The origins of the modern human species

Homo Sapiens

The question of the origins of the modern human species, Homo sapiens, has two interconnected facets that require different yet concurrent scientific approaches to achieve more accurate information. The geographical origin of the species and the timeline of the species’ spread to other part of the globe constitutes one of the major ways to trace the origin of Homo sapiens. The other avenue of scientific pursuit is in tracing the genetic changes as they occurred in the distant evolutionary past. Both areas of research have inspired contention among experts. This article reviews some of the current pertinent literature pertaining to past, current, and ongoing research in these areas in an attempt to form a better understanding of the origins of Homo sapiens and the science that has led to this conclusion.

Introduction

The current geographical/anthropological arguments currently subscribed to by most scientists for whom this is an area of concern are the Recent Out of Africa hypothesis and the Multiregional Evolution Hypothesis, though there are also several other less accepted theories (Wu 2004). Basically, the argument of the widely held Recent Out of Africa Hypothesis claims suggests that modern man, Homo sapiens, evolved from other Homo precursors in Africa, and that a single population of Homo sapiens left Africa fairly recently in historic/geological terms, and that this population spread around the world and continued to evolve slightly into the observable ethnicities today (Wu 2004). The Recent Out of Africa Hypothesis does not give a complete and consistent answer to the issue of the origin and spread of Homo sapiens, however; aspects of this hypothesis are debated even amongst adherents.

The other major competing theory, the Multiregional Evolution Hypothesis, also believes that at some point the ancestors of modern humans came out of Africa and began to spread, and then developed into the various ethnicities of Homo sapiens independently in several different regions in Africa, Asia, and the Middle East (Wu 2004). The data used in the field consists mainly of fossil records, which are notoriously incomplete and therefore, despite the amount of knowledge fossils can provide to scientific researchers, unreliable means of ascertaining the true evolution of most creatures, including Homo sapiens. Certain geological information can also be used in dating fossils as well as modeling weather patterns to propose times that migration might have been facilitated or necessitated, which when combined with the fossil record might provide more conclusive evidence (Wu 2004). The information so obtained, however, can be interpreted in many ways, leaving the problem still largely unsolved. This is where the hopeful solution of Homo sapiens sapeiens origins becomes genetic.

Genetic information is useful in several ways when attempting to discern the origin of any species, including Homo sapiens. Because the standard rate of genetic change has been fairly well established, many experts believe that the years when various branches of the Homo sapiens family tree diverged or evolved (Relethford 2008). This information can be used in tandem with the fossil record in an attempt to date fossils and so determine where certain evolutionary steps occurred (Fonda 2001). In addition, genetic testing on people indigenous to regions of suspected Homo sapiens origins has led some to support one hypothesis or the other based on similarities or differences in DNA structure (Rowold et al. 2007).

Discussion

The issue with all of the current information available from both the paleontological/geographical perspective and the genetic perspective is that most if not all of it can be validly interpreted in different ways, though scientists in each camp firmly believe in the correctness of their own beliefs and point out what they perceive to be fatal flaws in the reasoning of the other side (Fonda 2001). 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 of exactly when genetic changes occurred cannot actually be established with any certainty, and many scientists have raised objections to the many assumptions the presumed rate of evolutionary change makes (Fonda 2001, Relethford, 2008). 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.