The Sixth Great Extinction

Lonesome George is a large, mud-loving Pinta tortoise (Geochelone elephantopus abingdoni) who died on the Galapagos Islands in June 2012. More than 40 years ago, George was found alone on Pinta Island and taken to the Charles Darwin Research Station, where scientists theorized that he was the last of his subspecies on the planet. A global search ensued to find a mate for George, and researchers offered a $10,000 reward to any zoo that possessed a female Pinta tortoise for the breeding program. Unfortunately, none had ever been taken into captivity. When no match was found,

the reserve tried unsuccessfully to breed George with similar subspecies in order to preserve some of his genetic lineage. George now provides a tangible and current example of extinction.

George is not the only species currently on the verge of extinction. We are in the midst of the Sixth Great Extinction, characterized by the loss of between 17,000 and 100,000 species each year. The current species extermination rate is at least one hundred times faster than the background rate, or the speed at which species were lost in the period before Homo sapiens began their migration around the planet. During this period, ten to one hundred species became extinct each year (Wilson 2010, Eldredge 2001, Leakey and Lewin 1996, Soule 2009). A recent review of known species catalogued in the World Conservation Union's Red List found 47,677 threatened species and 17,291 species in serious risk of extinction (BBC 2010). The current biodiversity crisis has the potential to become catastrophic for the human species in regard to our health, our culture and our survival on this planet.

The Six Great Extinctions on Planet Earth
The six major extinction events chronicled in Earth's geologic history have occurred over the past 450 million years and typically span periods of tens of thousands of years. Each of these events is named for the geological period, or span of time, during which it occurred. Many extinction events mark the beginning and end of two separate geological periods and take both names accordingly. During each extinction event, between 50 and 95 percent of the planet's life has been lost, resulting in dramatically changed biotic characteristics. Generally, ten million years pass before biodiversity reaches pre-event levels.

The first extinction, named the Ordovician-Silurian extinction, occurred around 440 million years ago (m.y.a.). Fifty-seven percent of terrestrial and marine genera, or groups of species, disappeared. Scientists hypothesize that both a southerly continental drift that led to a drastic decrease in temperatures and radiation caused by the collapse of a massive star known as a hyper nova may have caused these extinctions.

The second extinction was the Late Devonian. Approximately 370 m.y.a., 50 percent of all genera, including 70 percent of marine species, disappeared, causing a sharp decrease in marine reef biodiversity. Many factors may have played a part in the Late Devonian extinction, but the causes remain mostly unknown.

Around 245 million years ago, during the Permian-Triassic extinction event, an estimated 80 to 95 percent of marine species became extinct. As a result, oceanic reefs did not exist anywhere on the planet for ten million years. A combination of factors, including volcanic eruptions, climate change and a possible meteorite impact made this the largest historical extinction event.

In the Triassic-Jurassic extinction, circa 210 m.y.a., 48 percent of genera vanished from the earth, including 80 percent of quadrupeds and half of all marine invertebrates. Although the causes of this event are unknown, scientists believe that volcanic activity contributed to extinctions.

The Cretaceous-Paleogene extinction event, circa 65 m.y.a. (formerly known as the Cretaceous-Tertiary or K-T) is best known for the extinction of the dinosaurs and nearly all large animal species. Fifty percent of all genera disappeared when a meteorite collided with Earth and led to dramatic climate change. During this extinction event, temperatures increased by as much as 57 degrees Fahrenheit (32 degrees Celsius) and sea levels rose as much as three hundred meters.

We are currently experiencing the Sixth Great Extinction. Also known as the Holocene extinction, the Sixth Great Extinction is unique in its origins because it is driven almost exclusively by human actions. Based on a system that ranks extinction events based on the number of species lost and the duration of the event, the current extinction event could likely be the worst in history. It is likely that we will lose half of all plants, animals and birds on our planet by the year 2100 (Celâl Sengör et al.2008, Eldredge 2000, (Whitty 2010). Human impact on the ecology of our planet has been so extensive that chemist and Nobel Prize winner Paul Crutzen suggested that we change the name of the current epoch to the Anthropocene, emphasizing the immense and permanent impact that humans have on genes, species, and ecosystems as a whole.

The beginning of the Sixth Great Extinction coincided with the global dispersion of Homo sapiens approximately 100,000 years ago. Three theories, often referred to as kills, chills and ills, postulate what commenced the current extinction event. Developed by Paul Martin, the theory of over-hunting (or the kills or Blitzkrieg theory) considers the possibility that as humans arrived in new places, they took advantage of the fact that native species did not perceive humans as a threat, which enabled humans to hunt them with relative ease. Blitzkrieg refers to a German warfare tactic in which a rapid attack leaves the prey no time to react. 

The Blitzkrieg theory postulates that the beginnings of human migration, coupled with effective hunting techniques, completely eradicated many animal species in a short amount of time. Evidence of this exists in the global fossil record. Scientists estimate that early humans drove to extinction an entire family of giant turkey like birds in Polynesia, including eleven species of moas, in no more than 160 years – a blink of the eye on the geological time scale (Stevens 2000, Holdaway, R.N. and Jacomb, C. 2000). Research has also found that humans were responsible for the extinction of fifty species of large animals, or megafauna, in Australia as a result of over-hunting and habitat destruction by the use of fire (Jones 2010).

The chills, or over-chill, theory examines the possibility that climate change, not humans, initiated the Sixth Great Extinction. The premise behind the chills theory is that a rapid temperature reversal occurred, killing off many species that had recently adapted to an alternate climate. This could mean a transition from either an ice age to a hot climate or vice versa, occurring over a matter of days or thousands of years.

The ills theory could be compared with the damage caused to Native American populations when European explorers brought diseases to the New World. Colonizers of the Americas carried diseases that previously isolated indigenous peoples had no tolerance to, resulting in countless deaths. Similarly, the ills theory posits that as humans moved out of Africa 100,000 years ago, beginning the migration that would ultimately bring our species to inhabit most corners of the Earth, they may have transmitted diseases to previously unexposed non-human populations, rendering local or endemic species extinct (Eldredge 2001).

Regardless of the exact amalgamation of events, it is certain that the beginning of the Sixth Great Extinction coincided with the dispersal of humans, and that our activities have continued to remove species from the planet at an alarming rate (Eldredge 2001).

The birth of agriculture and animal husbandry 10,000 years ago initiated a second wave of species extinctions. Agriculture and animal husbandry are detrimental to biodiversity due to the alteration of landscapes necessary for the cultivation of crops and the raising of poultry and livestock (Wilson 2000). Both also provide the means for human populations to grow beyond what would be possible with naturally occurring resources. Limits on resources normally provide a ceiling for the growth of any population or species, known as an ecosystem's carrying capacity. With the advent of agriculture, humans granted themselves independence from the planet's natural carrying capacity (Eldredge 2001).

The Trend Continues
Despite conservation efforts recommended by nongovernmental organizations and the United Nations, and despite a small number of individuals living sustainably, biodiversity continues to decline at an increasingly rapid rate (CBD 2010). There are many contributing factors to the Sixth Great Extinction; destruction of habitat, introduction of alien species, and pollution claim the most species (Eldredge 2001, Leakey and Lewin 1996). Extinctions are also caused by overexploitation of species for consumption, collection and trade, agricultural monoculture, human-induced climate change, nitrogen loss in soil and oceanic acidification as a result of a warming climate, and urbanization leading to sedimentation and soil erosion.

The alterations of habitats for agriculture and resource exploitation add to the list of species claimed by the Sixth Great Extinction on a daily basis. Most areas, especially in developing countries, are not surveyed for the presence of endemic species before being cleared, making it likely that species there will be overlooked (Leakey and Lewin 1996). A unique situation occurred in Centinela, Ecuador, where scientists surveyed an isolated area of cloud forest shortly before the area was cleared for agriculture. During this clearing, ninety previously unknown species were lost (Leakey and Lewin, 1996).

Our current patterns of travel have also brought about extinctions, not by the direct exploitation of species, but by the intentional or accidental introduction of alien species into ecosystems. In Guam, for example, the accidental introduction of the brown tree snake caused the extirpation of nine bird, four reptile, and two bat species on the island (USGS 2010). In Hawaii, the arrival of humans (and a host of hitchhiking alien species) caused the extinction of 50 percent of the islands' bird species, with many more experiencing large reductions in population size. It is estimated that only eleven of the 135 original bird species in Hawaii are likely to survive into the next century (Leakey and Lewin 1996).

The industrial revolution and our continued dependence on industries such as the refinement of petroleum and coal, the mass production of food through industrial agriculture and the factory production of various commodities cause severe pollution to nearby habitats, especially freshwater ecosystems. In China, an estimated 30 percent of fish species in the Yellow River have become extinct due to production industry waste that is dumped into the river (Handwerk 2007).

Atmospheric pollution leads to global climate change, which also causes extinctions. Individuals of many species are rendered more vulnerable because they are unable to adapt rapidly enough to changing temperatures and succumb to disease or parasites. In 1980, there were 110 species of harlequin frog in Central America; since then, two-thirds of the species have disappeared from the planet. These brilliantly colored amphibians have died from a fungus called chytrid that was previously controlled by temperature fluctuations. A warming climate has resulted in more consistent temperatures through the day and night, which provides ideal conditions for the fungus to thrive in and has proved deadly for the frogs.

Our continually growing population as a species is now probably the single most influential factor in the Sixth Extinction. Growing human populations have led to increased demand for natural resources including petroleum, food, and building materials, plus the materials to assemble items such as televisions and cell phones. With a current world population of nearly seven billion people, and growing each second, our demand for natural resources, many of which require environmentally damaging practices to acquire, will continue to grow (Ehrlich and Ehrlich 1997).

Why should we care?
Countless species have gone extinct throughout history, and as many as 100,000 species will become extinct this year (Wilson 2000). Since most people probably cannot name a single recently extinct species, does it really matter to the human race whether we save biodiversity or let much of it disappear into the history books? The answer is a very strong and profound Yes. By not recognizing the importance of biodiversity, in addition to assuring the demise of most other species, we may be assuring the demise of our own human species as well. We need biodiversity.

By choosing to act in ways that negatively impact species globally, we are laying the foundation of our own extinction. All species are connected, and the loss of one creates a domino effect of negative impacts to interdependent species. Evidence of this lies in Yellowstone, where the removal of the wolf, a keystone predator, resulted in a trophic cascade of negative effects throughout the ecosystem. Trophic cascade refers to the effect that the change in population size of a top predator has on the food web, especially impacting the species on which it depends for food or shelter. Predators play an

important role in ecosystems – when they are eliminated, the species they preyed on have fewer animals controlling their population numbers, which allows their populations to grow. Wolves were exterminated from the western United States by the mid-1930s. In the following decades, scientists found that without a predator, deer, elk and moose ceased their normal migration patterns and began spending large amounts of time consuming the abundant vegetation in and around rivers and streams. The reduction of trees and other woody vegetation in these areas led to a drastic decline of beavers in the area, which in turn changed the flow of the rivers (Wolf Wars).

Which species' extinction might start the succession of events that causes our extinction? For that answer, we might look to bees. Over the past decade, there have been large fluctuations in bee populations, for reasons that scientists are still exploring. Agricultural pesticides, genetically modified crops, monoculture, radiation from cell towers, and other factors may cause hypersensitivity to disease, leading to colony collapse (Ho 2007). As many as one hundred, or one third, of the fruits and vegetables that humans consume on a daily basis depend on bees for pollination (Cox-Foster and vanEngelsdorp 2009). Some scientists hypothesize that if bee populations continue to decline at the present rate our agricultural system could be in danger of collapse (Amos 2008).

Our survival as a species ultimately rests on biodiversity. Each species plays a role in the global ecosystem, and we may not know until it is too late whether a given species was vital to our existence, but we can safely assume that we won't survive without a diversity of other species. Biodiversity creates and cleans our air and water. The Amazon rainforest is estimated to produce 20 to 25 percent of the planet's oxygen and 25 percent of our freshwater, as well as countless plants that may be cures for disease (Cox 2008, Butler 2010, Wilson 2010). Yet the rainforest is being destroyed at an alarming rate. Since

1970, 232,000 square miles of Amazon rainforest have been lost, equaling a land area twice the size of Greece. The latest available statistics showed an 11 percent increase in the rate of deforestation in the region (Monga Bay). Likewise, the United States continues to destroy its primary, or old growth, forests. From 2000 to 2005, an average of 831 square miles of primary forest was cleared in the United States each year. The Food and Agriculture Organization of the United Nations (FAO) published a report in 2005 that ranks the United States seventh in annual loss of primary forest globally (Butler 2005). We depend on biodiversity to provide us with clean air and water, medicine and food, and yet we continue to accelerate the pace of its destruction.

The human race is losing more than just natural resources. With decreasing biodiversity, we are losing parts of human culture as well, including traditions, languages and food customs. The growing science of bio-cultural diversity, pioneered by Terralingua and other organizations, examines integral links between biological and cultural diversity. Studies have found that areas rich in biodiversity also tend to have incredible cultural richness, and therefore, high levels of biological sustainability and cultural innovation (Harmon and Loh 2004).

An estimated half of the world's languages will be lost in the next one hundred years, equaling the loss of one language every two weeks. With each lost language, generations of traditional knowledge about technologies, medicines, environments and religious traditions are lost as well (Lovgren 2007). According to the National Geographic project  Enduring Voices, the loss of a language can even result in the loss of an entire culture. 

Loss of traditional ecological knowledge, or TEK, is both caused by and further contributes to the degradation of the environment. Traditional ecological knowledge often provides insights into science, medicine, agriculture, rural development, environmental protection, political empowerment, cultural identity, and defense of human rights (Zent 2010). Traditional mountain communities in India, for example, practice a philosophy of co-existence with nature, resulting in unique agricultural strategies that promote the sustainable use of their natural resources (Ramakrishnan 2005). TEK relating to biodiversity and individual species may hold important answers for our species as we confront a changing climate and new environmental challenges.

Global food traditions have incorporated a wide array of agricultural species and varieties throughout history and around the world, and agricultural biodiversity is also being destroyed in the Sixth Great Extinction. Our growing population creates pressure for increased food production. This has led to more intensive single-crop production, or monoculture. These combined factors have resulted in the loss of profound agricultural biodiversity. The FAO estimates that we have lost 75 percent of our agricultural variation during the twentieth century (Picone and Van Tassel 2002). The result of this loss in agricultural biodiversity is a potential crisis in food security, as diverse varieties and systems provide a safeguard from future threats, adversity and ecological changes (Munzara 2007). The destruction of our agricultural biodiversity could lead to a more expansive version of the Irish potato famine, which resulted in a million human deaths because of a lack of diversity in food crops. As human activity continues to change the Earth's climate, it is uncertain which characteristics will be required in our future food crops, but they may be nothing like those of the increasingly few crops we have chosen to mass produce now.

Species extinctions and biodiversity loss diminish opportunities for the discovery of new drugs and the development of biotechnology, thereby reducing our ability to control human disease. Hundreds of modern medications, including at least 25 percent of pharmaceuticals we rely on for the prevention of disease and treatment of illness originate from plant species (Chivian). Therefore, not only does our medical system rely on natural biodiversity, but also, with each unknown plant species that becomes extinct, we lose a potential cure for deadly diseases. Furthermore, research has shown that some infectious diseases may become more common with the loss of biodiversity. For example, malaria becomes more prevalent with deforestation, as the removal of forest canopy provides favorable conditions for mosquitoes that thrive in areas of full sunlight with stagnant water (Alves and Rosa 2007, Chivian 2010, Wilson 2010).

Conclusions
The 2010 Countdown to Save Biodiversity, a global effort created within the United Nations Environmental Programme (UNEP), aims to reduce the rate of biodiversity loss but has been unable to substantially change the alarming pace of species extinction. It is essential, now more than ever, that global action be taken on the level of government, organization, corporation and individual to slow the rate of biodiversity loss. In 1992, 190 countries ratified the Convention on Biological Diversity, stating their intention to reverse the rate of biodiversity loss. It is relevant that the United States, being one of the world's largest consumers of natural resources has still declined to ratify this convention as of the end of December 2010. The most recent report from the Convention on Biological Diversity, published in May 2010, states that biodiversity continues to decline in every component, indicating that genes, species and ecosystems are still disappearing at an alarming rate. The Secretary General of the United Nations warns in the report that biodiversity loss is reaching such a rapid rate of decline that it could "catastrophically reduce the capacity of ecosystems" to provide the services humans rely on for food, fresh water, health, recreation, culture and spirituality (CBD).

The world's leading scientists suggest that conservation measures, sustainable development, stabilization of the human population, and the support of environmentally responsible economic development will be essential in halting the extinction crisis (Eldredge 2001, Wilson 2010). In addition to these measures, it has been acknowledged that action requires an awareness of, and a connection to, nature (Soule 2009). [See M.Soule's interview in Izilwane]. Therefore, our first steps in averting our own extinction and beginning to conserve biodiversity are to change our cultural perceptions of the natural world and begin to value biodiversity for providing us with the materials to build our homes, and ensure our nutrition, our water and our lives, and then act to preserve that which sustains us.