Modern Human Origins Jay Hamilton



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Modern Human Origins

Jay Hamilton

There are, at this time, two main theories as to where modern humans originated. First, the theory of Multiregional Evolution and second, the African Replacement theory. Both have merit and evidence supporting their position, as well as Anthropologists on both sides of the debate. My intention with this paper is to persuade the reader on the validity of one of the theories. However, in order to do so, I must explain the basic tenets of each side and discuss the evidence supporting them. We will first walk through the multiregional theory and learn of its supporting evidence. Second, we will look at the out of Africa or replacement theory. Finally, a brief discussion, contrasting each side, sharing my personal view based my interpretation of the evidence. Throughout, I will attempt to be impartial and fair in representing each side. However, due to my lack of expertise, time constraints and limited resources, it is possible that important data will be missed or even misrepresented. It would be up to each person to study beyond the limited scope of this paper if additional information is desired.

Multiregional evolution theory. What is it? It is the idea that modern humans evolved over a large and diverse geographic area, in large numbers. This is not a non-trivial area, being a geographic range estimated at 35,000,000 km2 and is a large group of breeding sets as high as 500,00 couples (Eller, 807). Because of the large area in which homo sapiens, neanderthals and denisovans lived, we will need to apply some conditions for this theory to come together. Professor Milford H. Wolpoff, the leading expert on the multiregional theory has defined those conditions. First, we must deny that the earliest modern homo sapiens evolved exclusively in Africa. Second, there would need to be a fair amount of gene flow between the different populations. In this way, speciation would not occur in the individual groups of early humans (Jurmain, 284). As far as evidence is concerned, we would want to look at the genetic code of our not so distant relatives. Advancements in DNA decoding, coupled with quality genetic material from early homo sapiens, neandrathal and denisovans have allowed us to compare them to living humans. What we find is a small percentage of DNA in humans of European descent is neandrathal. Also, in Malaysia we see humans with denisonovan DNA. This gives credence to the idea that gene flow did occur amongst some populations. However, the fossil record is not very kind to this theory. At this time fossils point to homo sapiens originating in Africa. This has not dissuaded many people from this theory though, they just claim that the early fossils of home sapiens have not been discovered yet.

Now we move onto our next theory, the replacement model. There are different variations of this, but they all share the same basic tenant: homo sapiens evolved first in Africa and then spread throughout Asia and Europe. This would have been a gradual move, taking hundreds of thousands of years to complete. Along the way, it is believed that homo sapiens out competed or killed off their hominin cousins. The fossil record shows the gradual relocation of early humans as they spread out of Africa. So, the timing seems right. However, the latest genetic evidence shows interbreeding with neanderthal man. This would fly in the face of a total replacement theory, because homo sapiens would be a different species than neanderthal and not be able to produce viable offspring. That said, we must now assume that they were all part of the same species (Relethford, 555).

So, where do I stand? This is a tricky debate and I am generally a contrarian. That leads me to want to root for the Multiregional theory. With its blatant lack of evidence and incredibly bold speculation, it would be easy to write it off. But, when I began peeling off the layers, there seems to be more substance to it. The first, and most important, ‘gotcha’ is the interbreeding. In order for later breeding between the different groups we would need one of two things to be true: either, multiple species evolved completely independent of each other, were physically different, but genetically compatible. Or there was earlier interbreeding than explained in the replacement model. The latter is much more realistic. The second, much less important, ‘gotcha’ is the absence of neanderthal DNA and fossil records in Africa. In order for the genetic compatibility to take place, they would have needed to be close together during the speciation process, because they are subs of the same species. This would also be true of denisovans as well. However, it is with a sad heart that I must admit that there is a fatal flaw in this theory that I cannot overlook: almost all fossil evidence is against it. Lack of evidence is not evidence and the burden of proof lies squarely on the shoulders of the individual making the claim. So, I will fall back to the more popular and feasible theory of the replacement model. It seems that that genetic evidence is continuing to show the validity of it and I would be amiss if not to jump on the bandwagon (Ghirotto, 484).

Reference List

Ghirotto, S., Penso-Dolfin, L., & Barbujani, G. (2011). Genomic evidence for an African expansion of anatomically modern humans by a southern route. Human Biology, 83(4), 477-489

Wang, C., Farina, S. E., & Li, H. (2013). Neanderthal DNA and modern human origins. Quaternary International, 295126-129. doi:10.1016/j.quaint.2012.02.027

Eller, E., Hawks, J., & Relethford, J. H. (2009). Local extinction and recolonization, species effective population size, and modern human origins. Human Biology, 81(5/6), 805-824.

Relethford, J. H. (2008). Genetic evidence and the modern human origins debate. Heredity, 100(6), 555-563. doi:10.1038/hdy.2008.14

Jurmain, R.,Kilgore, L., Trevathan, W. (2013). Human Origins Evolution and Diversity. Mason, OH: Cenage Learning.

Multiregional origin of modern humans (n.d.). In Wikipedia. Retrieved from http://en.wikipedia.org/wiki/Multiregional_origin_of_modern_humans

Denisovan (n.d.). In Wikipedia. Retrieved from http://en.wikipedia.org/wiki/Denisovan

Milford H. Wolpoff (n.d.). In Wikipedia. Retrieved from http://en.wikipedia.org/wiki/Milford_H._Wolpoff



ePortfolio link: http://jhamil22.wordpress.com/2014/04/30/human-origins-paper/

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