The long history of the Earth has been remarkably varied. The fossil records show 5 great periods on mass extinction of species. In one episode 90% of all species disappeared. We now are hearing that we are into the 6th great extinction. The evidence seem to point to that statement as being valid.

Do hunters cause extinction?

Extinction blamed on human's appetite.

For more than a century scientists have been debating what killed off the big animals in Australia and the Americas. Now, two studies blame ancient hunters equipped with fire, spears and an appetite for meat.

The studies, appearing in the June 8th journal Science, conclude that after early humans migrated into Australia and The Americas, the heavyweight animals of these new continents were driven to extinction within a few thousand years.

In the Americas, 73 percent of large plant-eaters, along with the saber tooth cat, were gone within 1,200 years after humans migrated to the continent about 13, 600 years ago. Wiped out were animals like mammoths, camels, mastodons, large ground sloths and the glyptodont, a strange armored creature the size of a small car weighing more than 1,400 pounds.

In Australia, researchers precisely dated bone specimens of elephant size marsupials, giant snakes, huge lizards and other extinct animals. They found that the wildlife disappeared within 10,000 years after humans arrived at the down-under continent.

The research contributed powerful new evidence to a centuries old debate among scientists intrigued by the question: What killed off the big animals on newly settled continents in the new World?

Some have long blamed humans, but other exerts say it could have been climate change, disease and gradual change in habitat.

The two new studies pin the blame squarely on humans.

"Human population growth and hunting almost invariably leads to major mass extinction", said John Alroy of the University of California, Santa Barbara, author of the study off American Extinctions.

Linda Ayliffe of the University of Utah, Salt Lake City said precise dating of rocks and fossils from 27 sites in Australia and West Papua New Guinea clearly show that large animals there disappeared around 46,000 years ago, or about 10,000 years or so after the arrival of humans.

The rapid demise during that time of 55 species-every land animal, reptile and bird in Australia weighing more than 220 pounds- is strong evidence for human involvement in the extinction, said Ayliffe.

" It is clear that the downward spiral of these animals was after the arrival of humans ", she said.

Ayliffe said the dating is significant because some researchers have blamed the extinction on extended droughts that occurred later. But she noted that the animals had withstood climate changes previously; so it is unlikely they all would have succumbed to natural forces. Also, disease is improbable since so many different species of reptiles, birds and mammals disappeared at about the same time. Diseases are unlikely to affect all species the same way.

Ayliffe said it is unlikely that hunting alone led to the disappearance of so many large animals. She said there is evidence that humans 55,000 years ago used fire as a hunting tool, burning vast areas of Australia.

Such fires would change the habitat, which would make it difficult for large animals that require
plenty of forage to survive, she said.

Tyler R. T.

I think someone on another post got it right, we must make up the rules and abide by them. Our rules are meant to prevent us from making a species extinct, and, actually, I think those who follow the rules actually contribute to the thriving of the target species via financial support and public awareness.

That being said, we have also proven beyond a doubt that collectively we have the unquestioned ability to eliminate any and all animal species, save for rats, mosquitos, and potato bettles. We do this by overhunting, over harvesting, and habitat destruction. No animal is sport if we don't follow the rules we set for ourselves.

Back then the concept of extinction was likely foreign, the rules made to maximize success. I think it possible that we may have done in some marginal species under those conditions, even in our primitive state.

Wes

[This message has been edited by Wes (edited 06-17-2001).]

"DO HUNTERS CAUSE EXTINCTION?"

NO! not sport hunting! Market hunting, done unchecked, will cause extinction, and that is what these studies are eludeing to. The mass killing of any species for food, skins for clothing, and houseing, and bones for the makeing of tools will definetely cause a reduction in the TARGET species. I say TARGET species, because that is what MARKET HUNTING is all about, the TARGETING of the easiest animal to take, with the smallest amount of risk, yealding the most product, is targeting, without limits!

Considering the people involved in these two studies, and the locations of the schools, and considering the attitudes that prevade these schools, it is my belief that there is a hidden ajenda here trying to connect Modern regulated hunting with extinction, in the minds of the ignorant! Nothing could be farther from the truth! In fact, if it were not for regulated renewable resourse conservation, by the hunting comunity, and Game depts, many of the species that were faced with extinction at the turn of the century, caused by UNREGULATED MARKET HUNTING, would be gone from the earth today.

The above is not from any study, but from my own 64 years of experience in the game fields of the world. To quote Capstick, "where there is no hunting, there is no game, not the other way around"

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..Mac >>>===(x)===>

I agree very much with MacD37.
However I wonder if also a disease could have been transited to which no natural defense was present?
Or a predator or spices which the resident species had no defense or food competition?

Hello William

Our ancestors did it, from the evidence. We are engaged in doing it to oceanic species as we write these posts. The Grand Banks had to be closed because we got too good at finding fish and not good enough at counting them before we took them out of the water. It is not the only resource in trouble.

We are also becoming victims of our own success in the area of habitat reduction; we are in the process of finding the human carrying capacity of various parcels of land as we reproduce ourselves too well. Many decent places to live will be destroyed in the next century, and wars will result from the displaced populations struggling to find new places to wreck.

Tom

I remember reading about these reports a couple of months ago and my first thought was "there's more liberal hogwash masquerading as science". The authors of the report don't give any evidence of links between the extinction of the large animals in north america with the arrival of man. Trying to tie the two together without evidence is the same as offering as proof that my arrival in the world in 1968 was responsible for the vast expansion in computer technology that happened twenty years later. Just because man arrived on the continent and certain animals became extinct a couple thousand years later doesn't mean man caused it. The overall tone of the report should be enough to establish it as typical liberal blather.

Several points refute their premises. 1) There have been several sites unearthed recently that place the arrival of humans on the north american continent at around 20,000 B.C., not the 13,600 years ago mentioned in the report. 2) 13,600 years ago we were at the end of an ice age, a gigantic climatic change which could certainly account for mass extinctions. 3) The number of humans that migrated from asia to north america would have to have been a tiny number, certainly not enough to wipe out all the large animals on the continent.

There are many so called "scientists" in this day and age that have an social agenda and are more than willing to offer their "professional" opinion in support of a fradulant claim. Look at all the kooks that came out of the woodwork to testify O.J. Simpson couldn't have committed those murders when DNA evidence proved that he did it. Unfortunately we live in an age where a supposedly expert scientist's opinion has to be read through the bullshit filter to be believed.

The death of the dinosaurs wasn�t unique. There have been 17 major extinctions of life during the past 600 million years. And, in most cases, an asteroid probably wasn�t to blame. The answer may lie in great volcanic eruptions.

Extinction has always been a controversial subject. Even after decades of intense study, researchers are still arguing over the cause of the best-known mass extinction, the �death of the dinosaurs.� And there�s a topical slant in the idea that - even today - species are regarded as "endangered" if they are relatively susceptible to extinction. Then too, what thinking person could have avoided wondering whether our own species is slated for extinction and, if so, how long we have before we meet our fate?

The disappearing Mammoth

Two centuries ago extinction held centre-stage in an even more fundamental debate: whether the Bible should be interpreted literally. The bones of a very large fossil elephant (a �Mammoth�) had been collected in the then new world of North America. Discussing the Mammoth at the National Institute of Sciences and Arts in Paris in 1796, the French anatomist Baron Georges Cuvier argued that the bones belonged to a unique species of which no living examples were known. It was extremely unlikely that such a large animal could have gone undetected if its descendants had survived to the present day, so Cuvier pronounced the species extinct.

This conclusion contradicted religious dogma of the time. A benevolent creator, it was assumed, would not allow any of his creation to disappear from the Earth. In this way, Cuvier fired off one of the first salvos in a debate between theologians and natural historians that culminated 60 years later with the writings of Charles Darwin - and still continues in some quarters of society to this day.

Observing extinctions

Since Cuvier's time, extinctions have studied primarily by palaeontologists - scientists who investigate the remains of ancient life. For all that is said in popular books, articles and television programmes, the study of extinction is a surprisingly problematic and young field of inquiry. Extinction is one of the most common observations in palaeontology, but it remains very difficult to understand precisely why a particular ancient plant or animal species went extinct.

Much of this difficulty stems from the way that scientists �observe� an extinction. Stated rather badly, we study extinction by observing what isn�t there. When we collect a fossil from a rock deposit, we assume that the species represented by this fossil lived at the place and time the rock was formed. If we sample a younger deposit and find that the species is not present, and if it never reappears in still younger deposits, we assume the species has become extinct, and that the time of extinction corresponds to the date of the youngest observed fossils.

But there may be other explanations for the absence of the species in younger deposits. For example, the species may have become extinct in this particular region, but survived to later times in other areas. Or the younger deposits may record an environment in which the species never occurred in the first place. A third possibility is that natural selection changed the appearance of the species to such an extent that palaeontologists mistakenly assign younger members to a different species.

A chart of extinctions

These problems mean that we are only just beginning to compile reliable data on how extinctions have varied over time. And such data is essential if we want to test different hypotheses on what has caused extinctions.

Click the image to see a larger version
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http://www.firstscience.com/site/articles/macleod.asp
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Figure 1. Extinctions over the past 600 million years - mass extinctions show up as peaks superimposed on a general decline in extinctions (diagonal line). The mass extinction marked as 'Maastrichtian' was the death of the dinosaurs.
Reference:
Sepkoski, JJ, Jr. 1994. Extinction and the fossil record. Geotimes March 15 - 17

Figure 1 shows one of the latest summaries of extinction data. It concentrates on invertebrates - such as snails, clams and coral species - that lived in ancient oceans. The graph shows the number of extinctions that occurred within successive small subdivisions of geological time - called stages - which are typically a few million years in duration.

There are two particularly noteworthy features. First, there is a general decline in the number of extinctions over the last 600 million years. Secondly, there are several major �peaks� of extinction, which are roughly evenly spaced. Both of these features are spurring a vigorous debate among palaeontologists.

Extinctions on the decline

The overall trend in Figure 1 shows the number of extinctions decreasing with time. At face value, it means that a species existing in the past was more likely to be wiped out than a species existing now. Is this really the case, and - if so - why?

There are currently three explanations.

The first suggests that the effect isn�t real. It occurs because palaeontologists are more familiar with modern marine organisms than with species from the remote past. When dealing with recent fossils, palaeontologists can be fairly confident that they are classifying them correctly into different species and groups of species (genera). When they look back to more ancient and unfamiliar fossils, they are more likely to be fooled into separating them out into many more genera. So there�s a higher chance that one of these - artificially small - ancient genera would become extinct.

The second invokes marine organisms moving from the general ocean into �marginal� environments, for example around the edges of continents. Here, they might be sheltered from environmental changes, and so suffer less extinctions. On the other hand, the marginal environment might play the opposite role. It could be so extreme that the species had to evolve into a hardier form, which was then immune to all but the most profound episodes of global environmental change.

The third (and most recent) explanation argues that conditions in the world's oceans have become progressively more favourable for marine life. In 1994, Prof. Ron Martin of The University of Delaware summerized geochemical evidence that the oceans themselves have changed over geological time, by studying isotopes of elements such as sulphur-34, strontium-87 and carbon-13. These trends match the declining extinction curve.

Ocean changes

In Martin's model, the oceans of 600 million years ago were very different from those of today. Their circulation was sluggish, with large areas of the ocean floor covered by waters with little or no dissolved oxygen. They received large amounts of nutrient washed off from the barren continents (plants and soils had not yet evolved). And ocean plankton was relatively inefficient at producing organic materials through photosynthesis.

As time went by, the oceans became more dynamic as plate tectonics pushed the continents around. Life on land trapped the nutrients that once ran off into the seas. As a result, the oceans became host to a greater diversity of plankton. This, in turn, meant they could support a diverse array of species, increasing the stability of marine ecosystems - and decreasing the probability of extinction.

Mass extinctions: the three culprits

The second important pattern we can see in Figure 1 are �peaks,� where large numbers of species (up to 90%) become extinct within a short period of time. These are termed mass extinctions. The most famous - though not the most severe - involved the �death of the dinosaurs� about 65 million years ago.

Scientists have proposed many different mechanisms to account for the pattern of mass extinctions over the last 600 million years. Currently, the most popular are: a fall in sea level; vast eruptions of basalt; and the impact of an asteroid or comet.

Interestingly, it�s not the direct effects that cause the damage. In all three cases, researchers explain the extinctions through subsequent drastic changes in the environment. For example, they may cool the Earth by promoting the formation of clouds, or lead to global warming as greenhouse gases are released. Nitrogen and sulphur compounds thrown into the atmosphere may produce acid rain, and also destroy the ozone layer.

Patterns of extinction

Generally, it�s difficult link any particular catastrophic event to a subsequent mass extinction. Instead palaeontologists comparing the pattern of mass extinctions as a whole with the patterns of each of the three possible mechanisms. Figure 2 compares the record of mass extinctions with geological records of sea-level falls, flood-basalt eruptions, and impacts of bolides (asteroids or comets).

Figure 2. The record of extinctions (bottom), compared with - from top - major sea-level changes, giant eruptions of basalt, and impact craters.
References:

Looking at Figure 2, it is clear that impacts show the worst record of association with mass extinction events. Sizeable impacts are as likely to have occurred during low-extinction stages as during high-extinction stages. In fact, there�s only one compelling example of an association between a large impact and a major extinction event. The Chicxulub event of 65 million years ago was the largest impact of the last 600 million years, and third largest in the known history of our planet. It blasted out a large crater in Mexico. At the same time, we find the Maastrichtian mass extinction event, also known as the K/T mass extinction. This was the disaster in which the dinosaurs perished, and it is ranked as the third to fifth largest extinction event of the last 600 million years.

Moving on to the second possible mechanism, abrupt falls in sea level show a rather better level of association with extinctions. Each of the three largest mass extinctions during the last 250 million years (the time interval for which we have the most accurate time resolution) corresponds to a major sea-level change. This supports the idea that rapid falls in sea level have a detrimental effect on the diversity of marine invertebrates.

Giant eruptions

But the strongest association - by far - comes with the third prospective extinction mechanism, as seen in the record of continental flood-basalt eruptions. These are vast outpourings of basaltic lava, similar to the eruptions responsible for the Hawaiian Island chain, but taking place entirely on land.

Perhaps the best known is the series of eruptions that took place on the Indian subcontinent beginning at the very end of the Maastrichtian stage, 66.5-64.5 million years ago. They poured out over one million cubic kilometres of lava in just over one million years, forming the vast Deccan Traps. The eruption did not take place continuously over the entire million years, but episodically in massive lava flows that have no counterpart in human history.

Since we have no direct experience of such cataclysmic eruptions, it is difficult to imagine (much less model) the climatic effects. Regardless, the close association between the flood-basalt record and the pattern of extinction events is very difficult to explain away as mere coincidence. In addition, it�s worth noting that the three largest extinctions of the last 250 million years took place during times of combined sea-level fall and flood-basalt eruption. Of course, the Maastrichtian event is also associated with the Chicxulub impact. However, this event is by no means the largest mass extinction to have occurred and, according to available data on the timing and magnitudes of impacts, several extinction events of equal and greater magnitude are not associated with large asteroid impacts.

Weighing up the evidence

As far as any single extinction event is concerned, in all probability we will never know all the factors involved. Nevertheless, the existing data provide an insight into the factors that are repeatedly associated with extinction events in the geological record.

A simple statistical analysis of the data in Figure 2 reveals the relative strength of the association between each type of catastrophe and mass extinctions as follows:

sea-level change 7 out of 14
continental flood basalt eruptions (over the last 250 million years) 10 out of 10
asteroid impact 1 out of 17.
Based on current data, tectonic factors - giving rise to flood-basalt volcanism and sea-level fall - appear to exhibit the greatest level of association with large-scale extinction events over the course of the last 600 million years.
Extraterrestrial impacts - current darlings of the media coverage of extinctions - have certainly played an important role in Earth history and may have enhanced the �death of the dinosaurs.� However, asteroid impacts do not appear to be the primary agents responsible for the overall patterns in the geological extinction record.

Dr Norman MacLeod is an international expert in the study of extinctions. After a BSc in geology from the University of Missouri, he received an MSc from the Southern Methodist University and a PhD from the University of Texas, both in palaeontology. Norm MacLeod has researched at the University of Michigan and Princeton University, and is now a member of the Palaeontology Department at The Natural History Museum, London. As well as extinctions, his research interests include the quantitative analysis of morphology and the analysis of evolutionary patterns.

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Tyler R.T.

Edited by Tyler 06-18-01

[This message has been edited by William E. Tibbe (edited 06-18-2001).]

Boltman is on the right track. When this nonsense about hunting on the part of early Americans being responsible for the extinction of megafauna in North America first came out some years ago I wrote the guy responsible for pushing that notion and acquainted him with his own biases and intellectual near-sightedness. How is it possible that humans wiped out the mastodon, mammoth, smilodon, giant sloth, giant bison, giant elk and other species, leaving uncounted numbers of modern bison thriving on the plains? Even the introduction of horses to the native Americans did not result in any significant reduction in bison populations. Or deer or any other large species.

The fact is that the geologic record contains numerous indicators of a global climatic disruption of uncertain nature at the very time that the megafauna disappeared both. Very large animals are especially vulnerable to severe shocks to the environment because they depend on the so much larger a portion of the natural resources. Mammoth have been found frozen with green grass in their mouths. That sounds like a sudden climate change to me, not a slip on the ice.

What you have to remember is the essential requirement in academia to establish a reputation. "Publish or perish" is the law. The only ways to attain prominence is by putting forward "revolutionary" ideas and by getting it right. In areas where crackpot theories are virtually immune to being disproved (as in anthropology and astronomy) they abound.

Dr. MacLeod is correct in highlighting the significance of the Deccan Traps upheaval at the K-T boundary, but his arguments against asteroid impact as a mechanism for extinction only betray ignorance and prejudice. Incontrovertible evidence of giant asteroid impact has been established for every major extinction of the past, including the K-T event. That impact site is at Chixulub in the Yucatan region of Mexico. Significantly, the Deccan Traps are (or were) at the precise opposite point on the Earth's surface and the vulcanism was triggered by gigantic shock reflections on the crust as the impinging shock waves of the impact wrapped around the planet.

Each of these impact events is identified by a fine layer of sediments containing an incredible increase in the number of fungal spores. What happened was a global firestorm as vast areas of vegetation burned off, followed by a period of darkness lasting many weeks or months. Imagine what your prospects would be if you were a large herbivore dependent on huge quantities of foliage browse each day. On the other hand a small animal might easily survive, and they did. Depending on the severity and extent of the devastation some larger species also survived.

Only COMMERCIAL hunting and the destruction of habitat by farmers and ranchers threatened or actually resulted in extinctions on this continent during the last two centuries. It wasn't subsistence or even sport hunters. Ducks, pidgeons, deer and other game were highly sought by European and Eastern restaurants and the efforts to make a fast buck with no reckon of the effect nearly eliminated big game from North AMerica by the close of the 19th century when conservation efforts - led by sport hunters - took charge and turned it around. The most egregious case was slightly different. The US Government promoted the slaughter of the buffalo for the express purpose of waging genocide on the native Americans and that can be documented. Very little commercial use was put to any of the kills, mainly the hides, sometimes the bones. Our overfishing today is part of the same problem. We have wiped out several old standbys. Ever notice how the fashion in fish changed in the last few years in restaurants? Thats because the yields are plummeting. Reason: no restraint whatsoever and a public demand for freshness at any cost resulting in enormous waste. Huge volumes of fish simply are dumped uneaten.

[This message has been edited by Harald (edited 06-19-2001).]

Thanks for the interesting responses.

The Scientists did make some qualifying statements and admit to some doubts and unsettled differences of opinion. Those fields of science that apply may be considered still juvenile. For example it was not until the 1980's that continental drift was understood and explained. Practically monthly there are announcements of new finds of fossils heretofore unknown.
Perhaps there are many who do not understand that it has only been within the last 200 years or so that mankind has come out of a dark cave, so to speak, into the sunshine, intellectually.

However, there may be two attitudes that a person, or persons, can harbor. How do YOU view the world, earth, future?

The earth's history clearly shows that it is a very dangerous, inhospitable place to live. Human existence is a mere blip compared to the geological calendar, where it is spoken that some species have survived for millions of years. Thus we can have a micro and a macro calendar and attitude.

For example, many species today have been driven to the brink of extinction. Tigers, rhinos, gorillas and many, many other smaller and lesser species. So does it matter on the macro calendar if they disappear. In the long run - no!. Taking into account the 17 periods of extinction above described, the earth will repopulate eventually. We probably won't be alive to see it but it will happen. And there will be new and different species. Consider the devastation when the next ice age occurs and much of North America is buried under a thousand feet, or more, of ice.

Does it matter on the micro calendar - yes! Most of us want to preserve as many species - right now - as possible, during our lifetime. This is probably what drives the arch conservationists and "Anti's" who are opposed to almost everything that pertains to habitat destruction and animal killing.

Can we save the species? Can we save our species? There is growing evidence that we cannot and will not preserve our lifestyle indefinitely. So how much longer until the catastrophe hits. And how long will it take to deplete or devastate so many species?

Reverting back to the original question - Do hunters cause extinction? The answer seems to be yes and no. In some places in some countries they do.In some places in other countries they do not. Thus a simplistic single answer is not appropriate. There are many aspects and extenuating circumstances to take into account. But it is the long run that counts?

Tyler T.R.