite recent-as scientists imagine Homo Sapiens to should be- and all have traditionally been accepted as modern Homo Sapiens" (Tattersall, I. , 2009). According to research on Homo Sapien osteology, "the new H...