Scientists find evidence in the fossil record that seems to support both the Multiregional Evolution hypothesis and the Recent Out of Africa Hypothesis without a clear conclusion. Much of the problem comes from simple fossil identification -- changes that occurred within or between species are most often minor, and full skeletons are rarely (if ever) found, so even determining exactly what species a given fossil is evidence of at a certain place and time requires some subjectivity on the part of the researcher (Fonda 2001).
Even contentious results are liable to lead to further disagreements among other scientists. For instance, one recent study found evidence through similarities and patterns in modern humans' mitochondrial DNA that suggests -- though even the authors of this study admit its does not prove -- that there were at least two geographical and temporal locations in which populations of Homo sapiens and/or their evolutionary ancestors left Africa (Rowold et al. 2007). At first, this might seem like a major step forward, even with the validity of the findings somewhat in question. In reality, though, the results of this and similar studies can and have been used as evidence for and against both sides of the argument (Rowold et al. 2007). Each new piece of evidence seems to cast more shadows even as it begins to shed light.
There is some evidence, however, that does seem to support one theory over another. Recently, the tide has begun to shift somewhat from the Recent Out of Africa hypothesis to the Multiregional Evolution Hypothesis, as new genetic evidence emerges that suggest full evolution into Homo sapiens, as opposed to other early Homo sapiens varieties, did not occur until much later than previously thought (Wu 2004). Even this is not conclusive, however; the issue...
For this reason, genetic dating based on perceived changes in the human DNA molecule or mitochondrial DNA is considered highly suspect by many, rendering any association of such dates to fossils an obsolete step.
Conclusion
Given the length of time and breadth of study spent on the issue, it seems likely that the true geographical and temporal origins of Homo sapiens will never be established with full scientific certainty. Because the subjects being dealt with existed so far in the past, many assumptions have to be made in the gathering and analyzing of data, rendering the results wide open to many different interpretations. The fossil record and genetic information can both provide some insight into when, where, and how modern man evolved, but neither science can claim any hard facts as evidence to support any claim. Modern research attempts are often somewhat tainted by bias, as well, making the issue even more complicated. In the end, our beginnings may be just as uncertain as our future.
References
Fonda, R. (2001) Age and origin of the human species. Mankind Quarterly, 42:189-90.
Reethford, J. (2008). Genetic evidence and the modern human origins debate. Heredity, 100:555 -- 63.
Rowold, D., Luis, J., Terreros, M., Herrers, R. (2007). Mitochondrial DNA geneflow indicates preferred usage of the Levant Corridor over the Horn of Africa passageway. Journal of human genetics, 52:436-47
Xinzhi Wu. (2004) on the origin of modern humans in China. Quaternary International 117:131-40.
