Term Paper: Twenty Million Years Ago

Pages: 10 (3134 words)  ·  Bibliography Sources: 1+  ·  Level: College Senior  ·  Topic: Evolution  ·  Buy This Paper

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[. . .] erectus societies, replacing a more polygamous system where the largest, strongest males generally out-competed smaller males and left the most offspring." (Campbell, 712-13). This implies that by the time Homo erectus emerged, females were choosing mates based upon characteristics other than mere physical prowess; this too, could help to explain the success of the species.

In addition to the more advanced tools that Homo erectus employed, many scientists have suggested that the spread of such a species across Eurasia and into temperate climates suggests that he may have made use of another major advancement: fire. Still, this assertion is almost pure speculation -- growing only out of attempts to explain hew Homo erectus could have been so widely successful -- and may remain so because the tools that could have been used to make fire are not likely to leave traces: "It is possible that they used an instrument like a bow drill which involves constant rubbing of wood together. This type of evidence would not preserve well." (Class Notes 2005). Altogether, it is plausible that Homo erectus used fire for multiple purposes; there is some evidence that it was used to drive herd animals over cliffs some 700,000 years ago in China; yet there is little definitive evidence one way or the other (Class Notes 2005). Even so, the use of fire would supply a much needed explanation for how a species native to the warm climes of Africa could so rapidly have come to dominate much of the terrestrial world.

Nonetheless, there remain many difficulties with the hypothesis that Homo erectus should be thought of as a very near relative of the species that led to the modern Homo sapien. These difficulties are not primarily associated with the evolutionary path that the geologic record suggests; instead, there are many competing theories concerning the sequence of events that eventually led to modern humans. In other words, among paleontologists, it is fairly widely accepted that the fossils that fall under the header Homo erectus are very near the direct lineage that leads towards humans, but it is unclear as to whether Homo erectus can be considered a single species. This is very significant, because if it is not a single species, then it is more likely that modern Homo sapiens colonized Eurasia independently of the migration of Homo erectus. One trouble is thus summarized:

"Some paleontologists insist that the variation among them is no more than it is among Homo sapiens today, and therefore that all the specimens should be placed into one species, Homo erectus. Here is the problem. If hominids were spread widely but thinly over the Old World, the widely separated populations would tend to diverge in some characters, both anatomical and cultural." (Cowen, 362).

Consequently, it has been difficult for many experts to accept the notion that a single species of Homo erectus can be thought to have stretched from South Africa to Southeast Asia; accordingly, some prefer to classify African varieties of erectus as Homo ergaster. Understandably, this would be a somewhat easy assertion to uphold if the discussion was of anything other than possible ancestors of human beings. After all, it is counterintuitive to think that populations so geographically separated, and exhibiting such variation could ever be the same species. Yet, if they were indeed separate species, then how is it that Homo sapiens subsequently came to populate six of the seven continents and all be members of the same species?

In order to grasp the consequences of this question we must first define what a homo sapien is. To do this, the biologic definition of a species must be used: "a set of individuals who are potentially or actually interbreeding to produce fertile offspring." (Cowen, 43). Yet, this definition leaves the door open for many gray areas in nature: instances where it is impossible to determine whether animals are members of the same species or not. Lions and tigers, for example; when they do interbreed they produce fertile offspring, but it is unclear whether they would interbreed in nature freely. They no-longer coexist in the same habitats -- because of human actions -- so they are not clearly different species. Similarly, you could, based upon the biologic definition of species, claim that an individual born with a genetic defect who is unable to have children is not a homo sapien -- another gray area.

Ultimately, if we are to believe that the migration of Homo erectus comprised the temporal and geographical split that eventually produced differing races of Homo sapiens, then we must believe two things: first, Homo erectus is our direct ancestor; and second, that Homo erectus and modern humans must be the same species. After all, if a modern human and an ancient Homo erectus -- from this point-of-view -- could not have produced fertile offspring, then it would also be impossible for a modern American Indian and an African to produce fertile offspring. So clearly, whenever the geographical split occurred, it must have occurred within a population very genetically similar to our own.

Sechrest and Brooks note that with reference to plant and animal life in general, "Species diversity is unevenly distributed across the globe, with terrestrial diversity concentrated in a few restricted biodiversity hotspots." (Sechrest and Brooks 2002). In other words, of the millions of plant and animal species presently inhabiting the planet earth, a significant portion of them reside in geographically small expanses of land. The consequence of this approach to the issue of global diversity is, "If this history is disproportionately extensive, we may face losses of phylogenic diversity and/or evolutionary ancient lineages even more devastating than reflected by species losses alone." (Sechrest and Brooks 2002). Yet, the mere existence of Homo sapiens across the entire globe sheds some level of doubt upon such understandings of how biologic diversity must occur.

Our knowledge of human evolution after Homo erectus, however, is even messier than what paleontologists know of the pre-modern hominids. It has been postulated by some scientists that Homo erectus must have coexisted with modern humans as they migrated on their own across Eurasia and into Australia. It is thought, by these paleontologists, that a form of modern humans may have evolved only one million years ago in Africa; supposedly, this species is represented by fossils found in Spain which have been called Homo antecessor, and must have lived about 500,000 years ago (Cowen, 363). Soon after, "Around 400,000 BP, H. heidelbergensis was making beautifully crafted hunting spears in Germany." (Cowen, 363). It would seem that these species developed into Neanderthals in Europe, while Homo erectus still thrived in Asia. Next, as many theorize, modern Homo sapiens swept in, around 45,000 years ago, and out-competed all other groups into extinction.

This scenario seems to be at least somewhat backed-up by genetic evidence. Today, there is fundamentally very little variation across the human population; yet, there are compelling divisions between "African" and "non-African" types along many genetic lines (Cowen, 364). This observation suggests that the human beings who colonized Eurasia and Australia both broke away from the African population recently -- only a few tens of thousands of years ago -- and that they were a small, isolated population of their own. To geneticists, the evidence implies very strongly that modern humans are descended from a population of Homo that was not only very small 10,000 years ago, but had been very small for a long time beforehand (Campbell, 715).

Overall, the geneticists' line of reasoning explains a lot. First, it has been noted that modern human DNA varies very little relative to modern Chimpanzee DNA. This also indicates a very explosive adaptive radiation among humans as we spread across the globe. Such would not be the case if Homo sapiens, in the form of Homo erectus, had migrated out of Africa as early as 1.8 Ma. Additional credence has been afforded this theory with the recent analysis of Neanderthal DNA; it has been found to be relatively dissimilar to our own; thus, indicating that Neanderthals had colonized Eurasia well before human arrival.

However, this is not the only interpretation of the DNA evidence. For instance, if we look at Chimp DNA as being an analog to Human DNA, we should expect what could be called a species of humans as being far more diverse than we currently are. So, although Neanderthal -- and we can infer Homo erectus -- DNA is dissimilar, it is close enough that they could be considered the same species as modern Homo sapiens. In other words, the level of variation among Chimps, were it applied to humans, could easily account for the differences between Homo sapiens, Neanderthals, and Homo erectus. Accordingly, it is possible to imagine a single species of humans being genetically and geographically distributed along such lines 1 Ma. If this was the case, then approximately 10,000 years ago there must have been some event that… [END OF PREVIEW]

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