The Colonization of Sahul and the Colonization of the New World - Essay Example

Order 247649 This discussion explores how and when the first humans travelled to the previously unoccupied continental land masses of Australia (Sahul) and the Americas (the New World), and analyses the impact that these humans had on the existent megafauna. Humans are widely thought to have caused widespread extinction of the megafauna on these two continents because their arrival coincided with the mass extinction. The other contributing factor which has also been widely attributed to the megafauna extinction is climate change (Wroe et. al. 2004) Homo Erectus which populated Eurasia did not reach the Sahul or the New World unlike the later Homo Sapiens genus. Homo Sapiens are believed to have undertaken their migration from their origins in Africa from about 50,000 years ago (O’Connella & Allen 2004). These late Pleistocene migrations coincided with the end of the earth’s most recent period of glaciations (Ice Ages). The accumulation of vast amounts of ice in the glaciers resulted in punctuated drops in the sea level of up to 100m allowing easier access to the previously uninhabited continents. When the Homo Sapiens left Africa they are believed to have migrated east toward India and then south east along the coast of Asia until they reached Australia between 45,000 to 42,000 years ago (O’Connella & Allen 2004). At that time, due to the much lower sea level, most of martime Southeast Asia formed one land mass – known as the lost continent of Sunda. Following the coastal route southeast they would have reached the channel between Sunda and Sahul (present day Australia and New Guinea). This channel, between the Sahul and Sunda (known as the Wallace Line) must have been traversed by the technologically more advanced Homo Sapiens whereas the earlier Homo Erectus never traversed it (O’Connella & Allen 2004). It is presumed that they used rafts of some sort to traverse the channel. The close chronological coincidence of the arrival of humans capable of hunting megafauna and the Pleistocene mass extinction around 40,000 years ago in the Sahul lends support to the hypothesis that humans were in some way a causal factor. These megafauna, having evolved in the absence of human predation are thought to have been particularly vulnerable to the arrival of humans in the form of Homo Sapiens. The Megafauna had few other predators and because they evolved largely without significant predators. Models of migration to the New World are more divided. The reliable evidence currently available suggests a north western migration of people who crossed from Siberia into Alaska. At the time, due to lower sea levels, the lost continent of Beringia connected North America to Eurasia. Whilst the bulk of evidence points towards findings related to the Clovis culture (circa up to 13,500 years ago), there are also the controversial findings in Monte Verde, Chile where human presence as early as 33,000 years ago is indicated – this earlier date has not yet been widely accepted by the academic community. The mass extinction of megafauna around the time of the Clovis findings suggests that, as earlier in Australia, that these people played a role in the extinction of the megafauna. The Clovis were Homo Sapiens thought to be capable of hunting large prey. The “Overkill Hypothesis” was proposed in 1969 by Paul S. Martin and was primarily concerned with the New world evidence of megafauna extinction. While the extinction of the megafauna had earlier been explained by the “Hunting Hypothesis”, Martin’s new “Overkill Hypothesis” sought to explain this phenomenon over relatively short period of time. The extinction of 80% of the North American megafauna over 1000 years shortly after the arrival of humans is the core of the hypothesis. The Clovis culture was thought to be big game hunters who used their stone fluted projectiles for hunting. While the hypothesis enjoys much support, the evidence to support it is somewhat tenuous. What has thrown doubt on the hypothesis has been linked to the actual processes which would have made the rapid depletion, through hunting, of the endemic megafauna possible within the technological and population capacities of the early migrants to these continents. The two most common mechanisms proposed are direct predation (“overkill”) and environmental modification via the use of fire. The overkill option in the sahul has a complete absence of any direct evidence of human predation on megafauna. In addition to this it is almost certain that the populations of early human in the Sahul were too low to have caused any damage to the megafauna through direct predation. Whilst the fire hypothesis seems more plausible in the Sahul, it has been largely refuted by the observation that the sharpest changes in Sahul vegetation evident over the last few hundred thousand years “are climate - rather than human-driven, and that clear-cut prehistoric human impacts unconnected with agriculture are difficult to identify in the Sahul pollen record” (O’Connella & Allen 2004, p 848). In terms of the Sahul, the observation that “Tasmania which was cut off from the mainland by relatively high sea levels until after 37,000 years ago suggests that humans were not the cause of the rapid megafaunal extinction in the Sahul. (O’Connella J.F.) . O’Connella conclude that “despite the apparent coalescence of certain provocative chronometric data, the case for rapid continent-wide extinction of megafauna as a result of human colonization has yet to be made” (O’Connella & Allen 2004, p. 850). While the “Overkill hypothesis” in terms the New World it is an attractive hypothesis to explain the megafaunal extinction in terms of chronologically, it has been criticized for being conjecture as opposed to a scientific hypothesis based upon evidence. There is no evidence that the Clovis were specialist big game hunters (Grayson & Metzer 2003). Martin’s “Overkill Hypothesis” stands on three rather precarious legs. The first is comparing the record of the human impact on islands to that of continents. There is no evidence to suggest that hunting alone caused island extinctions – as in New Zealand where extinctions took 900 years and were not only due to hunting (D.K. Grayson). The second is that the Clovis were specialist hunters. The archaeological record disputes this conclusion and Martin tried to account for this by stating that the killing took place so fast that it would be unlikely to find much evidence for it (D.K. Grayson). The third is that the extinctions occurred 11,000 years ago in conjunction with the arrival of the Clovis hunters. A closer look at large mammal extinctions shows that they occurred in a widespread fashion “at the end of the Pleistocene with or without Clovis, with or without the presence of human predators”. (D.K. Grayson). The “Overkill hypothesis” although seemingly attractive is a weak hypothesis because it rests on conjecture without much empirical evidence to support the hypothesis. In this respect it is not scientific and it would be better to with-hold judgment than support it merely because there is currently no other definitive alternative. A second competing hypothesis is that the mass extinction is due to climate change. This is hypothesis surmises that the termination of the Pleistocene ice age might be an explanation for the extinctions. There were however multiple Ice Ages in the evolutionary history of many of the megafauna, it is therefore rather implausible that only after the last glacial would there be such extinctions. This is particularly true for Australia where evidence suggests that the prevailing climate (40,000 – 50,000 BP) was not dissimilar to that found today and that the megafauna had adapted to arid conditions. Moreover evidence indicating the same short time period of extinction which is closely correlated to the arrival of humans, refutes the climate hypothesis (Wroe et. al. 2004) In the New World the increased temperature associated with the termination of an ice age, where between 15,000 BP and 10,000 BP a 6°C increase in global mean annual temperatures occurred, could more plausibly be linked to the cause of the extinctions. Here the thermal stress on the cold-adapted mammals may have caused the animals to die of heat exhaustion. Larger mammals, with a reduced surface area-to-volume ratio, would be far more vulnerable than smaller mammals (Wroe et. al. 2004) Shortcomings of the Temperature Hypothesis have been underscored by subsequent research which has shown that the annual mean temperature of the current interglacial that we have seen for the last 10,000 years is no higher than that of previous interglacials. If the same megafauna survived similar temperature increases, temperature increases alone are not a sufficient explanation (Wroe et. al. 2004). Evidence of the survival of numerous species, such as the mammoth, on islands ling after the mass extinction suggest that climate change alone could not have caused the mass extinctions. It is more likely that they survived on these islands because they offered refuge from human predation. Island populations should be more sensitive to climate change because they prohibit migration to more suitable micro-climates (Wroe et. al. 2004) If climate had a role to play then why did large continents feature mass extinction while some islands did not? One answer to this problem proposes that increased continentality — hotter summers and colder winters — or related changes in rainfall caused the extinctions. Apart from the pressures associated surviving these extremes, the subsequent changes in vegetation may have affected the availability of suitable foods for the megafauna. There have been other climatic causes which have been posited to have an effect such as changes in rainfall, changes in vegetation etc. but these alone do not seem to offer conclusive evidence. Another hypothesis is that the mass extinction may have been caused by the introduction of a disease introduced by humans but evidence of such a disease has been found. The situation as it stands is that although there have been many causes attributed to the demise of the megafauna, no single cause can be found. It is likely that there were a combination causal factors. Some of which may have had greater influence than others. It should be noted that earlier hypothesis tended to try to find single causes. This may be attributed to the development of science at the time. While they have all increased our understanding of the problem none have been able to conclusively answer the problem. This is largely due to the scarcity of evidence where some of the hypothesis have very little concrete evidence to be able to back up their assumptions. The archaeological record is at best tenuous and open to significant interpretation, especially when trying to understand the lifestyles of these early cultures and how they interacted with the environment. For example the Clovis culture is more likely to be more closely aligned to contemporary hunter-gatherer societies who are capable in big game hunting but do not specialise. Support for this could be found in that these groups seem to have migrated along coastal routes where there is a greater biodiversity of foods. Humans have been so successful precisely because they are not specialised feeders and therefore more adaptable to changes in their environment. The “Overkill Hypothesis” seems to posit a much higher technological capacity for being able to hunt large animals than the archaeological record seems to indicate and the fact that Martin suggests that the lack of evidence tends to prove his assumptions cannot be taken seriously if any scientific rigour is to be maintained. This discussion should illuminate the current debate about humans’ effect on global warming. The mere coincidence of observations is not sufficient to explain a scientific hypothesis. It is rather necessary to understand the mechanisms which may lead to humans to be able to effect massive climatic changes on the earth. It has been seen that the average temperature of the earth has not been constant during the recent past (in terms of geological time). It is evident that scientific investigation becomes ever more speculative where the evidence is scarcer. This should not be seen as a weakness in the method because it is this very creative speculation which guides new research and refines the debate. The ‘Overkill Hypothesis” seems to have come at a time when contemporary humans themselves where realising the effects they could have on their own environments. Works Cited D.K. Grayson & D.J. Meltzer. "A requiem for North American overkill." Journal of Archaeological Science (2003). O’Connella J.F. & Allen J. "Dating the colonization of Sahul (Pleistocene Australia–New Guinea): a review of recent research." Journal of Archeological Science 31 (2004): 835–853. WROE S., FIELD J., FULLAGAR R., JERMIIN L.S. “Megafaunal extinction in the late Quaternary and the global overkill hypothesis.” Alcheringa 28 (2004): 291-331. Read More