Summary
The online proceedings of the National Academy of Sciences released research findings from Uppsala University that people in East Asia share genetic material with Denisovans. The significance of these findings is related to the fact that certain species of “archaic humans” did not proliferate in isolation until they were replaced by modern humans. The said researchers said that hybridization occurred at several points in the evolution of humans and at the same time traces can be found in several places in the world.
The conclusion that “hybridization occurred on the East Asian mainland was based on the study of genotype data in order to obtain a larger data set” (ScienceDaily 1). But the findings were anchored into a particular observation: “individuals from mainly Southeast Asia have a higher proportion of Denisova-related genetic variants than people from other parts of the world such as Europe, America, West and Central Asia, and Africa” (ScienceDaily 1). It is also based on the assumption that this hybridization process occurred “long after the branch that became modern humans split off from the branch that led to the Neanderthals and Denisovans some 300,000-500,000 years ago (ScienceDaily 1). But researchers do not possess solid scientific evidence to prove this claim prompting one of the researchers to say that he is thankful for the complete genome mapping of modern humans and more analysis of fossil material to understand human prehistory with greater accuracy.
Scientific Evidence (evidence used)
According to the researchers, “We found that individuals from mainly Southeast Asia have higher proportion of Denisova-related genetic variants than people from other parts of the world, such as Europe, America, West and Central Asia, and Africa” (ScienceDaily 1). In other words there is no evidence to show that the Denisova-related generic traits are found in other significant population centers in the world. Thus, they were able to surmise that there is only one explanation and that is hybridization. The researchers did not explain the specific mode of delivery of the genetic material through hybridization thus it must be assumed that the Denisovans in Siberia were able to travel to Southeast Asia and intermarry with the local population.
At the same time it can also be argued that Denisovans intermarry with ancestors of modern humans in Europe before they migrated to Asia. On the other hand it can also be argued that the Denisovans and modern humans came from one source. But the researchers immediately made the conclusion that “gene flow from archaic humans also occurred on the Asian mainland” (ScienceDaily 1). But this is conclusion is based on limited access to archaeological information and limitations in the capability to analyze genetic information of fossilized human remains as well as present human populations.
Questions about Research
This particular research answered the question regarding the connection between “archaic humans” and modern humans. Based on the information there is basis to the conclusion that there is interaction between two species. This also serves to answer a question pertaining to the human evolution which is the missing link that connects modern humans from supposedly much simple life forms. This research can partially answer that question. In other words these different species did not evolve in isolation but interacted with each other. Nevertheless, it is not enough to provide the missing link because this study simply addressed the fact that modern humans in Southeast Asia exhibit genetic traits that are supposed to be unique to Denisovans.
Although the research findings shed light on certain issues regarding human evolution, it also leads to more questions. Consider the problems that can arise from this statement: “Our study covers a larger part of the world than earlier studies” (ScienceDaily 1). It means that their conclusion can change after the discovery of more fossil evidence as well as the collation of data from other sources such as from projects related to genome sequencing.
It is a problematic issue because research projects can yield different results based on the quality of evidence at hand. In the case of human evolution it is important not only to focus on one bone fragment but several sources of genetic material that covers a wide range of the population. It is easy for researchers to ignore evidence that does not favor their theory.
Another problematic issue stems from this statement: “Hybridization took place at several points in evolution, and the genetic traces of this can be found in several places in the world” (Science Daily 1). It must be proven first if hybridization did occur or the modern humans in Southeast Asia simply migrated from Siberia where the Denisovans were said to have originated. A migration can explain the presence of genetic traits of Denisovans in 21st century Southeast Asian people as much as the assertion that Denisovans crossed Russia to intermarry with tribal people thousands of years ago.
Aside from the need to determine if hybridization or migration is the real culprit in the discovery of “archaic human” traits in modern Southeast Asian people, another important feature of this study that has to be scrutinized pertains to extensive use of genetic information. One of the confusing aspects of the research is on how researchers were able to arrive at their conclusion.
Researchers used to related terms genotype and genome. They also mentioned genotype data and complete genomes. These phrases are related in terms of the study of genetics but they are also entirely different when it comes to the complex study of human traits and human evolution. A genotype means observable characteristics of a species that is linked to its DNA or chromosome. A complete genome on the other hand suggests that the researchers were referring to genome sequence. A genome sequence yields a different set of data when compared to the study of genotype. A genome sequence simply tells of the genetic material but not how it was expressed.
It is therefore important for the researchers to clarify what they mean when they said that they based their conclusion on genotype and complete genome. It would be much better if they wait for the complete genome mapping of modern Southeast Asian people and compare it to complete genome mapping of the Denisovans.
Another critical issue of this research arose from the following assertion, that they found “higher proportion of Denisova-related genetic variants” in the target population as compared to people from other parts of the world. This is a statement that requires clarification. First of all they claim that there is higher proportion of Denisova-related genetic variants in this area but the question is how wide was the scope of their research? Their findings may lose its significance if they will discover that the same evidence was found in China. As many are aware, Russia is closer to China and therefore it would have been easier for the Denisovans to migrate to China and intermarry with the local population. From China it would be relatively easier to migrate to Southeast Asia.
Secondly, they claim that there is higher proportion in Southeast Asia as compared to other lands. Thus, it means that other people groups from all over the world exhibit the same characteristic traits but in lower proportion. But what if the scope of the research is extended much further? What if the funding of the research is significantly increased in order for researchers to gather more data. It is possible that as the number of participants is increased the conclusion can be altered.
In addition the researchers must clarify what they mean by the phrase that says this genetic variant are Denisovan related. It can be interpreted to mean that researchers are not yet able to provide a clear description of the genotype related to Denisovans. At the same time, since the genotype is related only to the Denisovan and not a complete expression of Denisovan characteristics then there can be another explanation for existence of this particular physical feature. It is also critical to determine if this physical feature is a product of hybridization and not adaptation.
It is also important to clarify the assumption needed for human evolution to have occurred. It is linked to the assumption that there was a complete evolution that replaced all traces of “archaic humans” and resulted in the creation of a new species called modern humans. A related idea is that “non-African gene lineages were replaced by African gene lineages during the Late Pleistocene is rejected by observations (Harvati & Harrison 231). Thus, there is a need to reconsider the idea that hybridization had occurred and replace it with another hypothesis that instead of hybridization, a successful migration had occurred. Consider the following observations:
Within the Late Pleistocene, it is probable that the global population grew by tenfold or more, because of increases in geographic range and population density. Most obviously, during the past 50,000 years, human population colonized areas that previously had no human inhabitants. These areas include the northern tier of Eurasia, the Arctic, Beringia and the Americas, the Melanesian archipelago, Japan, the Philippines, Australia, and many others (Harvati & Harrison 229).
It has to be highlighted that the area mentioned in the study is known to have no inhabitants for a significant period in human history. Thus, these areas were populated only through migration. It is therefore a crucial factor to consider in the claim that Denisovans intermarried with the modern humans especially those that can be found in Southeast Asia.
Conclusion
The researchers must be commended for the discovery of Denisovan-related genotype expressed in a modern human population located in Southeast Asia. This is a significant discovery because the Denisovans are considered a part of a group called “archaic humans.” But it has to be clarified if the expression of a particular genotype is the result of hybridization or migration. If it is the result of migration then it creates a ripple effect when it comes to the evolution of humans. It can be argued that humans did not evolve from “archaic humans” but a mere byproduct of adaptation.
Works Cited
Harvati, Katerina and Terry Harrison. Neanderthals Revisited: New Approaches and Prespectives. New York: Springer, 2007, Print.
ScienceDaily. Shared Genes with Neanderthal Relatives: Modern East Asians share Genetic Material with Prehistoric Denisovans. ScienceDaily, 2011. Web.