For thousands of years, there have always been conflicts within the scientific community. Is matter infinitely divisible, or composed of indivisible particles? Does the sun revolve around the earth, or does the earth revolve around the sun? Nowadays, we already know the answer to these two questions. But, there is still a great scientific question that needs to be answered: Where did modern humans, the Homo sapiens sapiens, come from? Within the scientific community, there are two opposing positions led by eminent scientists who absolutely hate each other. The multiregional hypothesis of human evolution, led Milford Wolpoff, posits that modern humans evolved simultaneously throughout the Old World, and stayed as a single species as a result of gene flow. The other position, known as the recent African origin hypothesis, which is led by Christopher Stringer, proposes that modern humans evolved in Africa, and then spread throughout the world, displacing the Homo erectus and possibly the Homo neanderthalensis. The former hypothesis is supported by fossil evidence, while the latter is supported by genetic evidence; indeed, the argument seems more like an argument between genetics and paleontology than anything else. As one shall see, both hypotheses have much support, yet also much criticism.

As mentioned earlier, the multiregional hypothesis, founded primarily on fossil evidence, proposes that modern humans evolved from Homo erectus around the Old World, and simultaneously, with the modern humans still remaining a single specie as a result of gene flow. There is much fossil evidence supporting this position, from all over the Old World. One of the most oft-quoted examples of evidence supporting the multiregional hypothesis is the Homo erctus fossil found in Zhoukoudian, a cave in China. This fossil, the so-called “Peking Man,” exhibits many morphological characteristics found in many modern day Chinese people. Among them are small frontal sinuses, reduced posterior teeth, shovel-shaped incisors, and high frequencies of metopic sutures. These characteristics, although found in fossils outside of Asia, are not typical amongst African and European hominid fossils, and are certainly not typical amongst modern Africans or Europeans. There has yet to be a non-Asian hominid fossil that displays all these characteristics. It seems as if there is a smooth transition from the Peking Man to the modern day Chinese. However, the hypothesis the Peking Man is the descendant of modern day Chinese and East Asians has come under criticism, which shall be examined later.

In addition to fossil evidence in China, there is also fossil evidence in Europe and Australasia suggesting that the Homo sapiens sapiens there either evolved from the Homo erectus there, or Neanderthals, or interbred with them. In Europe, among this evidence are the similar morphological traits found in both Neanderthals and later modern humans who came to inhabit Europe. These traits include the prominent shape and size of the noses of Neanderthals and European modern humans and a bony bridge covering the opening in the mandibular nerve canal. This bony bridge is of great importance, since its frequency seems to have diminished over time, suggesting a smooth evolutionary transition from Neanderthals to modern Europeans. Additionally, African fossils of modern humans very rarely have this bridge, suggesting a strong link between Neanderthals and modern Europeans. In Australasia, there also appears to be strong fossil evidence in support of the multiregional hypothesis. Early hominid fossils in Java, dating to about 1mya, have many morphological attributes found in modern humans living in the area, including thick skull ones, strong continuous browridges, and a second well-developed shelf of bone at the back of the skull. The humans who first arrived in Australia about 60 kya were modern humans, and also display many morphological features found in the aforementioned early Javan fossils. Proponents of the multiregional theory would cite this as evidence that the modern humans from Australia descended from the early humans in Java, rather than modern humans in Africa.

Although genetic evidence primarily favors the Out of Africa hypothesis, it would be inaccurate to say that there is no genetic evidence supporting the multiregional theory. Proponents of this theory would point to genetic studies on sections of the X chromosome, suggesting breeding between humans and other hominids. Probably one of the most paramount cases of genetic evidence in support of the multiregional theory comes from the “Mungo Man.” This fossil of an early modern human inhabitant of Australia dates to around 40 kya. This dating fits with the Out of Africa hypothesis, so it cannot be used as evidence for the multiregional hypothesis. What can be used as evidence for the multiregional hypothesis is a recent genetic study of the fossil. This study, conducted by an Australian National University graduate student in 1995, found that the Mungo Man was not descended from the Mitochondrial Eve (which shall be discussed in greater detail later on), the most recent common female ancestor of all humans. It is possible that the Mungo Man descended from another female ancestor originating in Africa whose line ended up dying out, therefore reconciling this study with the Out of Africa hypothesis. But, it is also possible that the Mungo Man descended from Homo erectus ancestors in Java, therefore giving more evidence supporting the multiregional theory.

Although the multiregional theory is corroborated with much evidence, both archeological and genetic, there is still much criticism leveled at it. Beginning with the Peking Man, scientists have noted that its physical features are found in only some Chinese people, and most Chinese people do not share these physical characteristics. Additionally, these characteristics can be found in fossils outside of China. However, as previously mentioned, there isn’t a single fossil outside of China that features every single one of these characteristics. Probably, the heaviest damage against the Peking Man comes from a genetic study done by Jin Li of Fudan University, in Shanghai. He and his team analyzed Y chromosomes of men around China and compared those results with men from Africa and Southeast Asia. Ultimately, he concluded from the study that modern humans migrated from Africa to Southeast Asia about 60 kya. These migrants then moved on to Southern China, and later, to Northern China. This contradicts the belief that the Chinese are descended from the Peking Man.

Regarding Neanderthals, there is also much criticism. Not only do mtDNA samples gathered from Neanderthals and modern humans show that the two are not closely related, but fossil evidence also offers much evidence against a multiregional model. There have been cases of abrupt technological advancements appearing in Europe during the disappearance of the Neanderthals and the arrival of the Cro-Magnon man. If the Neanderthals did evolve into modern humans, then one would not expect the technological advancements to have come so abruptly. Morphological traits seen in modern European humans are also absent in the Neanderthals. This includes the overall build and the tibia to femur ratio. In the fossil record, these morphological traits did not appear smoothly as predicted by evolution, but rather abruptly as modern human fossils began appearing.

A large problem with the multiregional model is the assumption that during the time period when the Homo erectus began evolving into Homo sapiens in Africa and Asia, there was a lot of gene flow in order to keep the Homo sapiens as one species. In order for there to have been a lot of gene flow, there needed to have been large populations to keep the genes flowing. However, during a period of one and a half million years, there wasn’t a single Homo erectus fossil. Although fossilization is rare, it is unlikely for a highly populated area to yield no fossil for a period of one and a half million years. It seems as if the gene flow idea does not stand up very well. Indeed, there may well have been gene flow during that time period, but probably not enough to keep the Homo sapiens as one species if it evolved simultaneously in Africa and Asia.

After examining the multiregional hypothesis, readers can now move on to the Out of Africa hypothesis. The Out of Africa hypothesis, as mentioned earlier, posits that modern humans evolved in Africa and then spread itself throughout the world, replacing the hominid species there. The evidence for the Out of Africa theory is both genetic and archeological. In terms of genetic evidence, most of it comes from the Mitochondrial Eve. Similar to the nucleus, the mitochondria also has its own DNA, known as mtDNA. This DNA, unlike the nuclear DNA which gets “tampered” with every time reproduction occurs, is passed on only from the mother, and is therefore consistently the same. The mitochondrial DNA also undergoes a steady and quick rate of mutation, allowing scientists to develop a molecular clock. Allan Wilson and his team at the University of California at Berkeley collected samples of mtDNA from 147 women around the world. Using a molecular clock, Wilson determined that the modern human mtDNA arose in Africa about 150 kya, lending evidence to the Out of Africa hypothesis. His dating and the implications of the test have been severely criticized, which will be discussed later. Not only does Wilson’s study yield a mitochondrial Eve, but it also yields another piece of crucial evidence in support of the Out of Africa hypothesis. From his study, Wilson was also able to conclude that there was much greater genetic variation in Africa than anywhere else. This implies that modern humans have been in Africa far longer than anywhere else. Additional genetic studies have yielded a Y chromosome Adam, which is the most recent common male ancestor of all humans, who lived in Africa around 60 kya. Once again, genetics seem to support the Out of Africa hypothesis.

There are even ongoing genetic studies corroborating with the Out of Africa hypothesis. A recent detailed study comparing 650,000 genetic markers in thousands of individuals bolsters the Out of Africa hypothesis. From the study, scientists have concluded that genetic variation decreases as one moves further and further away from Africa. An even more recent study conducted by researchers from Oxford, Stanford, and Tartu revealed that Australian Aborigines and Melanesians share genetic features linked with the modern humans who left Africa 50 to 70 kya.

From fossil evidence, one can also see much support for the Out of Africa hypothesis. For one, the oldest modern human fossil comes from Africa. As one moves further and further away from Africa, the oldest modern human fossils in those regions are much younger than the oldest modern human fossils in Africa and the Middle East. For instance, the oldest modern human fossil in Australia is about 50 kya. The oldest modern human fossils in Asia are from 20 to 30 kya.

Not only does the dating of fossils seem to favor an Out of Africa hypothesis, but the structure and nature of the fossils themselves favor this hypothesis. As previously mentioned, the tibia to femur ratio of modern European human fossils differs from the ratio of Neanderthals fossils. This ratio is important, as it is directly proportional to the climate conditions of the individual. The ratio for Neanderthals clearly indicates that they came from colder conditions. However, the ratio for the Homo sapiens fossils in Europe indicates that they came from warmer conditions. This clearly suggests that modern European humans did not evolve from Neanderthals. Further dating evidence also suggests the unlikely hood of modern humans having evolved from Neanderthals. Tools associated with humans have been found in Israel, dating to around 100 kya. This is about 40 to 60 kya older than the oldest Neanderthal fossil in Israel.

Archeological evidence in Europe shows the appearance of Aurignacian technologies around 45 to 35 kya, at about the same time the Neanderthals began disappearing. Not only is this technology commonly associated with Homo sapiens, but it appeared so abruptly in Europe without any clear antecedents that it is very unlikely to have evolved from Neanderthals. In addition, dating shows that it first appeared around Eastern Europe and moved westward. This correlates with the hypothesis that modern humans came to Europe through the Middle East.

Although the Out of Africa hypothesis is supported by a lot of evidence, it too isn’t without criticism. Of greatest criticism is the mitochondrial dating that yielded mitochondrial Eve. For one, the mutation rate is not exactly known, and some estimates have placed the age even as far as 850 kya. This, however, is still much later than 2 mya, which is when Homo erectus began leaving Africa. Additionally, the mtDNA is only a small fraction of total genetic material. The rest of human genetic material came from the many individuals who lived during the same time period as Mitochondrial Eve, and may have been spread over a wide area. As for Africa being more genetically diverse than other areas, this can be explained by the fact that non-African populations may have been smaller or experienced large drops in numbers, resulting in smaller genetic diversity.

Another aspect commonly criticized is how the modern humans managed to replace all existing Homo erectus and Neanderthals in the area? Currently, proponents of the Out of Africa model are not entirely sure how modern humans managed to replace those other humans. There are several possible reasons. One, modern humans were capable of complex language that gave them an evolutionary advantage. Although scientists debate whether or not the Neanderthals were capable of language, there is no doubt that the language of modern humans is much more complex. Two, modern humans were much more intelligent. This is evidenced in their tools, organization, and even cave art. Although Neanderthals engaged in art, examples of art increased at a dramatic rate after the emergence of modern humans. Art in it of itself does not facilitate survival, but it does show abstract thinking and intelligence, which would surely benefit survival.

A third aspect commonly criticized of the Out of Africa model is the morphological similarities between Homo erectus and Neanderthal fossils of a particular area and the fossils of the modern humans who later came to inhabit that area. Although those fossils shared many differences, there are still many similarities that are undeniable. One explanation could be parallel evolution. If natural selection favors certain morphological features in one species, it isn’t too much of a stretch to say that those same features could have been developed in unrelated species. After all, mammals living in the arctic all have white fur. In some cases, however, the similarities are so uncanny that it seems very probable that there was at least some gene flow involved.

Of these two theories, the Out of Africa hypothesis seems to have much more support, both genetically and archeologically. Given all this evidence, it seems very hard to deny that humans evolved from Africa and spread to other places around the world. But, some ideas of the multiregional hypothesis are certainly very valid, such as gene flow. This seems to be the only way, along with parallel evolution, to explain morphological similarities between other hominid species and Homo sapiens living in an area. For instance, the Neanderthals may well have interbred and ultimately assimilated into the Homo sapiens. Or, at least their more “fit” genes have. This is position is fairly controversial too, but it seems more reasonable than any of the two extremes.

Who knows what the ultimately correct answer may be? Even today, scientists are trying to map out the hominid journey across the world. The Genographic Project, funded and headed by National Geographic, is an ambitious five year study started in 2005 that attempts to map out the human migration patterns by collecting and analyzing hundreds of thousands of DNA samples. Perhaps, the answer to this great scientific question lies in this project. As scientists uncover more and more evidence, they come closer and closer to finding the correct answer. Whichever theory may be correct, the Out of Africa theory, and multiregional theory, or a combination thereof, all of them support the unity and relatedness of mankind.