Introduction
The Pleistocene era, or the last ice age, lasted from around 2.6 million to about 11,700 years ago. The prolonged period saw many changes to flora and fauna of the planet, with the Homo sapiens evolving for the first time around 200,000 years ago. Furthermore, the movement of the plate tectonics resulted in the geographic structure of the Earth as it is today. However, one of the most prominent debates that remain today is on the causes of the global mass extinctions of large mammals in the late-Pleistocene period.
Possible Causes of the Extinctions
As mentioned above, there are various debated explanations for the mass extinctions of large mammals in the Pleistocene era. Although North America is generally considered as the area most affected, other areas such as Australia, Europe, Asia, and South America were affected as well. With the arrival of the Homo sapiens in the latter part of the period, it is unsurprising that some scientists attribute the megafauna extinctions to excessive human hunting. Another major theory is that climate change was responsible for the mass vanishings of animals. Lastly, the least popular and yet also probable argument is that of the rapid spread of disease as the main reason behind these extinctions. Although the extinctions likely occurred as a result of a combination of all of the above reasons, this paper maintains the view that climate change was the most prominent cause.
Human Hunting
Although today there are numerous movements, from PETA to individuals following the vegan diet, that strive to protect animals from being killed for consumption, historically, this was not the case. Homo sapiens of the Pleistocene period were not an exception. Hunting was a primary source of nutrients for thousands of the human species for hundreds of thousands of years, which inevitably led to a decrease in the population of certain mammals and other animals. According to van der Kaars et al. (2017), evidence was found of human consumption of the eggs of the now-extinct bird Genyornis newton. Considering that Genyornis newton went extinct around the same time that humans appeared in Australia, the homeland of the giant bird, proves that humans had a significant impact on the extinctions.
Furthermore, van der Kaars et al. (2017) state that the mass extinction of the megafauna, both mammals and other large animals, happened around 2000 years after the human dispersion. Moreover, according to the findings of Broughton and Weitzel (2018), there is a correlation between the increase in the human population in North America and the decrease in megafauna population. The study explicitly links the decline in the mammoth, horse, and saber-tooth tiger populations with human hunting activities (Broughton & Weitzel, 2018). Therefore, it is obvious that the effect that humans had on the decline and eventual extinction of the megafauna during the Pleistocene period is not trivial.
Climate Change
Another major theory, as mentioned previously, is that of climate change as the main cause of the mass extinction of mammals during the Pleistocene period. The Pleistocene era is also referred to as the last ice age, meaning harsh temperatures, as well as extreme changes in the weather conditions. According to Broughton and Weitzel (2018), data from some areas in North America, such as the Great Lakes, are consistent with climate change as the main cause for the extinction of mammals. Furthermore, large animals that were hunted by humans were unable to migrate far enough to escape the severity of the climate change, hence decreasing their chances of survival. The ecological changes, such as fires, landscape changes, floods and droughts, and severe cold, were harsh conditions for the animals. Since North America was most affected by the extinctions, a lot of the studies tend to focus on the continent. However, the rest of the world also experienced mass extinctions, and it is difficult to isolate a single geographical location.
Spread of Disease
Lastly, the least popular and yet recently more acknowledged theory is that of disease as the main cause of the mass extinctions in the Pleistocene era. According to Nickell and Moran (2017), there are a number of diseases that were brought into the ecosystem of North America by Aboriginal humans that could have assisted the mass extinctions. Some of these diseases include Tuberculosis, Anthrax, and Pertussis (Nickell & Moran, 2017), and their appearance on the continent happened at the same time as the human colonization. Although there are numerous other diseases and viruses that were brought by humans, it is not necessary to go into detail and list all of them to understand the extent of the impact. This theory is further strengthened by the fact that hunting was not confirmed for most of the megafauna, and archaeological evidence suggests that hunting was not widespread enough to cause mass extinctions (Nickell & Moran, 2017). These reasons prove that more studies should be done on the topic of disease spreading as the cause of the mass extinctions. Although this would then prove that humans were not directly responsible for the extinctions, it would still make them indirectly responsible, as they were the ones that brought the diseases from Eurasia.
Climate Change as the Main Cause
As mentioned above, climate change was the underlying reason for the mass extinctions. Although all of the reasons were significant, it was climate change that ultimately made survival impossible for some species during the Pleistocene period. Nevertheless, the importance of the contributions of the other factors cannot be overlooked. If it was not for human hunting and the spreading of the disease, the animals would be more likely to migrate and adapt to the weather changes and hence would not experience the mass extinctions that they have experienced. Climate change, which caused thousands and millions of animals to be unable to reproduce and to shield and nurture their offspring, left them no way to survive. Furthermore, since the evolution of animals happens very slowly, and human hunting did not give the animals the time to evolve, they were not able to change for survival.
Conclusion
In conclusion, as mentioned above, it was the combination of factors that caused the extinction of mammals during the Pleistocene era, with climate change being the most prominent one. It is difficult to distinguish the consequences of the separate factors. However, it is possible that without climate change, mammals would learn to coexist with humans, who would become a part of the ecosystem. However, climate change weakened the defenses of the large mammals, giving an advantage to Homo sapiens and animals that were more capable of migrations. Although it is still not completely clear what the cause was, and it is possible that in the future new causes will be found, this conclusion should serve as a warning to the Homo sapiens of today. It is important to understand the impact of a combination of factors, including the human hunting and consumption of animals, as well as the human impact on climate change. Regardless of the extent of the human impact, it is undoubtedly significant, and as can be seen from history, it might lead to mass extinctions in flora and fauna.
References
Broughton, J.M. & Weitzel, E.M. (2018). Population reconstructions for humans and megafauna suggest mixed causes for North American Pleistocene extinctions. Nature Communications, 9(5441).
Nickell, Z. D. & Moran, M. D. (2017). Disease Introduction by Aboriginal Humans in North America and the Pleistocene Extinction. Journal of Ecological Anthropology, 19(1), 29-41.
van der Kaars, S., Miller, G., Turney, C., Cook, E. J., Nürnberg, D., Schönfield, J., Kershaw, A. P. & Lehman, S. J. (2017). Humans rather than climate the primary cause of Pleistocene megafaunal extinction in Australia. Nature Communications, 8(14142).