March 10, 2010

WASHINGTON: By delving deeper into the long calls of male Orangutans in Borneo, scientists have got new insight into how these solitary apes communicate through dense jungle.

The researchers conducted an acoustic analysis of the calls, and revealed that the calls not only serve to attract females, but also contain information on the identity and the context of the caller.

Led by Prof. Dr. Carel van Schaik from the University of Zurich, the researchers followed three sexually active male Organutans ‘Niko’, ‘Kentung’ and ‘Fugit’ from a nature reserve in Tuanan, Borneo.

The research area covered 750 hectares of heavily logged peat swamp forest where the average Orangutan density is 4.25 per square kilometre.

“Orangutans have a rich repertoire of calls, however only sexually mature, flanged males emit long-distance calls with a series of long booming pulses and grumbles which can be heard through over 1 km of dense jungle. Individual recognition is important in long distance communication when individuals are separated beyond visual contact, we examined whether individual identity and context were also encoded into a long call,” said co-author Dr Brigitte Spillmann.

They documented the behaviour of the three Orangutans each time they emitted a long call and their behaviour patterns were divided into two categories.

Frequently the males would emit spontaneous calls where there is no obvious prompt identified by the observers.

They would also call out in an aroused state in response to social prompts, such as another male’s long call, when a tree falls nearby and when the caller pushes over a tree themselves.

This tree pushing is known as ’snag crashing’, when the caller pushes over a dead tree in a noisy display of dominant behaviour, comparable to chest beating in Gorillas.

If a flanged male hears a tree falling nearby, it could suggest a rival male is ’snag crashing’ and can lead to a long call being given in response.

Long calls emitted in an aroused state are slightly faster, have pulses of shorter duration and contain more pulses and bubbles than spontaneously emitted calls.

After observing these categories of behaviour, the team also analysed how female Orangutans respond to the long calls.

They discovered that Bornean females recognise not only who is calling, as in previous research, but also clear differences in the acoustic characteristics of long calls emitted in different contexts.

The team monitored the responses between a calling male and a female who had heard the call but was not associated with the caller.

Females with dependent offspring moved away from spontaneous calls whereas a small sample of sexually active females seem to approach the caller.

When an aroused long call was heard females appeared to ignore the caller.

“This may be because in Borneo females with offspring and rival males are not the target of the spontaneous long calls, but are eavesdroppers. However the cost to the caller goes up if there is a more dominant male eavesdropper who may respond,” concluded Spillman.

“Long calls given in response to a disturbance are likely intended to repel rivals or potential predators, which accounts for the females’ lack of reaction compared to spontaneous long calls. Females are able to tell the difference between the types of long call and they react accordingly,” he added.

The study was published in Ethology.

Source: http://www.dnaindia.com/scitech/report_how-orangutans-communicate-through-dense-jungle_1357586

March 9, 2010
Source: CBC News

The calls of male orangutans contain information about the apes’ identity and the context of the call, researchers say.

An international team of researchers, led by Carel van Schaik of the University of Zurich, tracked the behaviour and calls of three male orangutans on a nature reserve in Borneo’s Indonesian region.

While all orangutans have a wide variety of calls, only sexually mature male orangutans with enlarged cheek pads, or flanges, can make long-distance calls through the jungle.

Brigitte Spillmann of the University of Zurich described the calls as “a series of long, booming pulses and grumbles, which can be heard through over a kilometre of dense jungle.”

The researchers wanted to know whether these “long calls” contain information about the identity of the ape and the reason for the call.

“Individual recognition is important in long-distance communication when individuals are separated beyond visual contact. We examined whether individual identity and context were also encoded into a long call,” Spillmann said in a release.

The scientists observed the orangutans and recorded their behaviours each time they emitted a call. Their results were published this week in the journal Ethology.

Calls may be response

Some of the apes’ calls were spontaneous and not provoked by any obvious prompt. Other calls were in response to behaviours of other apes, such as another male’s long call or a tree falling nearby.

Orangutans will sometimes push over trees as part of a noisy, dominant display called snag crashing, similar to chest pounding in gorillas.

The researchers found that the orangutans’ pulsing calls in response to snag crashing or another male’s call were faster and consisted of more pulses of shorter duration than calls that were spontaneous.

The scientists also observed the behaviour of some female orangutans who heard the male apes’ calls.

Females with young offspring moved away from males making spontaneous calls, while sexually active females seemed to move toward them.

“This may be because in Borneo, females with offspring and rival males are not the target of the spontaneous long calls, but are eavesdroppers. However, the cost to the caller goes up if there is a more dominant male eavesdropper who may respond,” said Spillmann.

The females who heard the calls that were in response to another male’s behaviour ignored them.

“Long calls given in response to a disturbance are likely intended to repel rivals or potential predators, which accounts for the females’ lack of reaction, compared with spontaneous long calls. Females are able to tell the difference between the types of long call and they react accordingly,” said Spillmann.

Read more: http://www.cbc.ca/technology/story/2010/03/09/tech-biology-orangutan-call.html

Review

“This book is an impressive collaborative effort with over 70 authors contributing to a series of broad comparative chapters that document what we do and do not know about the similarities and differences among separate orangutan populations in many parts of Northern Sumatra and Borneo. This is behavioral ecology and evolutionary biology at its finest.”–The Quarterly Review of Biology

Description

This book describes one of our closest relatives, the orangutan, and the only extant great ape in Asia. It is increasingly clear that orangutan populations show extensive variation in behavioural ecology, morphology, life history, and genes. Indeed, on the strength of the latest genetic and morphological evidence, it has been proposed that orangutans actually constitute two species which diverged more than a million years ago – one on the island of Sumatra the other on Borneo, with the latter comprising three subspecies.

This book has two main aims. The first is to carefully compare data from every orangutan research site, examining the differences and similarities between orangutan species, subspecies, and populations. The second is to develop a theoretical framework in which these differences and similarities can be explained. To achieve these goals the editors have assembled the world’s leading orangutan experts to rigorously synthesize and compare the data, quantify the similarities or differences, and seek to explain them.

Orangutans is the first synthesis of orangutan biology to adopt this novel, comparative approach. It analyses and compares the latest data, developing a theoretical framework to explain morphological, life history, and behavioural variation. Intriguingly, not all behavioural differences can be attributed to ecological variation between and within the two islands; relative rates of social learning also appear to have been influential. The book also emphasizes the crucial impact of human settlement on orangutans and looks ahead to the future prospects for the survival of critically endangered natural populations.

Source: http://www.rgj.com/article/20100220/NEIGHBORHOODS/2200318/1247

February 20, 2010

Megan and Katie, two dogs who share a home, enjoy their chew toys together, side by side. But if Katie gets up to go out, she leaves her toy behind. No sooner is she out of sight than Meagan springs up, grabs Katie’s toy, stashes it in a hiding place and returns to her spot. When Katie returns, she looks around for her toy while Megan maintains an air of innocent detachment all the while watching the search.

Spike, a tabby cat, hears another cat coming up the stairs and hides behind a door. When Jill, a calico housemate, walks by, Spike springs out, causing Jill to cry out in alarm and bound off. Spike seems quite pleased with the result.

These sorts of antics certainly have the power to amuse and sometimes annoy us when we witness them in our pets. I suppose that someone could explain them away as being related to the control of territory or resources, but on the other hand, these acts are not all that different from the practical jokes played by children. Could it be that animals have a sense of humor?

Recent studies suggest that some animals, indeed, do seem to enjoy a good laugh. The idea that animals have a sense of humor may not be as far fetched as was once assumed. Most human babies learn to laugh before they can talk, which experts say indicates that our sense of fun, joy and laughter originates in the more basic areas of the brain. Toddlers laugh as often as 400 times a day. Considering that some animals have the same intelligence level as 2-year-old children, it seems possible that our pets could be laughing, too.

“Neural circuits for laughter exist in very ancient regions of the brain, and ancestral forms of play and laughter existed in other animals eons before we humans came along with our verbal repartee,” says Jaak Panksepp, a neuroscientist at Bowling Green State University.

Studies of rats, monkeys and dogs show that some of the sounds they make are likely related to laughter. Chimps at play pant in a way similar to human laughter, and some experts think that dogs show a similar huffing response during play. Rats make high-pitched squeaks or chirps while playing with each other or when being tickled by a human.

Studies with orangutans show that they exhibit what is known as emotional contagion in humans. When one orangutan displays a facial expression, its playmate often quickly responds with the same expression. Emotional contagion is a form of empathy that permits us to experience the emotions of those around us.

While not the same as laughter, play is an instinctive behavior for all mammals, including cats, dogs and people. While young animals and children tend to play with greater enthusiasm than adults, playful activity persists throughout a lifetime for many.

Play in children almost certainly serves as practice for important adult behaviors, but it also helps to develop social connections. Researchers are now admitting that play could have another purpose for both people and animals — plain old fun.

Why would play and the expression of enjoyment be such an important activity and basic brain function? It could be because it is beneficial for us. Laughter is known to lower blood pressure and reduce stress in humans, and it might have a similar function for animals.

Even if you remain skeptical about pets having a sense of humor, one thing is for sure: They bring humor and a sense of play back into our lives. And given life’s many stresses, that is a wonderful blessing.

Bonney Brown is the Nevada Humane Society’s executive director.

By NICHOLAS WADE
Source: The New York Times

January 12, 2010 — Walking through the Tai forest of Ivory Coast, Klaus Zuberbühler could hear the calls of the Diana monkeys, but the babble held no meaning for him.

That was in 1990. Today, after nearly 20 years of studying animal communication, he can translate the forest’s sounds. This call means a Diana monkey has seen a leopard. That one means it has sighted another predator, the crowned eagle. “In our experience time and again, it’s a humbling experience to realize there is so much more information being passed in ways which hadn’t been noticed before,” said Dr. Zuberbühler, a psychologist at the University of St. Andrews in Scotland.

Do apes and monkeys have a secret language that has not yet been decrypted? And if so, will it resolve the mystery of how the human faculty for language evolved? Biologists have approached the issue in two ways, by trying to teach human language to chimpanzees and other species, and by listening to animals in the wild.

The first approach has been propelled by people’s intense desire — perhaps reinforced by childhood exposure to the loquacious animals in cartoons — to communicate with other species. Scientists have invested enormous effort in teaching chimpanzees language, whether in the form of speech or signs. A New York Times reporter who understands sign language, Boyce Rensberger, was able in 1974 to conduct what may be the first newspaper interview with another species when he conversed with Lucy, a signing chimp. She invited him up her tree, a proposal he declined, said Mr. Rensberger, who is now at M.I.T.

But with a few exceptions, teaching animals human language has proved to be a dead end. They should speak, perhaps, but they do not. They can communicate very expressively — think how definitely dogs can make their desires known — but they do not link symbolic sounds together in sentences or have anything close to language.

Better insights have come from listening to the sounds made by animals in the wild. Vervet monkeys were found in 1980 to have specific alarm calls for their most serious predators. If the calls were recorded and played back to them, the monkeys would respond appropriately. They jumped into bushes on hearing the leopard call, scanned the ground at the snake call, and looked up when played the eagle call.

It is tempting to think of the vervet calls as words for “leopard,” “snake” or “eagle,” but that is not really so. The vervets do not combine the calls with other sounds to make new meanings. They do not modulate them, so far as is known, to convey that a leopard is 10, or 100, feet away. Their alarm calls seem less like words and more like a person saying “Ouch!” — a vocal representation of an inner mental state rather than an attempt to convey exact information.

But the calls do have specific meaning, which is a start. And the biologists who analyzed the vervet calls, Robert Seyfarth and Dorothy Cheney of the University of Pennsylvania, detected another significant element in primates’ communication when they moved on to study baboons. Baboons are very sensitive to who stands where in their society’s hierarchy. If played a recording of a superior baboon threatening an inferior, and the latter screaming in terror, baboons will pay no attention — this is business as usual in baboon affairs. But when researchers concoct a recording in which an inferior’s threat grunt precedes a superior’s scream, baboons will look in amazement toward the loudspeaker broadcasting this apparent revolution in their social order.

Baboons evidently recognize the order in which two sounds are heard, and attach different meanings to each sequence. They and other species thus seem much closer to people in their understanding of sound sequences than in their production of them. “The ability to think in sentences does not lead them to speak in sentences,” Drs. Seyfarth and Cheney wrote in their book “Baboon Metaphysics.”

Some species may be able to produce sounds in ways that are a step or two closer to human language. Dr. Zuberbühler reported last month that Campbell’s monkeys, which live in the forests of the Ivory Coast, can vary individual calls by adding suffixes, just as a speaker of English changes a verb’s present tense to past by adding an “-ed.”

The Campbell’s monkeys give a “krak” alarm call when they see a leopard. But adding an “-oo” changes it to a generic warning of predators. One context for the krak-oo sound is when they hear the leopard alarm calls of another species, the Diana monkey. The Campbell’s monkeys would evidently make good reporters since they distinguish between leopards they have observed directly (krak) and those they have heard others observe (krak-oo).

Even more remarkably, the Campbell’s monkeys can combine two calls to generate a third with a different meaning. The males have a “Boom boom” call, which means “I’m here, come to me.” When booms are followed by a series of krak-oos, the meaning is quite different, Dr. Zuberbühler says. The sequence means “Timber! Falling tree!”

Dr. Zuberbühler has observed a similar achievement among putty-nosed monkeys that combine their “pyow” call (warning of a leopard) with their “hack” call (warning of a crowned eagle) into a sequence that means “Let’s get out of here in a real hurry.”

Apes have larger brains than monkeys and might be expected to produce more calls. But if there is an elaborate code of chimpanzee communication, their human cousins have not yet cracked it. Chimps make a food call that seems to have a lot of variation, perhaps depending on the perceived quality of the food. How many different meanings can the call assume? “You would need the animals themselves to decide how many meaningful calls they can discriminate,” Dr. Zuberbühler said. Such a project, he estimates, could take a lifetime of research.

Monkeys and apes possess many of the faculties that underlie language. They hear and interpret sequences of sounds much like people do. They have good control over their vocal tract and could produce much the same range of sounds as humans. But they cannot bring it all together.

This is particularly surprising because language is so useful to a social species. Once the infrastructure of language is in place, as is almost the case with monkeys and apes, the faculty might be expected to develop very quickly by evolutionary standards. Yet monkeys have been around for 30 million years without saying a single sentence. Chimps, too, have nothing resembling language, though they shared a common ancestor with humans just five million years ago. What is it that has kept all other primates locked in the prison of their own thoughts?

Drs. Seyfarth and Cheney believe that one reason may be that they lack a “theory of mind”; the recognition that others have thoughts. Since a baboon does not know or worry about what another baboon knows, it has no urge to share its knowledge. Dr. Zuberbühler stresses an intention to communicate as the missing factor. Children from the youngest ages have a great desire to share information with others, even though they gain no immediate benefit in doing so. Not so with other primates.

“In principle, a chimp could produce all the sounds a human produces, but they don’t do so because there has been no evolutionary pressure in this direction,” Dr. Zuberbühler said. “There is nothing to talk about for a chimp because he has no interest in talking about it.” At some point in human evolution, on the other hand, people developed the desire to share thoughts, Dr. Zuberbühler notes. Luckily for them, all the underlying systems of perceiving and producing sounds were already in place as part of the primate heritage, and natural selection had only to find a way of connecting these systems with thought.

Yet it is this step that seems the most mysterious of all. Marc D. Hauser, an expert on animal communication at Harvard, sees the uninhibited interaction between different neural systems as critical to the development of language. “For whatever reason, maybe accident, our brains are promiscuous in a way that animal brains are not, and once this emerges it’s explosive,” he said.

In animal brains, by contrast, each neural system seems to be locked in place and cannot interact freely with others. “Chimps have tons to say but can’t say it,” Dr. Hauser said. Chimpanzees can read each other’s goals and intentions, and do lots of political strategizing, for which language would be very useful. But the neural systems that compute these complex social interactions have not been married to language.

Dr. Hauser is trying to find out whether animals can appreciate some of the critical aspects of language, even if they cannot produce it. He and Ansgar Endress reported last year that cotton-top tamarins can distinguish a word added in front of another word from the same word added at the end. This may seem like the syntactical ability to recognize a suffix or prefix, but Dr. Hauser thinks it is just the ability to recognize when one thing comes before another and has little to do with real syntax.

“I’m becoming pessimistic,” he said of the efforts to explore whether animals have a form of language. “I conclude that the methods we have are just impoverished and won’t get us to where we want to be as far as demonstrating anything like semantics or syntax.”

Yet, as is evident from Dr. Zuberbühler’s research, there are many seemingly meaningless sounds in the forest that convey information in ways perhaps akin to language.

Source: http://www.eurekalert.org/pub_releases/2009-12/asu-fmp122809.php

TEMPE, Ariz. – The timing of molar emergence and its relation to growth and reproduction in apes is being reported by two scientists at Arizona State University’s Institute of Human Origins in the Dec. 28 online early edition of the Proceedings of the National Academy of Sciences (PNAS).

From the smallest South American monkeys to the largest African apes, the timing of molar development and eruption is closely attuned to many fundamental aspects of a primate’s biology, according to Gary Schwartz, a researcher at the Institute of Human Origins and an associate professor in the School of Human Evolution and Social Change in ASU’s College of Liberal Arts and Sciences.

“Knowing the age when the first molar appears in the mouths of most primates allows researchers to predict a host of life history attributes, such as gestation length, age at sexual maturity, birth spacing, and overall lifespan. Humans are unique among primates because our life histories are so slow and thus our molars emerge relatively late. Given that apes are our closest living relatives, understanding the broader context of when the characteristic slower development of humans evolved is of great interest,” Schwartz explains.

“We’ve known quite a bit about the timing of molar development in chimpanzees, which is important because they are our closest living relative. However, we’ve known virtually nothing about when this important event occurs in other wild-living ape species – until now,” says lead author Jay Kelley, a research affiliate at ASU’s Institute of Human Origins and an associate professor in the Department of Oral Biology at the University of Illinois, Chicago.

Because of the difficulties in obtaining tooth emergence ages from animals in the wild, Kelley opted for other means; he searched for specimens in museums. At the Zoologische Staatssammlung in Munich he found skulls of a wild-shot orangutan (Pongo pygmaeus pygmaeus) and gorilla (Gorilla gorilla gorilla) that preserved emerging first molars.

“Like annual growth rings inside trees, the cells that produce teeth (both the enamel and underlying dentine) leave behind a trace of their presence, not as annual markers, but as growth lines that appear every day,” says Kelley. By slicing the teeth in half, he and Schwartz were able to examine these incremental growth lines in ape individuals that died as their first molars were just erupting into their mouths.

“Because teeth preserve this phenomenal internal chronometer, we were able to count up how many days it took the first molars to form. In apes and monkeys, first molars start forming very close to the time of birth. As the first molars were still erupting in our specimens, development was incomplete and the final growth line was laid down on the day those animals died. Therefore, by counting backwards from the final growth line to the day of birth, we determined their age at death and thus the age at which that molar was erupting” says Schwartz.

Using this novel approach, the two scientists were able to mark the age of the gorilla’s first molar emergence at 3.8 years, nearly identical to that of a wild chimpanzee’s. The orangutan’s age at first molar emergence was surprisingly much later, at 4.6 years, which falls closer to the age of approximately 6 years in modern humans.

“We were excited to discover this much older age for the orangutan, since orangutans have much slower life histories than the other two great apes,” says Kelly.

However, he and Schwartz caution that though the later emergence age in these large Asian apes is closer to that for modern humans, these latest findings should not be taken to indicate some special evolutionary relationship between the two. “Rather, it is in keeping with what you would expect given the relatively slow pace of growth and long period of infant dependency that evolved separately in the lineage leading to orangutans and that leading to modern humans,” says Schwartz.

The work by Kelley and Schwartz also has implications for understanding the evolution of human life history. “We can use the same techniques to calculate ages at first molar emergence from the fossils of early hominids that just happened to die while their first molars were erupting,” says Kelley. “The close correspondence between age at first molar emergence and the timing of life history events that we found in great apes and modern humans means that we can have confidence that first molar emergence ages in the early hominids will provide equally accurate knowledge about their life histories.”

Their findings are detailed in the article “Dental development and life history in living African and Asian apes.”

###

ARIZONA STATE UNIVERSITY (www.asu.edu)
College of Liberal Arts and Sciences (http://clas.asu.edu)
Institute of Human Origins (http://iho.asu.edu)
School of Human Evolution and Social Change (http://shesc.asu.edu)
Tempe, Arizona USA

Forthcoming book examines the role of humans in the eradication of species, and its findings are not likely to be pleasant

Robin McKie
Source: The Observer, Sunday 8 November 2009

At first sight it seems an unlikely topic for a landmark publishing deal: a fee of about half a million dollars for a book about dead animals – or, to be more precise, extinct animals.

Nevertheless the subject of eradicated species has become publishing hot property after a bidding battle in the US saw Henry Holt, a publisher, beat its rivals to buy The Sixth Extinction by Elizabeth Kolbert last week. According to the New York Times, a “mid-six-figure advance” has now been agreed between writer and publisher.

“The idea of mass extinctions as the next step after talking about the perils of global warming is the most crucial subject,” said Gillian Blake of Holt, after completing the deal with Kolbert, a writer for the New Yorker on environmental issues. Her last book, Field Notes from a Catastrophe, outlined evidence collated from sites across the planet showing how global warming is changing the world. The book was well reviewed on both sides of the Atlantic, with the Observer praising it as “a superbly crafted, diligently compressed vision of a world spiralling towards destruction”.

Now, Kolbert is to focus on humanity’s impact on the animal world, and in particular will look at the species that are today being rendered extinct by men and women. Scientists say the number of species being lost is approaching levels reached during five pivotal extinction events that have swept the planet over the past 600 million years. Among these catastrophes was the event that wiped out the dinosaurs 65 million years ago. Kolbert’s task will to be show whether or not humanity – with its spiralling population, widespread habitat destruction, over-fishing and global warming – is rivalling these.

The theme is intriguing but not new. Nor is the title. In 1996 the distinguished palaeontologist Richard Leakey, with journalist Roger Lewin, produced his version of The Sixth Extinction, in which he argued that the five previous mass extinction events were now being matched by a sixth. “Homo sapiens is poised to become the greatest catastrophic agent since a giant asteroid collided with the Earth 65 million years ago, wiping out half the world’s species in a geological instant,” he says.

Other distinguished scientists, including EO Wilson and Norman Myers, have also produced works on this theme. None received advances like the one agreed between Holt and Kolbert, however. So what has changed? Why have extinctions become the subject of such attention and finance?

Answers have much to do with timing. Over the past decade, there has been a revolution in concerns about the environment – on both sides of the Atlantic. A succession of reports from United Nations wildlife experts and climate scientists have shown that our planet is in peril and that thousands of species are now hovering on the brink of extinction. For a decade, the public has been deluged with stories about the vulnerability of the tiger, coral reefs, amphibians and a host of other creatures. Hence the interest in Kolbert’s new book.

In publishing terms, the move is also a significant one because it represents a shift from big-money outlays on works of fiction which have dominated the market in recent years. Huge sums, for example, have been paid to novelists such as Audrey Niffenegger for works – such as her latest, Her Fearful Symmetry – that have had disappointing sales. A dose of eco-horror might prove rewarding, it is thought.

Certainly, extinctions make a riveting and disconcerting subject. As Professor Norman MacLeod, keeper of palaeontology at the Natural History Museum in London, told the Observer: “We now know that 99.9% of all lifeforms that have ever existed on Earth have gone extinct. That means, to a first order approximation, that all life is extinct.”

Obviously this latter, rather disturbing, scenario has not quite arrived. Nevertheless it does indicate that the constant eradication of lifeforms has been the norm throughout the history of life on Earth. It is the fate of all species to become extinct, a notion that should concentrate the minds of Kolbert’s readers. The question is: what forces are responsible for the loss of vast numbers of species in such a short period?

Answers depend on individual cases, it transpires. For example, a huge asteroid crashing on Earth 65 million years ago is generally thought to have done for the dinosaurs. The vast plume thrown up by the impact coated the planet in dust and triggered a devastating climate change. As a result, 47% of marine genera (groups of related species) and 18% of land vertebrate families, including the dinosaurs, were wiped out.

And as evidence geologists point to the Chicxulub crater near the Yucatán peninsula, beneath the Gulf of Mexico, as the impact point of the asteroid.

Similarly the Triassic extinction, which occurred between 199 million and 214 million years ago, was most likely caused by massive floods of lava erupting from the Atlantic Ocean. These created a wave of global warming. In this case, around 22% of marine families and 52% of marine genera were eradicated.

Then there was the Permian-Triassic extinction, about 250 million years ago, which has been linked to both asteroid impacts and volcanism. This was Earth’s worst mass extinction, killing 95% of all species, including an estimated 70% of land species such as plants, insects and vertebrate animals. Before that, the Late Devonian extinction, about 360 million years ago, killed 57% of marine genera. Its cause remains unknown. And finally, there was the Ordovician-Silurian extinction, about 440 million years ago, which has been linked with changes in sea levels and which led to the eradication of 60% of marine genera.

Life on Earth has, on some occasions, become remarkably unpleasant in a short space of time, to say the least – though this has not always been the prevailing view among scientists. In fact, Darwin thought extinction was a slow, painful business. “The complete extinction of the species of a group is generally a slower process than their production,” he once remarked, a view that held sway for more than a century. Indeed it was only in the latter half of the 20th century that scientists uncovered evidence – the Chicxulub crater – that an asteroid crash must have been involved in the demise of dinosaurs. Extinctions could be sudden, they realised.

However, MacLeod urged caution in interpreting such discoveries. “Most palaeontologists dislike the idea that any single cause was responsible for one of the main extinctions,” he said.

“Life is very robust and it takes a sequence of events to produce large-scale extinctions.”

Thus the dinosaurs were wiped out at a time of considerable volcanic activity on Earth. Plumes of material were already sweeping the planet, plunging it into a period of global cooling. The crashing asteroid then administered a planetary coup de grace.

On top of volcanoes and errant astronomical objects, other factors involved in these mass extinctions include extreme ice ages which coated the planet in ice from pole to equator, and eruptions of deep-sea methane deposits that set off massive global warming. The resulting death toll is measured in millions of species.

What remains unclear is the degree to which humans are now repeating this bloodletting, to the extent that we are about to set off a sixth extinction wave. If so, we will be the first single, biological cause of this kind of catastrophe. “If you add up the numbers of species that have been wiped out over the past few hundred years, then you find the figures fall well short of a mass extinction,” said MacLeod. “It is only when you look at the numbers of creatures that are poised at the brink of eradication does the picture become alarming.”

Tigers, coral reefs and all the marine life they support, amphibians such as the golden frog of Panama, orang-utans, sharks, mountain gorillas, the marine iguanas of the Galápagos, albatrosses, chimpanzees and thousands of other creatures now face obliteration: hunted, rendered homeless, and poisoned by humans.

More to the point, this predation has been going on, not for hundreds of years, but for tens of thousands of years.

Whenever Homo sapiens has moved into new territory, this has been followed quickly by the disappearance of most large land mammals, palaeontologists have found. For example, the Clovis people, ancient hunters armed with fearsome stone-tipped spears, arrived in North America 12,000 years ago.

A total of 75 species, including woolly mammoths, mastodons, four-horned antelopes and lumbering sloths the size of giraffes were killed off almost immediately. A thousand years later, the slaughter continued in South America when humans arrived there.

The glyptodon (a giant armadillo-like animal), several species of rodent and various llama-like animals were wiped out. And a similar bloodbath occurred in Australia with the arrival of the first members of Homo sapiens.

In short, humanity has a great deal of blood on its hands, spears and guns. Whether we maintain this kind of eradication of our fellow Earthlings remains to be seen. Most experts predict grim times, an outcome that will provide Kolbert with the core of her ambitious look at the fate of our planet – and at the fate of the animals who are trying, unsuccessfully, to share it with human beings.