The origin of Homo sapiens

The origin of modern Homo sapiens is very controversial. Some early species, such as Homo ergaster, Homo erectus, Homo neanderthalensis, Homo heidelbergensis, and possibly even Homo antecessor, are all possible ancestors of the species Homo sapien. Recent studies have shown that Homo sapiens most likely descended from populations in the Homo ergaster and Homo erectus group. Modern Homo sapiens first appeared in the fossil records about 100,000 years ago in Africa and Israel. Later fossils were found also in Europe and Asia.
Scientists have debated three different models for explaining the origins of modern humans. These are the African replacement model, the multi-region model, and the assimilation model.
The Recent African Origin model was given a huge boost in 1987, when a paper published in the scientific journal Nature, Mitochondrial DNA and Human Evolution, rocked the palaeoanthropology world. It showed that part of our genome, inherited only through mothers and daughters, derived from an African ancestor about 200,000 years ago. This female ancestor became known as Mitochondrial Eve.Although the paper was contested, the results strongly supported the views that the Natural History Museum’s human origins expert Chris Stringer and others had been developing that we had a recent African origin. In the following decade, more genetic data both from recent human people and Neanderthal fossils were collected supporting the Recent African Origin model. The idea gained momentum and with it the view that when modern humans began to leave Africa around 60,000 years ago they largely or entirely replaced other archaic human species outside the continent.
The Multi-regional model, by contrast, put forward parallel lines of evolution in each inhabited region of Africa, Europe, Asia and Australasia, glued together by interbreeding across the human range.Under this model, there was no real origin for the modern form of Homo sapiens. A feature like a chin might have evolved in a region such as Africa and spread through interbreeding, followed by selection if it was an advantageous characteristic. Another feature, like our high forehead, might have evolved elsewhere and then spread through interbreeding.
Another group of scientists embraced a third theory: the Assimilation model. Like the recent African origin model, this gave Africa a key role as the place where modern human features evolved, but it imagined a much more gradual spread of those features. Under this view, Neanderthals and archaic people like them were assimilated through widespread interbreeding. This meant that the establishment of modern human features occurred via a blending of populations rather than a rapid replacement.
Information acquired from: http://www.nhm.ac.uk/nature-online/life/human-origins/modern-human-evolution/where/index.html
So which of these models is right? It is unknown. Though there are many hypotheses and evidence of many different results, scientists do not fully understand the origins of the species Homo sapien.
For more information about this topic:
http://anthro.palomar.edu/homo2/mod_homo_4.htm