The Extinction of Australian Megafauna
Until 30-40,000 years ago, Australia was home to wombats the size of rhinos, seven-meter-long lizards and three-metre tall kangaroos. These megafauna were probably eliminated due to human-induced climate change like that which is happening to the Amazon. Today, wide-scale burning of the Amazon runs the risk of turning rainforest into savannah. In a rainforest, 50 per cent of rainfall gets recycled by the ecosystem. Rain falls, is trapped, sucked up by trees, released into the atmosphere, reaches a critical humidity and then falls again at a different location. When the land is cleared; however, not only does less recycling occur, less rain falls. The ecosystem then collapses forever.
50,000 years ago in Australia, large-scale burning of the land likewise turned rainforest into savannah, and then into desert. After the foliage was razed to the ground, rain fell and soaked into the sand or quickly evaporated under the scorching sun. In turn, a reduction in humidity decreased the number of clouds forming.
In 2004 and 2005, Dr John Magee and Dr Michael Gagana from the Australian National University showed that burning caused a decrease in the exchange of water vapour between the biosphere and atmosphere. Clouds stopped forming and the annual monsoon over central Australia failed. Whereas once the Nullarbor Plain was home to forests and tree dwelling Kangaroos, now it is desert. Likewise, Lake Eyre, formerly a deep-water lake in Australia's interior, is now a huge salt flat occasionally covered by ephemeral floods. (1) A small change caused a chain reaction that led to a large change.
The revelations of human-induced climate change married the previous two competing theories regarding the extinction of the megafauna. Previously, one group of scientists had argued that natural climate change caused the extinctions. This approach failed to explain why the megafauna had survived more extreme climatic changes over the last 1.5 million years. Another group of scientists had argued that humans had hunted megafauna to extinction. This approach failed to explain why the fossil record showed evidence of ecosystem collapse associated with climatic change.
After human-induced climate change caused the rains to fail, it became impossible for humans to remain in balance with the ecosystem. When Australia had been fertile, human population densities had been high and may have been in balance with megafauna. When the ecosystem collapsed, they used their skills of adaptation to hunt megafauna to extinction.
Megafauna and humans co-existing
Cuddle Springs in north central NSW is currently the only place in Australia where evidence has been found of megafauna and humans co-existing. Excavations by a team from the University of Sydney has found evidence that megafauna were living at the site 30,000 years ago. If correct, this means that they must have survived the human-induced climate change and also lived alongside humans for a further 15,000 years.
Because the megafauna bones don't contain detectable amounts of protein, no direct dating methods have been used. Instead, they have been dated according to the layers of dirt around them. Consequently, some scientists have disputed the ages because the process of site formation may have involved some mixing of materials of different ages. This mixing may have created a perception of co-existence where none actually occured.
If one takes a view that the University of Sydney's estimates are accurate, there is a small chance that the megafauna was farmed by humans. If humans were farming the Megafauna, they could have preserved them at Cuddle Springs long after they had been hunted to extinction around the rest of Australia.
The now extinct Diprotodon may have been suitable for animal husbandry. Weighing 32 times as much as a Red Kangaroo, it could have been enclosed in a pen and humans could have fed on its blood, milk and flesh. The Genyornis was another. A flightless bird four times larger than an Emu, it could have been enclosed in a pens and humans could have fed on its eggs and flesh.
There is some evidence of farming. An unusual feature of the dig at Cuddle Springs is that the Diprotodon is one of the few animals that was associated with human butchering tools. If the humans were merely hunter gatherers, many of the smaller animals should also also have lived alongside them and should have also been associated with butchering tools. The fact that the butchering tools have only been associated with the larger animals suggests that the humans lived off the larger animals.
Grinding stones, which are typically found in agricultural societies, are the only direct evidence of farming at Cuddle Springs. The presence of 30,000-year-old grinding stones at Cuddle Springs is quite unusual because they predate all other grinding stones around the world by 20,000 years. Hunter gatherers just don't use grinding stones.
*At present, no researchers argue that the humans that existed at Cuddle Springs were anything other than hunter gatherers.
Dissenting views
The theory of human-induced climate change proposed by Dr John Magee and Dr Michael Gagana is not universally accepted. Other scientists propose some alternative theories.
Natural climate change was the cause of Megafauna extinction
In 1998 David Bowman, an ecology expert from Charles Darwin University, argued that humans did not have the population density or the technology to efficiently wipe out megafauna. According to Bowman:
"It should be remembered that it becomes increasingly difficult to kill off a species as their population is reduced to low levels because of the extra hunting effort required to find the last remaining animals." (2)
While Bowman was correct in his assertion that a decline in prey numbers would necessitate more work on behalf of the hunters, common sense would also stipulate that as numbers decline, a species' genetic diversity declines with it. Whether the last animal dies as a result of a spear or disease is irrelevant because it was over hunting the caused population decline. Certainly humans managed to hunt the Tasmanian Tiger into extinction even though population decline required more effort to hunt them.
As an alternative to the over-hunting theory, Bowman proposed that the megafauna were wiped out by climactic changes. In Bowman's opinion, these climate changes had nothing to do with human action. To the contrary, human action limited the severity of climate change. According to Bowman:
"They intervened and they changed the habitat balance with their fire management practices and, in doing so conserved some habitats, such as rainforest, that might otherwise have been lost during the extreme aridity that characterised the end of the last ice-age some 10,000 to 20,000 years ago." (2)
Like his theory that a decline in population would somehow save a species, Bowman's theory that burning forests somehow preserved them was also on the silly side. By Bowman's logic, people today should counter the threat of global-warming-induced drought by investing in some flame throwers. Fire does not help ecosystems. It does not magically infuse water or nutrients. The explosion of greenery sometimes seen after a fire is simply a case of plant species using weakness in the ecosystem as the best time to push for individual dominance.
A final problem with Bowman's theory is that almost all the biggest animals appear to have gone extinct well before the ice age reached its maximum, and at least 20,000 years before the megafauna from nth America went extinct. If the climate change was a global phenomenon, megafauna extinction around the world should have happened at a similar time. The Australian extinctions were before other countries.
University of Queensland PhD researcher Gilbert Price is another who supports the climate change theory of megafauna extinction. Price studied a 10-metre-deep section of creek bed in the Darling Downs region in Queensland's southeast. He found evidence of a very severe drought around 40-50,000 years ago, and megafauna dying, but no evidence of humans. According to Price,
"The research found no evidence of humans being involved in the accumulation of fossils in the catchment at the time of deposition, but is perfectly consistent with their decline being caused by increasing aridity...So it's most likely that Australia's giant kangaroos and other megafauna in this area were driven to extinction by the hands of Mother Nature." (4)
Price's research was useful in that it showed that there was very severe climate change 40-50,000 years ago in the Darling Down's region. It was not very useful in explaining megafauna extinction. Fossils only form when a dead animal is buried and the body is cut off from oxygen and water. Generally, when humans kill an animal, they do not bury the remains so few fossils form. Consequently, it would not be expected to find evidence of humans killing megafauna unless the region has some kind of mud slides that buried bodies.
Even if humans were not killing megafauna in Darling Downs, just because an animal is dying in a drought in one part of a country doesn't mean humans aren't hunting them in another. I.e, just because Kangaroos die in a drought in Victoria doesn't mean people aren't shooting them in Western Australia, or hunting them in areas where they could have potentially survived a drought. Price was trying to make his research appear more significant than it was. All that his research indicated was that there was climatic change in the Darling Downs region 40-50,000 years ago. His research didn’t show the cause of that climate change or what humans did during the climate change.
Hunting was the cause of megafauna extinction
Flinders University palaeontologist Gavin Prideaux has argued that the megafauna were hunted by humans. According to Prideaux:
"Our evidence show that the Naracoorte giants perished under climatic conditions similar to those under which they previously thrived, which strongly implicates humans in their extinction...the real issue now is trying to resolve whether it was hunting or whether it was landscape destruction through burning ... and a bit of both is more likely." (3)
Prideaux's view doesn't seem to incorporate research from the ANU showing human-induced climate change. Furthermore, it doesn't seem to incorporate some research showing a relationship between climate change and megafauna extinction. According to the ANU's Dr John Magee and Dr Michael Gagan:
"Neither over-hunting nor human-induced diseases, the two most widely cited alternative agents for a human-caused extinction event in Australia, would result in the dramatic changes at the base of the food web documented by our datasets,...the reduction of plant diversity, however it came about, would have led to the extinction of specialized herbivores and indirectly to the extinction of their non-human predators." (1)
Until 30-40,000 years ago, Australia was home to wombats the size of rhinos, seven-meter-long lizards and three-metre tall kangaroos. These megafauna were probably eliminated due to human-induced climate change like that which is happening to the Amazon. Today, wide-scale burning of the Amazon runs the risk of turning rainforest into savannah. In a rainforest, 50 per cent of rainfall gets recycled by the ecosystem. Rain falls, is trapped, sucked up by trees, released into the atmosphere, reaches a critical humidity and then falls again at a different location. When the land is cleared; however, not only does less recycling occur, less rain falls. The ecosystem then collapses forever.
50,000 years ago in Australia, large-scale burning of the land likewise turned rainforest into savannah, and then into desert. After the foliage was razed to the ground, rain fell and soaked into the sand or quickly evaporated under the scorching sun. In turn, a reduction in humidity decreased the number of clouds forming.
In 2004 and 2005, Dr John Magee and Dr Michael Gagana from the Australian National University showed that burning caused a decrease in the exchange of water vapour between the biosphere and atmosphere. Clouds stopped forming and the annual monsoon over central Australia failed. Whereas once the Nullarbor Plain was home to forests and tree dwelling Kangaroos, now it is desert. Likewise, Lake Eyre, formerly a deep-water lake in Australia's interior, is now a huge salt flat occasionally covered by ephemeral floods. (1) A small change caused a chain reaction that led to a large change.
The revelations of human-induced climate change married the previous two competing theories regarding the extinction of the megafauna. Previously, one group of scientists had argued that natural climate change caused the extinctions. This approach failed to explain why the megafauna had survived more extreme climatic changes over the last 1.5 million years. Another group of scientists had argued that humans had hunted megafauna to extinction. This approach failed to explain why the fossil record showed evidence of ecosystem collapse associated with climatic change.
After human-induced climate change caused the rains to fail, it became impossible for humans to remain in balance with the ecosystem. When Australia had been fertile, human population densities had been high and may have been in balance with megafauna. When the ecosystem collapsed, they used their skills of adaptation to hunt megafauna to extinction.
Megafauna and humans co-existing
Cuddle Springs in north central NSW is currently the only place in Australia where evidence has been found of megafauna and humans co-existing. Excavations by a team from the University of Sydney has found evidence that megafauna were living at the site 30,000 years ago. If correct, this means that they must have survived the human-induced climate change and also lived alongside humans for a further 15,000 years.
Because the megafauna bones don't contain detectable amounts of protein, no direct dating methods have been used. Instead, they have been dated according to the layers of dirt around them. Consequently, some scientists have disputed the ages because the process of site formation may have involved some mixing of materials of different ages. This mixing may have created a perception of co-existence where none actually occured.
If one takes a view that the University of Sydney's estimates are accurate, there is a small chance that the megafauna was farmed by humans. If humans were farming the Megafauna, they could have preserved them at Cuddle Springs long after they had been hunted to extinction around the rest of Australia.
The now extinct Diprotodon may have been suitable for animal husbandry. Weighing 32 times as much as a Red Kangaroo, it could have been enclosed in a pen and humans could have fed on its blood, milk and flesh. The Genyornis was another. A flightless bird four times larger than an Emu, it could have been enclosed in a pens and humans could have fed on its eggs and flesh.
There is some evidence of farming. An unusual feature of the dig at Cuddle Springs is that the Diprotodon is one of the few animals that was associated with human butchering tools. If the humans were merely hunter gatherers, many of the smaller animals should also also have lived alongside them and should have also been associated with butchering tools. The fact that the butchering tools have only been associated with the larger animals suggests that the humans lived off the larger animals.
Grinding stones, which are typically found in agricultural societies, are the only direct evidence of farming at Cuddle Springs. The presence of 30,000-year-old grinding stones at Cuddle Springs is quite unusual because they predate all other grinding stones around the world by 20,000 years. Hunter gatherers just don't use grinding stones.
*At present, no researchers argue that the humans that existed at Cuddle Springs were anything other than hunter gatherers.
Dissenting views
The theory of human-induced climate change proposed by Dr John Magee and Dr Michael Gagana is not universally accepted. Other scientists propose some alternative theories.
Natural climate change was the cause of Megafauna extinction
In 1998 David Bowman, an ecology expert from Charles Darwin University, argued that humans did not have the population density or the technology to efficiently wipe out megafauna. According to Bowman:
"It should be remembered that it becomes increasingly difficult to kill off a species as their population is reduced to low levels because of the extra hunting effort required to find the last remaining animals." (2)
While Bowman was correct in his assertion that a decline in prey numbers would necessitate more work on behalf of the hunters, common sense would also stipulate that as numbers decline, a species' genetic diversity declines with it. Whether the last animal dies as a result of a spear or disease is irrelevant because it was over hunting the caused population decline. Certainly humans managed to hunt the Tasmanian Tiger into extinction even though population decline required more effort to hunt them.
As an alternative to the over-hunting theory, Bowman proposed that the megafauna were wiped out by climactic changes. In Bowman's opinion, these climate changes had nothing to do with human action. To the contrary, human action limited the severity of climate change. According to Bowman:
"They intervened and they changed the habitat balance with their fire management practices and, in doing so conserved some habitats, such as rainforest, that might otherwise have been lost during the extreme aridity that characterised the end of the last ice-age some 10,000 to 20,000 years ago." (2)
Like his theory that a decline in population would somehow save a species, Bowman's theory that burning forests somehow preserved them was also on the silly side. By Bowman's logic, people today should counter the threat of global-warming-induced drought by investing in some flame throwers. Fire does not help ecosystems. It does not magically infuse water or nutrients. The explosion of greenery sometimes seen after a fire is simply a case of plant species using weakness in the ecosystem as the best time to push for individual dominance.
A final problem with Bowman's theory is that almost all the biggest animals appear to have gone extinct well before the ice age reached its maximum, and at least 20,000 years before the megafauna from nth America went extinct. If the climate change was a global phenomenon, megafauna extinction around the world should have happened at a similar time. The Australian extinctions were before other countries.
University of Queensland PhD researcher Gilbert Price is another who supports the climate change theory of megafauna extinction. Price studied a 10-metre-deep section of creek bed in the Darling Downs region in Queensland's southeast. He found evidence of a very severe drought around 40-50,000 years ago, and megafauna dying, but no evidence of humans. According to Price,
"The research found no evidence of humans being involved in the accumulation of fossils in the catchment at the time of deposition, but is perfectly consistent with their decline being caused by increasing aridity...So it's most likely that Australia's giant kangaroos and other megafauna in this area were driven to extinction by the hands of Mother Nature." (4)
Price's research was useful in that it showed that there was very severe climate change 40-50,000 years ago in the Darling Down's region. It was not very useful in explaining megafauna extinction. Fossils only form when a dead animal is buried and the body is cut off from oxygen and water. Generally, when humans kill an animal, they do not bury the remains so few fossils form. Consequently, it would not be expected to find evidence of humans killing megafauna unless the region has some kind of mud slides that buried bodies.
Even if humans were not killing megafauna in Darling Downs, just because an animal is dying in a drought in one part of a country doesn't mean humans aren't hunting them in another. I.e, just because Kangaroos die in a drought in Victoria doesn't mean people aren't shooting them in Western Australia, or hunting them in areas where they could have potentially survived a drought. Price was trying to make his research appear more significant than it was. All that his research indicated was that there was climatic change in the Darling Downs region 40-50,000 years ago. His research didn’t show the cause of that climate change or what humans did during the climate change.
Hunting was the cause of megafauna extinction
Flinders University palaeontologist Gavin Prideaux has argued that the megafauna were hunted by humans. According to Prideaux:
"Our evidence show that the Naracoorte giants perished under climatic conditions similar to those under which they previously thrived, which strongly implicates humans in their extinction...the real issue now is trying to resolve whether it was hunting or whether it was landscape destruction through burning ... and a bit of both is more likely." (3)
Prideaux's view doesn't seem to incorporate research from the ANU showing human-induced climate change. Furthermore, it doesn't seem to incorporate some research showing a relationship between climate change and megafauna extinction. According to the ANU's Dr John Magee and Dr Michael Gagan:
"Neither over-hunting nor human-induced diseases, the two most widely cited alternative agents for a human-caused extinction event in Australia, would result in the dramatic changes at the base of the food web documented by our datasets,...the reduction of plant diversity, however it came about, would have led to the extinction of specialized herbivores and indirectly to the extinction of their non-human predators." (1)