Anthropogenic Mass ExtinctionHomo sapiens and the

Evolution of the Biosphere since the Pleistocene

Kyle BurchettUniversity of Kentucky

Mass Extinctions of the Past

→ Unavoidable

Prolonged Geologic Events

Cosmic Collisions

Mass extinctions are normal events for Earth’s life forms.

(Erickson 2001:78)

The Fittest of the Fittest

Microscopic organisms such as bacteria show up in the fossil record for at least four billion years.

They are virtually indestructible and immune to the mass extinction events which regularly befall more ‘complex’ species.

An Objective View of Mass Extinction

“In a sense we are like fruit flies, which live but a few weeks and cannot experience most seasonal changes, much less a year. We cannot know from experience the history of planet Earth. Most of it is destined to be as abstract to a layperson as the dimensions of the universe” (Martin 2005:54).

Approximately 50,000 years ago, the Earth’s megafauna began to exhibit an unusual extinction pattern.

Almost exclusively large animals – megafauna – rapidly began to disappear around the world.

65% of mammal genera whose members weighed more than 97 pounds were utterly extirpated.

97 of 150 genera of megafauna became extinct.

Plants and marine life were largely unaffected.

Previous mass extinctions evenly affected all types of organisms, including animals of all sizes, plants, and marine life.

(Barnosky et al. 2004; Lyons et al. 2004; Martin 2005; Nogués-Bravo et al. 2010)

The Pleistocene Puzzle

Three Compelling Hypotheses

Climate Change(Generally construed as non-anthropogenic)

OverkillAnthropogenic

HyperdiseaseAnthropogenic or otherwise

Climate Change

(Nogués-Bravo et al. 2010:2444)

Extreme climate changes radically alter the possible biotic composition of ecosystems.

(Delcourt and Delcourt 2004)

Extinction may be the only possible response for some species.

(Boulter 2002:119)

Competition for limited available resources increases drastically both within and across species.

If access points to alternate habitats are cut off, migration is not an option.

Climate change alone, however, is insufficient. . .

Climate-induced mass extinctions should not show discrimination for large body size or exclude plant and marine life.

20 glacial-interglacial periods / 2 million years A mass extinction pulse only shows up at

the end of the Pleistocene (and continues today).50% of plant and marine life are currently

threatened with extinction.

(Boulter 2002:51)

Invasion → Overkill → Extinction

b

(Martin 2005:7)

A Smoking Spear?

76 North American Clovis sites reviewed14 contained extinct megafaunal

remains12 – mammoths2 – mastodons

(Grayson and Meltzer 2002)

Mass extinction inevitable – even with moderate human population growth and

hunting practices(Alroy 2001:1895)

Buffalo Jumps

Entire herds driven over cliffs(Burroughs 2005:187)

Bone layers as deep as 20 feet

Historical mass killing of megafauna

The Passenger Pigeon

At the beginning of the 19th century, flocks stretched across North American skies for up to 500 kilometers.In less than a century, this seemingly

ineradicable species was utterly extirpated.

Modern example of overkill

Naïve species meetinvasive omnivore species

Historical and modern extinctions in isolated / island ecosystems

(Boyer 2008; Martin 2005)

Overkill alone is likewise insufficient. . .

Extinctions prior to invasion of Homo sapiens

Long duration of coexistenceLoss of

naïveté

(Hofreiter and Stewart 2009:R589)

Europe and Northern Asia

Hyperdisease

113 North American mastodon skeletons / various geographic regions 52% exhibited signs of tuberculosis

(Rothschild and Laub 2006) Infection evident 34,000 – 10,000 years BP

Populations greatly weakenedMore susceptible to climate change / overkill

(Rothschild and Laub 2006:562)

Historical validation

1st recorded extinction by infection in a free-ranging wildlife species

Sharp-snouted day frog

1 other historical case of extinction by infection (in a remnant captive population)

Polynesian tree snail(Schloegel et al. 2006)

European introduction of

diseases such as measles and smallpox reduced Native American populations by perhaps as much as 95 percent (Dobyns 1993).

Hyperdisease alone insufficient. . .

20 glacial-interglacial periods / 2 million years

Many opportunities for novel pathogen introductionoMass extinctions only occur near the

end of the Pleistocene and only in large land animalsNo known analogous pathogens (such as

West Nile virus) demonstrate such size selectivity

(Lyons et al. 2004b)

A multicausal approach

Climate Change + Infection + Keystone Invasive Species = Mass Extinction Event

with Homo sapiens tipping the scale. . .

Homo sapiens

. . . an invasive specieswith life-negating metaphysical beliefs about.

. .

The inexhaustibility of natural resources

Homo sapiens as quasi-divine

fundamentally separable from all other life forms that have ever existed on the Earth

with little regard for the consequences

Entitled to:

Consume

Commoditize

Invade

Occupy Exploi

t

Exterminate

Behold the Rational Animal. . . .

Man has been educated by his errors: first, he saw himself only incompletely; secondly, he endowed himself with fictitious attributes; thirdly, he placed himself in a false rank order in relation to animals and nature; fourthly, he invented ever new tables of goods and for a time took them to be eternal and unconditioned . . . .

Nietzsche, GS 115 (1882)

Current Extinctions

(Gorke 2003:1)

One species every 20 minutes.

This rate is more than one thousandfold greater than the natural background rate (Pimm et al. 1995, Wilson 1992).

Even though human-induced species extinction presently seems to rank low on people’s attention scale compared to other political and societal topics, this does not mean that its significance in earth history or its ecological consequences have diminished in any way. It must repeatedly be made clear that if current trends continue, within the next one hundred years half of all our planet’s species will most likely have become extinct. Thus, members of today’s generation are witnesses and also perpetrators of the greatest catastrophe in the history of life since the disappearance of the dinosaurs 65 million years ago.

- Martin Gorke, 2003

http://www.digitalsurvivors.com/archives/worldpopulation.php

Nonhuman megafauna’s loss of habitat and access to migratory

routes

due to Homo sapiens’ expanding invasion of ‘novel’ ecosystems

Amazon deforestation in the state of Rondônia in western Brazil, 07.30.2000

Amazon deforestation in the state of Rondônia in western Brazil, 08.21.2009

The fragmentation of natural habitats essentially creates isolated ‘islands’ where species’ vulnerability to extinction is heightened as the ecosystem processes and services they depend on for survival are disrupted by biodiversity reduction, competition with invasive species over a shrinking resource base, pathogen dispersal, pollution, and numerous other anthropogenic factors.

The megafauna du jour

Consumption patterns of industrialized nations are not ideals for which the ‘developing’ world should strive.

based on short-term ‘profit’ and convenience for a ‘wealthy’ minority

ignore effects on biodiversity and the long-term survivability of megafaunal species such as our own

Over-consumption of toxic and limited resources

If India alone adopted the consumption pattern typical in the US, the global ecological impact would be as if the world’s population had doubled to 13.2 billion (Cox 2008:114).

The inexhaustibility of natural resources. . .

. . . a false (and ultimately life-negating) premise.

Hubris today characterizes our whole attitude towards nature, our rape of nature with the help of machines and the completely unscrupulous inventiveness of technicians and engineers.

- Friedrich Nietzsche, GM (1887)

Ecosystems eventually ‘bounce back’. . .

. . . but not always on an anthropocentric timescale.

It usually takes 10 million years for Earth’s multicellular biodiversity to ‘return’ to pre-mass-extinction levels. It took 100 million years after the end-Permian event (Benton 2003:155).

The duration of Homo sapiens’ tenure depends on future consumption practices.

Homo sapiens is part of the natural world and is just as susceptible to extinction as Earth’s other organic beings.

The X Factor

Earth is becoming less biodiverse as a result of the escalating global invasion and consumption practices of Homo sapiens.

What kind of biosphere are we creating? Will it support the continued existence of organisms such as ourselves?

The dreams of science fiction will not save our species from

extinction.

There is only one Earth.

Blessed are the meek. . .?

The Post-Human Earth

It’s a small world, after all. . . .