Late Pleistocene Extinction
Within their study, scientists have long discovered that to understand present life forms there is a significant need to comprehend life in the past. There are more to study about life than just observing the living. Life started millions of years ago, and trough artifacts and fossils we have learned that there are unlimited numbers of species that have once lived and extinct above our planet. One of the most popular discussions of the subject is the Megafauna. It is popular for several reasons. First, it is popular because of the magnificence to have animals with that structure and size living relatively close to our lifetime (about 10 to 15 thousand years ago). Many of the discovered artifacts and fossils are in good and preferable conditions for empirical studies. Second, it is popular because of its mysterious disappearance within the late Pleistocene epoch.
For decades, scientists have tried to unravel the mystery of life’s birth and extinction. Most of the study ended up with endless debates and with various contradictions of empirical evidences. Even Darwin’s theory of evolution is now being protested because of new discoveries and logical reasoning that enlarge the logical gaps within the theory. Similar debates and logical contradiction of empirical evidence are what also happened within discussion of the late Pleistocene extinction. There are various theories developing within the science community. Each is holding on to their own ‘indisputable’ evidences or logic. New and more empirical studies are still being performed in the purpose of resulting a conclusive theory to explain the Megafauna Extinction.
Within this short elaboration, we will describe the strongest theories that have attempted to explain the Late Pleistocene Extinction. For the very least, this literature review would describe the current condition of the debate and could be use as a logical basic for further theoretical development.
II. Late Pleistocene Extinction
II.1 Stages of Time
In the field of geology, scientists have divided the planet into stages of time. To properly understand where exactly the event occurred in the past, it is better to shortly elaborate this subject. According to the geological science, time on earth is divided into two large stages:
Ø The Precambrian Eon, which started about 4,600 million years and ended about 500 million years ago
Ø The Phanerozoic Eon, which consist of 500 million years of time since the end of the Precambrian eon until today.
(Geological Time-Scale, 1996)
There is so little that we know about the Precambrian Eon due to unavailability of our scientific method to draw empirical conclusions from such a distant time. Thus, scientific study of the planet is more popular within the Phanerozoic Eon. The Phanerozoic eon is divided into shorter periods. Era is a period consists of hundreds of millions of years. Period is a period consists of aversely 20 or 30 millions of years. Epoch consists of 1 to 10 millions of years. The most recent epoch is the Holocene epoch (<10 thousand years), followed by the Pleistocene epoch (Geolocical Time-Scale, 1996).
The Pleistocene epoch was a period started about 1.8 million and ended approximately 10,000 years ago. The modern continents were mostly at their present positions during the Pleistocene epoch, possibility of continents shift is no more than 100 km from the present position. The Pleistocene Climate was marked by repeated glacial cycles. Each Glacial cycle could result a temporary drop of sea level of 100 meters or more. The Pleistocene biotas were extremely similar to modern ones. Many of them even survived until today Scientists also believed that prehistoric man evolved into modern man during the Pleistocene epoch (‘The Pleistocene’, n.d).
II.2 Megafauna Extinction
During the last 50 thousand years, many important events lead to the mass extinction of existing animals. But according to available researches, this extinction did not occur with the same manner across different Genera (a group of related species). It was much more selective, involving mainly the Megafauna. By definition, Megafauna are the large animals of any particular region or time (Megafauna, 2005). However, within this literature review, we are referring to Pleistocene Megafauna, which lived over 10 thousand years ago in the late Pleistocene epoch. The following disappeared from America, Europe and Australia:
Ø All herbivores above the weight of 1000 kg
Ø 75 % of herbivores between the weight of 100 and 1000 kg
Ø 41 % of herbivores between the weight of 5 and 100 kg
Ø 2 % of herbivores under the weight of 5 kg
The Pleistocene Megafauna divided by region are:
v American Pleistocene Megafauna
Large mammals of the area include Giant Sloths, the American Lion, Cheetahs, Saber-toothed Cats, Dire Wolves, Camels, Wide-horned Bison, Horses, Woolly Rinocheri, Mammoths, Mastodons, Giant Beavers and Giant Condors (‘Pleistocene Megafauna’, 2005).
v Australian Pleistocene Megafauna
There are several similarities of today’s Australian megafauna with those of ancient ones. Pleistocene Australia are characterized by Marsupials and Monotremes, Carnivorous Kangaroos, Diptrodon, Giant Wombat, the Marsupial Lion, 3 meter flightless bird Dromonis, 5 meter snake Wonambi, and the Giant Lizard Megalania (‘Pleistocene Megafauna’, 2005).
v Eurasian Pleistocene Megafauna
Some elements of North America could be found in Eurasia. Eurasian Pleistocene Megafauna include the Woolly Mammoth, Cave Lion, Cave Bears, Irish Elk and Eurasian Rhinoceros (‘Pleistocene Megafauna’, 2005).
v Pleistocene Megaphone of other Regions
There are several recorded fossils of Megafauna that exist in several other areas which are:
Ø the Moas and Harpagonis (Giant Eagle) in New Zealand
Ø the Gorilla-sized Lemurs and two species of Hippopotamus on Madagascar;
Ø the Giant Birds, Land Turtles and Crocodiles on New Caledonia
Ø the Giant Geese and Moa-nalos (Giant Ducks) in Hawaii.
(‘Pleistocene Megafauna’, 2005).
The major extinction episodes also happened in different times for different land masses:
Ø For Africa, Asia and Australia it started 50 thousand years before the present
Ø For North Eurasia, 13 thousand years
Ø For North America, 11 thousand years
Ø For South America, 10 thousand years
Ø In West Indies, 4 thousand years
Ø In New Zealand , 900 years
Ø In Madagaskar, 800 years
Scientists have been observing existing evidences and artifacts for more than three decades and have not yet agreed on what caused the mass extinction episodes. However, there are 2 theories which hold the strongest arguments until today. They are the Climate theory and the Overkill theory.
III. Overkill Theory
Mankind has dominated this planet for thousands of years. In any ecosystem, the superior animals are known to develop a certain balance with their nature, while humans tend to ‘govern’. This might be the largest difference between humans and animals. This unique nature of human behavior is also supported by their physical structure (having a free use of their hands and a larger brain capacity, which enhanced learning capabilities). Possessing those advantages, humans are practically ‘given’ the ability to take advantage of nature and animals for personal survival or development.
Paul Martin from the University of Arizona believes that humans were responsible for the extinction of the Megafauna at the end of the Ice Age 10 thousand years ago. This theory has received many justifications from other writers using different evidences and logical argument.
The strongest logic of this theory relates to timing. As we have elaborated above, different regions experienced mass extinction of Megafauna on different times. According to several researches, in every region except Africa, Pleistocene Megafauna started to disappear shortly after the arrival of prehistoric man. Within those times, prehistoric humans have evolved to be very skillful hunters. They are also nomadic and expansionist in nature. Several scientists argued that prehistoric humans arrived in new environments as the most aggressive predators of the time. Relating to the fact that the Megafauna are the largest and slowest mammals in the environment, it is very logical to conclude that large animals of the Pleistocene epoch become extinct because of over exploitation by human ancestors (Bryant, 2002).
As for Africa, scientist believed that expansionist tribes did not ‘come’ to Africa. African people are natives evolving along with their animals. The slow evolution of African human from scavengers to skilled hunters has given the ecosystem (including the Megafauna) time to adjust. While in other regions, human arrived as already skilled hunter, shocking the ecosystem by its intensely frequent hunting activities (Bryant, 2002).
IV. Climate Theory
The other major theory comes from Donald Grayson, an Anthropology Professor. Grayson argued that climate shifts is the most valid cause of Pleistocene Megafauna extinction. During the Pleistocene Epoch, which ended about 10 thousand years ago, there were subsequent changes in weather that were most likely to effect every existing life form on the planet. The massive ice sheets that covered much of the Northern Hemisphere began retreating. In North America, the previously thick icy mantle prevented the Artic weather system from entering the mid continent. With the absence of the icy mantle, the climate became more similar to today’s, marked by cold winter and warm summer (‘Blame’, 2001).
Large animals with tick layer of fat and furs might not be directly affected by the climate change, but vulnerable plants did. There were massive reorganizations of biotic communities (‘Blame’, 2001). Many of the large animals are herbivores. The change of biotic environment resulted stressful change of diet, which for some herbivores, have seemed to be an unbearable transition. Russel Graham, a Paleontologist with the Denver Museum, discovered new data, which shows that small mammals were also became locally extinct at the same time. The change of plant diet for large herbivores and the extinction of small animals (which include the diet of large carnivores), resulted the extinction of some 35 genera of North American mammals (including Horses, Camels, Bears, Giant Sloths, Saber-toothed Cats, Mastodons and Mammoths) (Blame, 2001).
V. Plague Theory
Hyper-disease Hypothesis is one of the minor theories which attempted to explain the Late Pleistocene extinction. This theory was stated by Ross Mcphee, a curator of vertebrate zoology at New York’s American Museum of Natural History. He believes that human hunting and natural climate change themselves would not be enough to cause such elevated death rate among Pleistocene Megafauna. He is betting that viruses arrived along with the by human hunters are the ones who killed many large mammals which have no natural resistance. He stated that the evidence came afterwards, as the native Americans are devastated by smallpox, measles and other ‘European’ infections (Okie, 2001).
The three theories stated above have been the strongest arguments of the subject. However, there are strong and weak spots in all of them. The overkill theory for example, has now become more of a faith-based policy statement that bows down to green politics. It argued that the Megafauna would still be around if people had not kill them. The overkill theory fits the image of mankind as the powerful ruler which crime could be disastrous for life, as would be agreed by the perspective of Judeo-Christians. The theory lacked empirical evidences. The only solid evidence of Megafauna killings that were associated to man is the Mammoths.
The overkill theory has also stated that Megafauna killings in North America were associated to the arrival of the Clovis people 11,000 years ago. However, there are evidences that show human expansion to North America as far back as 33,000 years before the present, and the supporters of overkill theory has seem to ignore this fact. Evidences also show that the assumption of Megafauna’s mass extinction happened 11,000 years ago was seriously doubted. No more than 15 genera can be shown to have survived beyond 12,000 years ago. So the extinction mentioned in the overkill theory, could only be associated to the extinction of no more than 15 genera. Scientists also often mentioned their doubts that human colonization, without the help of no other factors, could be responsible for the death of so many large animals living on so extensive areas. We have certainly witness how human expansion to isolated islands caused extinction for some species of those islands, but how could human expansion caused extinction of hundreds of large species within many continents? (‘Blame’, 2001)
Toward the statement that only 15 genera had survived beyond 12,000 ago, Paul Martin responded that Pleistocene Megaphone had survived several climatic changes over the previous million years. Some were more severe than those of the late Pleistocene. However, non have resulted mass extinction as what happened in the late Pleistocene. The supporters of the overkill theory also stated that besides hunting for food, prehistoric humans have also hunted for fur (Bryant, 2002). Relating to the fact that the Pleistocene Megafauna are large animals of the Ice age, the hunt for fur will put them on the top of the hunting list target for prehistoric man. This would significantly increase the rate of Megafauna hunting all over the North American continent.
The climate theory has also discovered to have some weak links. The largest gap within the theory is the fact that global climate change happened within limited period, while Megaphone Extinction happened within different times for different landmasses. If the change of climate was the reason of the mass extinction, than its should happen on every continent at the same time. The fact that it did not, pose as a weak spot for the climate theory.
The research of isotopic ecology of Late Pleistocene mammals in North America has discovered many of those large Animals have specialized diets. This leads to the conclusion that the dietary change caused by the climate change resulted dietary stress toward many of the Pleistocene Megafauna. The statement supported the Climate theory. However, there are no empirical evidences that the dietary stress were adequate to cause extinction or even deaths. Other supporting evidence is the opinions that the amount of Pleistocene Megafauna has decreased significantly before it finally disappeared 11,000 years ago.
The Hyper-disease Hypothesis has also came in to the debate as they argued that Pleistocene Megafauna had survived many climate change in previous decades. Thus, there is no reason to believe that The Megafauna would fail to survive the Late Pleistocene. The supporter of the theory stated that the cause of extinction had to be human or parasites of human. This is logical because a new infection would have spread quickly among animals of all ages and sexes and able to cross species barriers since local animals would not yet develop natural resistance. Ross McPhee stated that the possible virus is the kind that spread trough the air such as influenza and rinderpest, a disease of cattle that also affects deer, antelope and related species (Okie, 2001).
Several scientists and students believe that the existing factors have all contribute in the process of Pleistocene Megafauna extinction. They argued that singular theories are only acceptable within limited scope and non-could have been single handedly responsible for the extinction of the entire Pleistocene Megaphone.
VII. Conclusion 1
In the search of causes of Megafauna Extinction, scientists have resulted several empirically and logically valid theories. However, there is still no conclusive statement that ended the debate which has lasted for more than three decades. The strongest theory is still the overkill theory, which placed the humans responsible for the case. However, the amount of doubt and logical gaps of the theory are almost as famous as the statement of the theory itself. Other theories like the climate-change theory and the plague theory have also not yet freed from logical gaps. As supporters of each theory strive to find more evidences for a conclusive statement, general opinion have started to form their own conclusive statement. Many believe that the three theories mentioned above are all contributed to some extent, to the cause of Pleistocene Megaphone extinction. There is a popular saying that the Pleistocene Megafauna were extinct because of three things, kill, chill and ill.
‘Blame North America Megafauna Extinction on Climate Change, Not Human Ancestor’. 2001. EurekAlert. Retrieved July 15, 2005. Available at http://www.eurekalert.org/pub_releases/2001-10/uow-bna102401.php
Bryant, Peter J. 2002. ‘Biodiversity and Conservation’. Retrieved July 15, 2005. Available at http://darwin.bio.uci.edu/~sustain/bio65/lec03/b65lec03.htm
‘Geological Time-Scale’. 1996. Geology and Geophisics. Retrieved July 15, 2005. Available at http://www.geo.ucalgary.ca/~macrae/timescale/timescale.html
Okie, Susan. 2001. ‘Megafauna Extinction Mystery’. The Japan Times. Retrieved July 15, 2005. Available at http://www.trussel.com/prehist/news275.htm
‘Pleistocene Megafauna’. 2005. Wikipedia. Retrieved July 15, 2005. Available at http://en.wikipedia.org/wiki/Pleistocene_megafauna
‘The Pleistocene’, n.d. Paleontology Institute of Rusia. Retrieved July, 15, 2005. Available at http://darwin.bio.uci.edu/~sustain/bio65/lec03/b65lec03.htm