Hunting or climate change? Megafauna extinction debate narrows

By Christopher Johnson, University of Tasmania

What is the oldest debate in Australian science? Probably, the argument over what caused extinction of our Pleistocene megafauna – the diprotodons, giant kangaroos, marsupial tapirs, über-echidnas and other big and bizarre creatures that used to live here.

Giant Haast's Eagle attacking New Zealand Moa
[John Megahan, PLoS Biology, CC BY- 2.5]

In 1877 the great English anatomist Sir Richard Owen suggested that these big animals had been driven extinct by “the hostile agency of man”. That is, hunting did it, in a process we now call overkill. Other people responded that climate change must have been the cause, and it was on.

A string of recent studies from a wide range of disciplines – geochronology, palaeoecology, palaeontology, and ecological modelling – have supported Owen’s opinion. But the argument continues. Why?

The main reason is that many Australian archaeologists reject overkill. They have looked for direct evidence that people killed megafauna, and they haven’t found it. No great piles of bones around ancient campsites; no diprotodon skeletons with spears stuck in their ribs; no arsenal of specialised weapons for bringing down large prey. Very few archaeological sites even have remains of people and megafauna in close association.

Some archaeologists conclude that megafauna-hunting just did not happen, or if it happened it was rare and insignificant. Often this conclusion is stated with a ringing confidence that dismisses all non-archaeological evidence for overkill.

But they have not asked a crucial question: if people did hunt megafauna to extinction, how much evidence of killing should we now be able to get from archaeological sites? A new paper by archaeologists Todd Surovell and Brigid Grund suggests the answer to that question is “very little or none”.

Surovell and Grund point out, first, that the period when archaeological evidence of killing of megafauna could have been formed is a small fraction of the total archaeological record of Australia. People arrived here between about 50,000 and 40,000 years ago. This is also the interval during which animals like diprotodon disappeared. A comparison of archaeological and fossil dates suggests humans and megafauna overlapped for only about 4,000 years continent-wide, and modelling suggests that if hunting caused extinction it would have been all over in less than 1,000 years in any place.

This means that no more than 8%, perhaps as little as 2%, of the Australian archaeological record covers the period of human-megafauna interaction. The “smoking gun” evidence of overkill should therefore be rare. Surovell and Grund show that the problem of finding such evidence is even worse than that, for two reasons.

First, when people first arrived their populations were necessarily small. Living sites therefore occurred at low density. As population size grew exponentially, site density increased. So, the very earliest sites must be far rarer than later ones.

But if overkill happened, populations of megafauna would have been going down as humans went up: as the density of sites was rising the proportion of them that could have contained evidence of megafauna kills was falling. Thus, sites with potential to preserve that evidence are actually a tiny proportion, perhaps much less than .01%, of the total archaeological record.

Second, material in archaeological sites degrades with time due to breakdown, weathering and scavenging of bone and removal by erosion. Old sites are eventually buried under sediments. The probability of discovering archaeological sites from the earliest occupation of Australia is intrinsically much lower than for later times, and most of the contents of those sites will have disappeared.

In fact, the very oldest archaeological sites in Australia typically contain only a few stone tools. They can tell us very little about interaction of the first Australians with any animals or plants, let alone reveal a picture of megafauna-killing.

Our fundamental task as scientists is to test hypotheses using evidence. To test the overkill hypothesis, we need a kind of evidence that would differ according to whether the hypothesis is true or false. Obviously, if overkill did not happen, evidence of megafauna-killing should be rare in the archaeological record. But, Surovell and Grund’s analysis makes it clear that if overkill happened, we should still expect evidence of killing to be rare. Therefore, failure to find such evidence does not amount to a test of the overkill hypothesis.

This does not mean that archaeological evidence of killing (or absence of such evidence) is useless in testing the overkill hypothesis. Surovell and Grund show it can be useful, by comparing the archaeological records of Australia, North America and New Zealand. All three places lost their megafaunas when people arrived, but this happened a very long time ago in Australia, and very recently (700 years ago) in New Zealand. North America is intermediate, with human arrival and extinction from 14,000 to 13,000 years ago.

Applying the same logic to all three cases, we predict that if overkill caused megafaunal extinction in each place the archaeological evidence of killing should be abundant in New Zealand, rare in North America, and vanishingly rare in Australia. That is exactly what we find.

There is so much evidence showing New Zealand’s moa were heavily hunted that nobody doubts overkill was the main cause of their extinction. In North America, there are undoubted kill sites for mammoths, mastodons and a few other species, but this evidence is far thinner than in New Zealand. Australian archaeology is yet to reveal any convincing evidence for megafauna-killing.

So, far from disproving overkill, the archaeological evidence from Australia is actually consistent with the overkill hypothesis.

About the Author

Christopher Johnson is an ecologist, interested in pure and applied ecology, environmental history, the biology of extinction, conservation and wildlife management. He is a Professor of Wildlife Conservation and ARC Australian Professorial Fellow at University of Tasmania.

Christopher Johnson receives funding from the Australian Research Council.

This article was originally published at The Conversation. Read the original article.

By Alan Harvey, University of Western Australia

Christine Westerback/Creative Commons

All human cultures and social groups that we know of respond to music and dance. The type of music may vary but the underlying, fundamental principles of making music are the same.

Our recognition of, and emotional responses to, pleasant and unpleasant music seems to be universal, expressed even in very young infants and seemingly independent of our cultural upbringing.

So what exactly is music for? Why is it a universal that can profoundly affect people, why is it such an essential part of our lives?

Music is a form of communication which is different from language. In humans, music stimulates emotions and elicits autonomic and physiological responses. It entrains neural activity and is inextricably linked to movement and dance.

Music facilitates interactions within groups and can create common arousal states. It helps to provide cohesion and organisation to our social architecture.

Throughout recorded history, leaders – whether of nations, political parties or religious denominations – have understood the power of music to influence populations.

In recent times, researchers have shown that music structures time and provides mnemonic frameworks that aid learning and memory, help organise knowledge. Many of us can remember the lyrics of songs for example, but may not remember much, if any prose.

Attaching words to music somehow makes the words easier to memorise. Yet despite all of this, the impact of music remains mysterious: it does not seem to do anything, it does not transmit data and information in the same way as language/speech.

For many, the evolution of language in Homo sapiens is a unique event that is linked to the evolution of the cognitively modern mind. What then is the relationship between music and language, and to what extent are they dependent or independent of each other?

Human Brain [MRI Scan]
taod/Creative Commons

Our brains are known to be wired to process both forms of communication, but from an evolutionary point of view did music come before language, or vice versa, or was there a common precursor that somehow separated into two systems when Homo sapiens evolved, with both types of communication retained?

Was music an important element that contributed to the early well-being of our species? What, if any, advantages did music give to Homo sapiens from an evolutionary perspective as our founders migrated out of east Africa to colonise the planet?

Why does music continue to exist alongside language and remain important to all human cultures, thousands of generations after the founders of our species evolved?

Modern neuroscience research, especially using new imaging techniques such as positron emission tomography (PET) and functional Magnetic Resonance Imaging (fMRI) confirms that the processing of music has a consistent structural foundation in the human brain.

It has been known for some time that, in right-handed individuals, language is mostly processed in the left cerebral hemisphere while many aspects of music involve right hemisphere activity.

But new imaging data have revealed even more complex circuitries involved in music and language processing. Numerous regions of the brain are integrated into networks that subserve music or language processing and analysis, but the neuroimaging data also show that separation of these processing streams is by no means complete.

For example, there is overlap in brain areas that process the emotional (prosodic) aspects of music and speech, and studies have shown that musical training results in a shift towards processing in the left cerebral hemisphere.

As research continues, more is learned about how music-related circuits differ from, or overlap with, other pathways involved in cognitive and emotional processing. For example, brain areas associated with positive responses to music overlap with networks associated with reward behaviours, subjective experiences and acts of social cooperation.

In close association with the evolution of the modern mind, I believe music was of critical importance to our early ancestors; increased fitness and reproductive advantage of a group is gained not only by an individual’s success but also if cooperative behaviours benefit other members of the group, and importantly for our ancestors these benefits extended to others who were not necessarily genetically related.

For most people, music therapy remains a branch of “alternative” medicine, something outside the mainstream. But recent research suggests that it is time that this attitude was changed.

For example, training in music has measurable effects on brain plasticity and can influence learning ability during development. Music also seems to have mnemonic powers, activating circuits in the brain that are linked to aspects of memory processing.

There are also structural changes in developing brains associated with early musical training, and exposure to music seems to have beneficial effects on children suffering from developmental disorders such as autism and Williams syndrome.

In adults, many studies have shown that music used with physical therapy improves motor control and coordination, with benefits for rehabilitation after injury or in degenerative conditions such as Parkinson’s disease.

Music therapy may also improve memory recall and social awareness in Alzheimer’s patients and recent studies on stroke patients have shown that controlled exposure to music improves cognitive function, increases motivation and awareness, and enhances positive mood states.

Taken together, the evidence suggests that music remains just as essential to Homo sapiens now as it was 70,000-80,000 years ago. It continues to be important for development of our children, for our health and for our overall sense of mental well-being.

Above all, music is perhaps the primary medium which enables individual members of the species Homo sapiens to forget their mortal vulnerability and come together as a collective group to share and enjoy common physiological and emotional experiences.

About the Author

Alan Harvey was educated at the University of Cambridge and Australian National University. He is currently Professor and Deputy Head of the School of Anatomy and Human Biology. He has the long-term ambition of bringing his neuroscience and musical interests together, intending to write a book about the role of music in human evolution and modern-day society.

Alan Harvey receives funding from the NHMRC, ARC and WA Neurotrauma Research Program.

This article was originally published at The Conversation. Read the original article.

There are many different beliefs about evolution prior to Charles Darwin. These began during the 17th century up into the early 19th century. In the 17th century, James Ussher, a Anglican archbishop of Armagh in northern Ireland, reinforced a traditional Judeo-Christian version of creationism. He fixed the date of creation at 9:00 am, October 23, 4004 B.C.

In the 18th century the Swedish botanist Carl Linneaus, classified organisms based on categories; genus and species. The concept of genus and species was actually developed by John Ray in the 1600’s, but it was Linneaus who used the system to name modern humans homo sapiens and placed modern humans in the order primates, with apes, monkeys, and prosimians. This was controversial at the time because it implied that people were part of nature, alongside animals and plants.

Before, it was believed that life forms were fixed, denying any evolutionary change. French mathematician and naturalist, George Louis Leclerc, Comte de Buffon, said that living things do indeed “evolve” over long periods of time, unnoticeable to humans, due to influences from environments or even chance. He also believed that the earth is much older than 6000 years old (at least 75,000... We now know it is much much older!!).

In the late 18th century, evolutionists Eramus Darwin, grandfather of the Charles Darwin, believed that evolution has occurred in living things, including humans, but was rather confused of why and what was responsible for this change. In his later work he suggested that earth and life on it have been evolving for “millions of ages before the commencement of the history of mankind.”

Other than evolution in organisms, change in the earth as a whole has been carefully examined. Catastrophic events helped shaped the world we live in today. Charles Lyell documented that earth is very old and that natural processes such as volcanoes, earthquakes, glacier movements, in the past operate as they do today. Lyell provided evidence for the theory of uniformitarianism, developed by Scottish geologist, James Hutton, the idea that forces acting today, were the same as in the past.

Read more about Pre-Darwinian Theories!

About the Author

I'm Jose Pierre and I like learning about all aspects of culture, both ancient and modern. I enjoy learning how they communicated, expressed themselves, and their technology.

The following is a media review and summary.

Our planet is the only known planet that can sustain life. But life on earth has developed into a vast collection of species over time. In all, there are over 100 million species on earth. There are over 200 species of monkeys, 1000 different species of bats, over 350,000 species of Beatles, and over 250,000 species of flowering plants. David Attenborough wrote and presented "Charles Darwin and the Tree of Life" to show the remarkable past of Charles Darwin and his contemporaries, and the theory of natural selection, evolution, and diversity.

Charles Darwin Seated

Henry Maull (1829–1914) and John Fox (1832–1907)  

Charles Darwin was the companion of the captain of ship, The Beagle, at the age of 22. They landed in Brazil and the Galapagos Island. Their he found several species of beetles. He examined every single one he found and took specimens since he liked insects. Later finding a diversity of tortoises and finches, he wondered why they look so different. He then continued looking about the island documenting his finds. 

Finally he developed the theory that species of animals are not fixed, species slowly change throughout time. 

How could animals of the same species develop different characteristics? He named this natural selection. Natural selection means that the fittest within a species survive within the environment. 

Certain traits and characteristics can help the individual survive its environment and allow it to reproduce. The traits are then passed to the offspring over time, that specific trait needed to survive in the specific environment becomes more frequent in offspring.

Darwin's
On the Origin of Species

An example of natural selection Darwin used was the different beaks within the finches and the different shells the tortoises had. The finches with a thin beak are specialized at catching bugs in the air, while the finches with wider sharper beaks are specialized in cracking open nuts to obtain food. Tortoises with a round shell tended to eat food on the ground and tortoises with a peeked shell allowed them to reach higher plants. The different beaks and shells is evidence that certain traits are specialized within a certain environment.

The actions of Charles Darwin proved that species are not fixed. Species slowly change over time to develop traits that best help to survive in their environments.

About the Author

I'm Jose Pierre and I like learning about all aspects of culture, both ancient and modern. I enjoy learning how they communicated, expressed themselves, and their technology.

Nature comes in many sizes: leaf sizes
[bonsaitonight.com]

The size of an animal is not fixed. Size is determined by the environment the animal lives in to maximize its survival. Size determines how much you need to feed, what you’re going to feed, and what’s going to feed on you. Everything depends on size.

The elephant is the largest land animal today with the height up to eight feet to the shoulders. But the elephants’ ancestors, the mammoth, were much larger with the exception of the Pygmy Mammoth. Pygmy Mammoths lived off the coast of California twenty-thousand years ago. An adult Pygmy mammoth stands at five feet, seven inches at the shoulders and were one tenth of the size of their cousin mammoths on the mainland. Why was the Pygmy Mammoth so small? Adaptation. The coast of the island, where the mammoths lived, shrunk due to higher water levels and forced the mammoths to reach higher grounds. The only good food source available was at the top of mountains. Larger mammoths had trouble going up the mountains so they slowly died off. Smaller, more maneuverable mammoths survived and breed so the trait of being smaller was passed on through generations.

Size comparison: elephants and mammoths
[BBC Nature Wildlife]

Insects are known to be small, some only centimeters long. Fossil records show that two-hundred sixty million years ago there were Dragonfly’s with wingspans up to three feet wide, millipedes up to eight feet long, and fly’s the size of small birds. How did insects get so big at that time? Back then oxygen levels in the atmosphere were larger than they are now. The amount of oxygen present determines the size of the insects because with more oxygen intake, the muscles expand to larger sizes and increasing the maximum size or insects. An experiment conducted in the video had normal insects raised in a environment with increased oxygen levels. Today’s levels reach percentages up to twenty-one percent, but the insects used in the experiment were exposed to thirty percent oxygen levels. With this insects grew twenty-five to thirty present larger than normal. If this continued, who knows how big insects can get. But there are some limitations to size such as environmental factors, predators, nutrition, and mobility.

All life forms either grow larger or smaller depending on their environment and ability of survival. But one life form has never gown or shrunk, bacteria. Bacteria is the most essential life form. If humans were to disappear from the face of the earth, ninety percent of species wouldn’t notice. If bacteria were to disappear all life forms will disappear in a matter of hours. 

The Blue Whale is the largest life form that ever lived. Whale ancestors were once land animals but after millions of years and frequent aquatic life, they became completely aquatic. The sudden growth sprout whales went through baffled scientist. How can a large animal like the Blue Whale survive by only eating small creatures such as krill? Blue whales feed on large amounts of krill four hours a day to keep up with energy necessity. Also the buoyancy of water helps counteract the effects of gravity on size limitation. So the whale can grow large without any problems.

Sauropods were the largest land animals to ever live. Sauropods included the Brachiosaurus, the Diplodocus, and the Brontosaurs during the Triassic period about one hundred seventy million years ago. How could these beasts grow up to seventy five feet long and weigh up to thirty tons without any limitations or problems? Back during the Triassic period, carbon dioxide levels so high that it caused plant levels and growth to explode to great amounts. The massive amounts of plants provided enough food for the enormous vegetarians to survive and live. Another question that was brought up is how heavy must their bones be to support such weight? Most would think the bones weighted more but actually the muscle is what gave the giants their weight. The bones were hallow just like modern birds today.

Megafauna comparison chart
[Harry-the-Fox]

So where are the dinosaurs’s today? What killed off the dinosaurs? Well, one of the many hypotheses is that about sixty five million years ago, an asteroid with the energy of about one hundred million tons of TNT struck the earth and raised the earth’s temperature to thirteen hundred degrees Fahrenheit. Most of the lush vegetation was gone. All of the giant vegetarians died off because of no food, and then died the carnivores because off all other animals died. Most giant dinosaurs went extinct. Only animals that survived the blast were the warm blooded mammals similar to today’s rodents.

Today’s humans are an average of five foot eight inches. Fifty thousand years ago the average height was six feet. So what caused the shrinkage of humans? A changing environment. The changing environment killed off most of the humans prey they feed on. So they were forced to find a newer source of food, agriculture. They began to grow seeds and eating what grew out of the ground. This new life style couldn’t support their size so just like the pygmy mammoth, they shrunk. Now in days we have a better nutrition diet and so we are starting to grow in average height. And also what is promoting taller humans are women choosing mates that are tall. If taller men continue to reproduce than later generations will continue to be taller. With time the average height can jump from today’s five foot eight to six feet again.

“As human beings and all life on earth moves to the future, all the factors affecting body size from mating, to predation and to environment will continue to be in play and are likely to produce amazing and unexpected results as size continues to evolve.” [unknown author]

Recommended reading: Size Matters: The Genes Behind Adaptation by Virginia Morell

About the Author

I'm Jose Pierre and I like learning about all aspects of culture, both ancient and modern. I enjoy learning how they communicated, expressed themselves, and their technology.

About the Author

I'm Jose Pierre and I like learning about all aspects of culture, both ancient and modern. I enjoy learning how they communicated, expressed themselves, and their technology.

Evolution is the process by which populations of organisms acquire and pass on traits from generation to generation, affecting the overall makeup of the population and even leading to the emergence of new species. The terms organic evolution or biological evolution are often used to distinguish this meaning from other usages.

Evolution of a species is determined by many factors. Natural selection being the most determining factor. Natural selection favors traits more use full for the organisms given environment, organisms without these certain traits die out, so organisms with the favorable traits will survive and reproduce thus spreading the favorable trait.

Isolation can cause groups of the same species to speciate, a new species is developed within a species due to natural selection. Each isolated group develops traits that will benefit themselves. This causes derived traits to form in the lineage. Derived traits are slight changes in the ancestral traits.

There are two evolutionary traits that describe lineage. The first is called gradualism. In a complete evolutionary lineage, a finely graded transitional difference occurs between each ancestor and its descendants. This means that species gradually evolve and show differences in derived traits but keep similar ancestral traits. Traits will be specialized to suit the species given environment. The second explanation punctuated equilibrium. Punctuated equilibrium is the concept that evolutionary change proceeds through long periods of stasis punctuated by rapid periods of change. This concept favors a non-gradual evolution. It favors the idea of quick spurts through time. One thing is certain that species do evolve as time passes by. So much time is needed to see physical change in species.

Natural selection causes variations in humans. There are three variations: morphological, physiological, and behavioral. Morphological variation includes shapes and proportions, colder climates tend to have smaller chunkier people and hot places have thinner and leaner people. Physiological variation includes dietary size. Some places people are used to certain food nutrition and limits the maximum size of their body. The amount of clothes a person wears to suit its environment is behavioral variation. People in places with colder temperatures wear more clothes than people in warmer climates.

Natural selection is essential for the survival of life on Earth. It is the tendency of the most fit organisms to survive in their given environment. Surviving individuals result in a favorable variation of traits in the species. Like the cheetah, over time its developed the ability to run fast, because of environmental pressure. Another form of natural selection is human-induced selection, which is called artificial selection.

Artificial selection is forced breeding and human driven domestication of plants and animals. It is used to make growth of the plants and animals increase so it can meet the demands of the humans. 

Artificial selection gave birth to many of the diseases we face today. Living in close proximity with live stock is a main cause. We have bred livestock for so long that many wild species have disappeared - now these animals only function as "food". Plus, we have altered agriculture. Grains now produce more, but their root systems are shallow. Shallow root systems increase the probability of erosion. We have completed altered our ecosystem with artificial selection. So we have unlimited supplies of food thanks to science, but this same science has caused elevated levels of greenhouse gases. 

The Earth goes through natural phases of increased greenhouse gases - yes, it is NATURAL. However, the rate of increase today is not natural. Our artificial selection processes have toyed with natural selection. We have damaged our home. Evolution is supposed to be natural, caused by the environment. Can we fix this? Yes! Are we trying to fix the problem? Some of us are. Join the cause, let's revive natural selection so all these wonderful species in our world can adapt to the changes and continue to exist.

Read more about how artificial selection is damaging the world!

About the Author

I'm Jose Pierre and I like learning about all aspects of culture, both ancient and modern. I enjoy learning how they communicated, expressed themselves, and their technology.